This article has been tagged since July 2006.
Space-filling model of a polyethylene chain
The repeating unit of polyethylene, showing its stereochemistry
A simpler way of representing the repeating unit. Note, however, that the C−H bond angles are not 90° as this diagram would indicate, but are approximately 110°, since each carbon atom is tetrahedral (sp3).Polyethylene, (IUPAC name polyethene), is a thermoplastic commodity heavily used in consumer products (over 60 million tons are produced worldwide every year). It is a polymer consisting of long chains of the monomer ethylene (IUPAC name ethene).
In the polymer industry the name is sometimes shortened to PE, in a manner similar to that by which other polymers like polypropylene and polystyrene are shortened to PP and PS, respectively. In the United Kingdom the polymer is called polythene.
The ethene molecule (known almost universally by its common name ethylene), C2H4 is CH2=CH2, Two CH2 groups connected by a double bond, thus:
Polyethylene is created through polymerization of ethene. It can be produced through radical polymerization, anionic addition polymerization, ion coordination polymerization or cationic addition polymerization. This is because ethene does not have any substituent groups which influence the stability of the propagation head of the polymer. Each of these methods results in a different type of polyethylene.
Classification of polyethylenes
Polyethylene is classified into several different categories based mostly on its density and branching. The mechanical properties of PE depend significantly on variables such as the extent and type of branching, the crystal structure, and the molecular weight.
UHMWPE (ultra high molecular weight PE)
HMWPE (high molecular weight polyethylene)
HDPE (high density PE)
HDXLPE (high density cross-linked PE)
PEX (cross-linked PE)
MDPE (medium density PE)
LDPE (low density PE)
LLDPE (linear low density PE)
VLDPE (very low density PE)
UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.1 and 5.67 million. The high molecular weight results in less efficient packing of the chains into the crystal structure as evidenced by densities less than high density polyethylene (e.g. 0.935 - 0.930). The high molecular weight results in a very tough material. UHMWPE can be made through any catalyst technology, although Ziegler catalysts are most common. Because of its outstanding toughness, cut, wear and excellent chemical resistance, UHWMPE is used in a wide diversity of applications. These include can and bottle handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks, butchers' chopping boards. It has even replaced Kevlar in new bulletproof vests.
HDPE is defined by a density of greater or equal to 0.941 g/cc. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (e.g. Chromium catalysts or Ziegler-Natta catalysts) and reaction conditions. HDPE used in products and packaging such as milk jugs, detergent bottles, margarine tubs, and garbage containers.
PEX is a medium- to high-density polyethylene containing cross-link bonds introduced into the polymer structure, changing the thermoplast into an elastomer. The high-temperature properties of the polymer are improved, its flow is reduced and its chemical resistance is enhanced. PEX is used in some potable water plumbing systems, as tubes made of the material can be expanded to fit over a metal nipple, and it will slowly return to its original shape, forming a permanent, water-tight connection.
MDPE is defined by a density range of 0.926 - 0.940 g/cc. MDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts.MDPE has good shock and drop resistance properties. It also is less notch sensitive than HDPE, stress cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags, screw closures.
LLDPE is defined by a density range of 0.915 - 0.925 g/cc. is a substantially linear polymer, with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (e.g. 1-butene, 1-hexene, and 1-octene). LLDPE has higher tensile strength than LDPE. Exhibits higher impact and puncture resistance than LDPE. Lower thickness (gauge) films can be blown compared to LDPE, with better environmental stress cracking resistance compared to LDPE but is not as easy to process LLDPE is used in packaging, particularly film for bags and sheets. Lower thickness (gauge) may be used compared to LDPE. Cable covering, toys, lids, buckets and containers, pipe.While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility, and relative transparency.
LDPE is defined by a density range of 0.910 - 0.940 g/cc. LDPE has a high degree of short and long chain branching, which means that the chains do not pack into the crystal structure as well. It has therefore less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. LDPE is created by free radical polymerization. The high degree of branches with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap.
VLDPE is defined by a density range of 0.880 - 0.915 g/cc. is a substantially linear polymer, with high levels of short chain branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (e.g. 1-butene, 1-hexene, and 1-octene). VLDPE is most commonly produced using metallocene catalysts due to the greater co-monomer incorporation exhibited by these catalysts. VLDPE’s are used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap, as well as impact modifiers when blended with other polymers.
HDPE is also widely used in the fireworks community. In tubes of varying length (depending on the size of the ordnance), HDPE is used as a replacement for the supplied cardboard mortar tubes for two primary reasons. One, it is much safer than the supplied cardboard tubes because if a shell were to malfunction and explode inside (flower pot) an HDPE tube, the tube will not shatter. The second reason is that they are reusable allowing designers to create multiple shot mortar racks. Pyrotechnicians discourage the use of PVC tubing in mortar tubes because it will shatter, sending shards of plastic at possible spectators, and will not show up in x-rays.
Recently, much research activity has focused on the nature and distribution of Long Chain Branches in polyethylene. In HDPE, a relatively small number of these branches (perhaps 1 in 100 or 1000 branches per backbone carbon) can significantly affect the rheological properties of the polymer.
In addition to copolymerization with alpha-olefins, ethylene can also be copolymerized with a wide range of other monomers and ionic compositon that creates ionized free radicals. Common examples include vinyl acetate (resulting product is ethylene-vinyl acetate copolymer, or EVA, widely used in athletic shoe sole foams), and a variety of acrylates (applications include packaging and sporting goods).
Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it by accident in 1898 while heating diazomethane. When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy substance he had created, they recognized that it contained long -CH2- chains and termed it polymethylene.
The first industrially practical polyethylene synthesis was discovered (again by accident) in 1933 by Eric Fawcett and Reginald Gibson at the ICI works in Northwich, England. Upon applying extremely high pressure (several hundred atmospheres) to a mixture of ethylene and benzaldehyde, they again produced a white waxy material. Since the reaction had been initiated by trace oxygen contamination in their apparatus, the experiment was at first difficult to reproduce. It was not until 1935 that another ICI chemist, Michael Perrin, developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial LDPE production beginning in 1939.
Subsequent landmarks in polyethylene synthesis have centered around the development of several types of catalyst that promote ethylene polymerization at more mild temperatures and pressures. The first of these was a chromium trioxide based catalyst discovered in 1951 by Robert Banks and John Hogan at Phillips Petroleum. In 1953, the German chemist Karl Ziegler developed a catalytic system based on titanium halides and organoaluminum compounds that worked at even milder conditions than the Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are used in industrial practice.
By the end of the 1950s both the Phillips and Ziegler type catalysts were being used for HDPE production. Phillips' initially had difficulties producing a HDPE product of uniform quality, and filled warehouses with off-specification plastic. However, financial ruin was unexpectedly averted in 1957, when the hula hoop, a toy consisting of a circular polyethylene tube, became a fad among teenagers throughout the United States.
A third type of catalytic system, one based on metallocenes, was discovered in 1976 in Germany by Walter Kaminsky and Hansjörg Sinn. The Ziegler and metallocene catalyst families have since proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including VLDPE, and LLDPE. Such resins, in the form of fibers like Dyneema, have (as of 2005) begun to replace aramids in many high-strength applications.
Until recently, the metallocenes were the most active single-site catalysts for ethylene polymerisation known - new catalysts are typically compared to zirconocene dichloride. Much effort is currently being exerted on developing new single-site (so-called post-metallocene) catalysts, that may allow greater tuning of the polymer structure than is possible with metallocenes. Recently, work by Fujita at the Mitsui corporation (amongst others) has demonstrated that certain salicylaldimine complexes of Group 4 metals show substantially higher activity than the metallocenes.
Depending on the crystallinity and molecular weight, a melting point and glass transition may or may not be observable. The temperature at which these occur varies strongly with the type of polyethylene. For common commercial grades of medium-density and high-density polyethylene, the melting point is typically in the range 120-130 °C. The melt point for average commercial low-density polyethylene is typically 105-115 °C. Most LDPE, MDPE, and HDPE grades have excellent chemical resistance and do not dissolve at room temperature because of the crystallinity. Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in aromatic hydrocarbons (i.e. toluene, xylene) or chlorinated solvents (i.e. trichloroethane, trichlorobenzene).
HDPE ( High density polyethylene )
High density polyethylene
HDPE has SPI
resin ID code 2
High-density polyethylene (HDPE) is a polyethylene thermoplastic made from petroleum. It takes 1.75 kilograms of petroleum (in terms of energy and raw materials) to make one kilogram of HDPE.
HDPE has little branching, giving it stronger intermolecular forces and tensile strength than lower density polyethylene. It is also harder and more opaque and can withstand somewhat higher temperatures (120° Celsius for short periods, 110° Celsius continuously). The lack of branching is ensured by an appropriate choice of catalyst (e.g. Ziegler-Natta catalysts) and reaction conditions.
HDPE is resistant to many different solvents and has a wide variety of applications, including:
Laundry detergent bottles
Fuel tanks for cars
Containment of certain chemicals
Chemical-resistant piping systems
Geothermal heat transfer piping systems
Natural gas distribution pipe systems
Water distribution pipe systems
Coax cable inner insulators (dielectric insulating spacer)
Corrosion Protection for Steel Pipelines. See HDPE Liner
HDPE is also used for cell liners in subtitle D sanitary landfills, wherein large sheets of HDPE are either extrusion or wedge welded to form a homogeneous chemical-resistant barrier, preventing the pollution of soil and groundwater by the liquid constituents of solid waste.
One of the largest uses for HDPE is wood plastic composites, with recycled polymers leading the way.
LDPE ( Low density polyethylene )
Low density polyethylene
LDPE has SPI
resin ID code 4
Low-density polyethylene (LDPE) is a thermoplastic made from oil. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerisation . Its manufacture employs the same method today.
LDPE is defined by a density range of 0.910 - 0.940 g/cm³. It is unreactive at room temperatures, except by strong oxidizing agents, and some solvents cause its swelling. It can withstand temperatures of 80 °C continuously and 95 °C for a short time. Made in translucent or opaque variations, it is quite flexible, and tough to the degree of being almost unbreakable.
It has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced-dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. Also, since its molecules are less tightly packed and less crystalline because of the side branches, its density is lower.
Maximum Temperature: 176 °F (80 °C)
Minimum Temperature: −58 °F (−50 °C)
Melting Point: 248 °F (120 °C)
Tensile Strength: 1700 psi (11.7 MPa)
UV Resistance: Poor
Density: 0.92 g/cm³
Excellent resistance (no attack) to dilute and concentrated acids, alcohols, bases and esters.
Good resistance (minor attack) to aldehydes, ketones and vegetable oils.
Limited resistance (moderate attack suitable for short term use only) to aliphatic and aromatic hydrocarbons, mineral oils and oxidizing agents.
Poor resistance and not recommended for use with Halogenated hydrocarbons.
LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, and various molded laboratory equipment. Its most common use is in plastic bags. Other products made from it include:
Trays & general purpose containers
Food storage and laboratory containers
Corrosion-resistant work surfaces
Parts that need to be weldable and machinable
Parts that require flexibility, for which it serves very well
Very soft and pliable parts
Six-pack soda can rings
LLDPE ( Linear low density polyethylene )
Linear low density polyethylene (LLDPE) is a substantially linear polymer, with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins.
LLDPE has higher tensile strength and higher impact and puncture resistance than LDPE. It is very flexible and elongates under stress. It can be used to make thinner films, with better environmental stress cracking resistance. It has good resistance to chemicals and to ultraviolet radiation. It has good electrical properties. However it is not as easy to process as LDPE, has lower gloss, and narrower range for heat sealing.
It is used for plastic bags and sheets (where it allows using lower thickness than comparable LDPE), plastic wrap, pouches, toys, lids, pipes, buckets and containers, covering of cables, geomembranes, and mainly for flexible tubing.
LLDPE manufactured using metallocene catalysts is labeled mLLDPE.
Density 0.92 g/cm³
Surface hardness SD48
Tensile strength 20 MPa
Flexural modulus 0.35 GPa
Notched izod 1.06+ kJ/m
Linear expansion 20×10−5/°C
Elongation at break 500%
Strain at yield 20%
Max. operating temp. 50 °C
Water absorption 0.01%
Oxygen index 17%
Flammability UL94 HB
Volume resistivity log(16) Ω·cm
Dielectric strength 25 MV/m
Dissipation factor 1kHz 909090
Dielectric constant 1kHz 2.3
HDT @ 0.45 MPa 45 °C
HDT @ 1.80 MPa 37 °C
Material drying NA
Melting Temp. Range 120 to 160 °C
Mould Shrinkage 3%
Mould temp. range 20 to 60 °C
UHMWPE ( Ultra high molecular weight polyethylene )
Ultra high molecular weight polyethylene (UHMWPE), also known as high modulus polyethylene (HMPE) or high performance polyethylene (HPPE), is a thermoplastic. It has extremely long chains, with molecular weight numbering in the millions, usually between 3.1 and 5.67 million. The high molecular weight results from a very good packing of the chains into the crystal structure. This results in a very tough material, with the highest impact strength of any thermoplastic presently made. It is highly resistant to corrosive chemicals, with exception of oxidizing acids. It has extremely low moisture absorption, very low coefficient of friction, is self lubricating and is highly resistant to abrasion (10 times more resistant to abrasion than Carbon Steel). Its coefficient of friction is significantly lower than nylon and acetal, and is comparable to teflon, but UHMWPE has better abrasion resistance than teflon. It is odorless, tasteless, and nontoxic.
Structure and properties
Structure of UHMWPE, with n greater than 100,000UHMWPE is a type of polyolefin and, despite relatively weak Van der Waals bonds between its molecules, derives ample strength from the length of each individual molecule. It is made up of extremely long chains of polyethylene, which all align in the same direction. Each chain is bonded to the others with so many Van der Waals bonds that the whole can support great tensile loads.
When formed to fibers, the polymer chains can attain a parallel orientation greater than 95% and a level of crystallinity of up to 85%. In contrast, Kevlar derives its strength from strong bonding between relatively short molecules.
The weak bonding between olefin molecules allows local thermal excitations to disrupt the crystalline order of a given chain piece-by-piece, giving it much poorer heat resistance than other high-strength fibers. Its melting point is around 144 or 152 degrees Celsius, and according to DSM, it is not advisable to use UHMWPE fibers at temperatures exceeding 80 to 100°C for long periods of time. It becomes brittle at temperatures below -150°C.
The simple structure of the molecule also gives rise to surface and chemical properties that are rare in high-performance polymers. For example, the polar groups in most polymers easily bond to water. Because olefins have no such groups, UHMWPE does not absorb water readily, but it also does not get wet easily, which makes bonding it to other polymers difficult. For the same reasons, skin does not interact with it strongly, making the UHMWPE fiber surface feel slippery. Similarly, aromatic polymers are often susceptible to aromatic solvents due to aromatic stacking interactions, an effect aliphatic polymers like Dyneema are also immune to. Since Dyneema does not contain chemical groups (such as esters, amides or hydroxylic groups) that are susceptible to attack from aggressive agents, it is very resistant to water, moisture, most chemicals, UV radiation, and micro-organisms.
Under tensile load, UHMWPE will deform continually as long as the stress is present - an effect called creep.
UHMWPE is synthesized from monomers of ethylene, which are bonded together to form what is called ultra high molecular weight polyethylene (or UHMWPE). These are molecules of polyethylene which are several orders of magnitude longer than familiar, high density polyethylene due to a synthesis process based on metallocene catalysts. HDPE molecules generally have between 700 and 1,800 monomer units per molecule, while UHMWPE molecules tend to have 100,000 to 250,000 monomers each.
Dyneema or Spectra is a synthetic fiber based on ultra high molecular weight polyethylene which is 15 times stronger than steel and up to 40% stronger than Kevlar. It is usually used in bulletproof vests, bow strings, climbing equipment, fishing line and high performance sails in yachting. Dyneema was invented by DSM in 1979. It has been in commercial production since 1990 at a plant in Heerlen, the Netherlands. In the Far East, DSM has a cooperation agreement with Toyobo Co. for commercial production in Japan. In the United States, DSM has a production facility in Greenville, North Carolina which is the largest production facility in the United States for UHMWPE fiber. Honeywell has developed a chemically identical product on its own. The Honeywell product is sold under the brand name Spectra. Though the production details will undoubtedly be different, the resulting materials are comparable. This article refers to both materials by the name Dyneema. Dyneema is a registered trademark of Royal DSM N.V. (The Netherlands).
Other brand names include TIVAR by Poly Hi Solidur, Hostalen by Heochst GmbH, and Polystone-M by Rochling Engineered Plastics.
For body armor, the fibers are generally aligned and bonded into sheets, which are then layered at various angles to give the resulting composite material strength in all directions.
Both Spectra and Dyneema excel as fishing line as they have less stretch, are more abrasion resistant, and are thinner than traditional monofilament line.
In recent years certain items of climbing equipment have started making use of Dyneema. In particular "slings", sewn loops of material that can be wrapped around sections of rock, hitched (tied) to other pieces of equipment or even tied directly to a tensioned line using a special prussik knot, have benefited from this material. It has limited applications however as items made from this material do not stretch and therefore a fall on them involves considerable shock loading of the other pieces of equipment and the climber's body. They are however much lighter and finer than the alternatives (nylon) and therefore are very popular. Usually sold in lengths of 10, 30, 60, 120, or 400 cm at either 8, 10 or 12 mm width, these slings have a breaking strength of around 22 kN.
High-performance ropes for sailing and parasailing are made of Dyneema as well.
Recently developed additions to the US Military's Interceptor body armor, designed to offer arm and leg protection, are said to utilize a form of Spectra or Dyneema fabric.
It is also used in snowboards, often in combination with carbon fiber, reinforcing the fiberglass composite material, adding stiffness and improving its flex characteristics.
Dyneema is the preferred material for sport kite lines for two main reasons. First the low stretch means that control inputs to the kite are transferred quickly and secondly the low friction allows the kite to remain controllable up to about ten twists in the line.
Chemistry and properties
Dyneema fibers derive their strength from the extreme length of each individual molecule. The fibre can attain a parallel orientation greater than 95% and a level of crystallinity of up to 85%. In contrast, Kevlar derives its strength from strong bonding between relatively short molecules.
Its melting point is around 144 or 152 degrees Celsius, and according to DSM, it is not advisable to use Dyneema at temperatures exceeding 80 to 100 °C for long periods of time. It becomes brittle at temperatures below –150 °C. This contrasts strongly with other high-performance fibers, which tend to be quite heat-resistant.
The fibers feel slippery, similar to polypropylene and other hydrophobic fibers. Most people do not like the way Dyneema feels; for this reason, it is not often used in fabric. The slipperiness also makes such fibers less suitable for use in fibre reinforced plastics.
Another problem, in some applications, is that Dyneema will creep, meaning it will deform when placed under any long term stress. Like other olefins, it is very resistant to water, moisture, most chemicals, UV radiation, and micro-organisms.
Dyneema fibers are made using a DSM patented (1979) method called gel spinning. A precisely heated gel of UHMWPE is processed by an extruder through a spinneret. The extrudate is drawn through the air and then cooled in a water bath. The end result is a fiber with a high degree of molecular orientation, and therefore exceptional tensile strength.
To anneal UHMWPE the material should be heated to 135 - 138 °C in an oven or a liquid bath of silicone oil or glycerine. The material must then be cooled down at a rate of 5 °C / hour to at least 65 °C. Finally the material should be wrapped in an insulating blanket for 24 hours to bring to room temperature. 
PP ( Polypropylene )
Chemical name poly(1-methylethylene)
Synonyms Polypropylene; Polypropene;
Polipropene 25 [USAN];Propene polymers;
Propylene polymers; 1-Propene homopolymer
Chemical formula (C3H6)x
Monomer Propylene (Propene)
CAS number 9003-07-0 (atactic)
Density Amorphous: 0.85 g/cm3
Crystalline: 0.95 g/cm3
Melting point ~ 165 °C
temperature -10 °C
Degradation point 286 °C (559 K)
Disclaimer and references
Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flapPolypropylene or polypropene (PP) is a thermoplastic polymer, used in a wide variety of applications, including food packaging, textiles, plastic parts and reusable containers of various types, thermal pants and shirts made for the military, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. Its resin identification code is .
Chemical & physical properties
Most commercial polypropylene has an intermediate level of crystallinity between that of low density polyethylene (LDPE) and high density polyethylene (HDPE); its Young's modulus is also intermediate. Although it is less tough than HDPE and less flexible than LDPE, it is much more brittle than HDPE. This allows polypropylene to be used as a replacement for engineering plastics, such as ABS. Polypropylene is rugged, often somewhat stiffer than some other plastics, reasonably economical, and can be made translucent when uncolored but not completely transparent as polystyrene, acrylic or certain other plastics can be made. It can also be made opaque and/or have many kinds of colors. Polypropylene has very good resistance to fatigue, so that most plastic living hinges, such as those on flip-top bottles, are made from this material. Very thin sheets of polypropylene are used as a dielectric within certain high performance pulse and low loss RF capacitors.
Polypropylene has a melting point of 320 degrees Fahrenheit (160 degrees Celsius). Many plastic items for medical or laboratory use can be made from polypropylene which is autoclavable so that it can withstand the heat in an autoclave. Food containers made from it will not melt in the dishwasher, and do not melt during industrial hot filling processes. For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminium foil (both heat-resistant materials). After the product has cooled, the tubs are often given lids of a cheaper (and less heat-resistant) material, such as LDPE or polystyrene. Such containers provide a good hands-on example of the difference in modulus, since the rubbery (softer, more flexible) feeling of LDPE with respect to PP of the same thickness is readily apparent. Rugged, translucent, reusable plastic containers made in a wide variety of shapes and sizes for consumers from various companies such as Rubbermaid and Sterilite are commonly made of polypropylene, although the lids are often made of somewhat more flexible LDPE so they can snap on to the container to close it. When liquid, powdered, or similar consumer products come in disposable plastic bottles which do not need the improved properties of polypropylene, the containers are often made of slightly more economical polyethylene, although transparent plastics such as polyethylene terephthalate are also used for appearance. Plastic pails, car batteries, wastebaskets, cooler containers, dishes and pitchers are often made of polypropylene or HDPE, both of which commonly have rather similar appearance, feel, and properties at ambient temperature.
MFI (Melt Flow Index) identifies the flow speed of the raw material in the process. It helps to fill the plastic mold during the production process. The higher MFI increases, the weaker the raw material gets.
It also has Copolymer and Random Copolymer. Copolymer helps stiffness of the PP (Polypropylene). Random Copolymer helps transparent look.
Copolymer is more expensive than Homopolypropylene. Random Copolymer is even higher than copolymer PP.
A rubbery PP can also be made by a specialized synthesis process, as discussed below. Unlike traditional rubber, it can be melted and recycled, making it a thermoplastic elastomer.
Short segments of polypropylene, showing examples of isotactic (above) and syndiotactic (below) tacticity.An important concept in understanding the link between the structure of polypropylene and its properties is tacticity. The relative orientation of each methyl group (CH3 in the figure at left) relative to the methyl groups on neighboring monomers has a strong effect on the finished polymer's ability to form crystals, because each methyl group takes up space and constrains backbone bending.
Like most other vinyl polymers, useful polypropylene cannot be made by radical polymerization. The material that results from such a process has methyl groups arranged randomly, and so is called atactic. The lack of long-range order prevents any crystallinity in such a material, giving an amorphous material with very little strength and few redeeming qualities.
A Ziegler-Natta catalyst seems to be able to limit incoming monomers to a specific orientation, only adding them to the polymer chain if they face the right direction. Most commercially available polypropylene is made with titanium chloride catalysts, which produce mostly isotactic polypropylene (the upper chain in the figure above). With the methyl group consistenly on one side, such molecules tend to coil into a helical shape; these helices then line up next to one another to form the crystals that give commercial polypropylene its strength.
A ball-and-stick model of syndiotactic polypropylene.More precisely-engineered Kaminsky catalysts have been made, which offer a much greater level of control. Based on metallocene molecules, these catalysts use organic groups to control the monomers being added, so that a proper choice of catalyst can produce isotactic, syndiotactic, or atactic polypropylene, or even a combination of these. Aside from this qualitative control, they allow better quantitative control, with a much greater ratio of the desired tacticity than provious Ziegler-Natta techniques. They also produce higher molecular weights than traditional catalysts, which can further improve properties.
To produce a rubbery polypropylene, a catalyst can be made which yields isotactic polypropylene, but with the organic groups that influence tacticity held in place by a relatively weak bond. After the catalyst has produced a short length of polymer which is capable of crystallization, light of the proper frequency is used to break this weak bond, and remove the selectivity of the catalyst so that the remaining length of the chain is atactic. The result is a mostly amorphous material with small crystals embedded in it. Since each chain has one end in a crystal but most of its length in the soft, amorphous bulk, the crystalline regions serve the same purpose as vulcanization.
PS ( Polystyrene )
Density 1050 kg/m³
Electrical conductivity (σ) 10-16 S/m
Thermal conductivity 0.08 W/(m·K)
Young's modulus (E) 3000-3600 MPa
Tensile strength (σt) 46–60 MPa
Elongation at break 3–4%
Notch test 2–5 kJ/m²
Glass temperature 95 °C
Melting point 240 °C
Vicat B 90 °C
Heat transfer coefficient (λ) 0.17 W/(m²·K)
Linear expansion coefficient (α) 8 10-5 /K
Specific heat (c) 1.3 kJ/(kg·K)
Water absorption (ASTM) 0.03–0.1
Polystyrene is a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum. At room temperature, polystyrene is normally a solid thermoplastic, but can be melted at higher temperature for molding or extrusion, then resolidified. Styrene is an aromatic monomer, and polystyrene is an aromatic polymer.
Polystyrene was accidentally discovered in 1839 by Eduard Simon, an apothecary in Berlin, Germany. From storax, the resin of Liquidambar orientalis, he distilled an oily substance, a monomer which he named styrol. Several days later Simon found that the styrol had thickened, presumably due to oxidation, into a jelly he dubbed styrol oxide ("Styroloxyd"). By 1845 English chemist John Blyth and German chemist August Wilhelm von Hofmann showed that the same transformation of styrol took place in the absence of oxygen. They called their substance metastyrol. Analysis later showed that it was chemically identical to Styroloxyd. In 1866 Marcelin Berthelot correctly identified the formation of metastyrol from styrol as a polymerization process. About 80 years went by before it was realized that heating of styrol starts a chain reaction which produces macromolecules, following the thesis of German organic chemist Hermann Staudinger (1881 - 1965). This eventually led to the substance receiving its present name, polystyrene. The I.G. Farben company began manufacturing polystyrene in Ludwigshafen, Germany, about 1931, hoping it would be a suitable replacement for die cast zinc in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a heated tube and cutter, producing polystyrene in pellet form.
Pure solid polystyrene is a colorless, hard plastic with limited flexibility. It can be cast into molds with fine detail. Polystyrene can be transparent or can be made to take on various colors. It is economical and is used for producing plastic model assembly kits, plastic cutlery, CD "jewel" cases, and many other objects where a fairly rigid, economical plastic of any of various colors is desired.
Polystyrene packaging materialPolystyrene's most common use, however, is as expanded polystyrene (EPS). Expanded polystyrene is produced from a mixture of about 90-95% polystyrene and 5-10% gaseous blowing agent, most commonly pentane or carbon dioxide . The solid plastic is expanded into a foam through the use of heat, usually steam. Extruded polystyrene (XPS), which is different from expanded polystyrene, is commonly known by the trade name Styrofoam. The voids filled with trapped air give it low thermal conductivity. This makes it ideal as a construction material and it is used in structural insulated panel building systems. It is also used as insulation in building structures, as molded packing material for cushioning fragile equipment inside boxes, as packing "peanuts", as non-weight-bearing architectural structures (such as pillars), and also in crafts and model building, particularly architectural models. Foamed between two sheets of paper, it makes a more-uniform substitute for corrugated cardboard, tradenamed Fome-Cor.
Expanded polystyrene used to contain CFCs, but other, more environmentally-safe blowing agents are now used. Because it is an aromatic hydrocarbon, it burns with an orange-yellow flame, giving off soot, as opposed to non-aromatic hydrocarbon polymers such as polyethylene, which burn with a light yellow flame (often with a blue tinge) and no soot.
Production methods include sheet stamping (PS) and injection molding (both PS and HIPS).
The chemical makeup of polystyrene is a long chain hydrocarbon with every other carbon connected to a Phenyl group (an aromatic ring similar to benzene).
A 3-D model would show that each of the chiral backbone carbons lies at the center of a tetrahedron, with its 4 bonds pointing toward the vertices. Say the -C-C- bonds are rotated so that the backbone chain lies entirely in the plane of the diagram. From this flat schematic, it isn't evident which of the phenyl (benzene) groups are angled toward us from the plane of the diagram, and which ones are angled away. The isomer where all of them are on the same side is called isotactic polystyrene, which isn't produced commercially. Ordinary atactic polystyrene has these large phenyl groups randomly distributed on both sides of the chain. This random positioning prevents the chains from ever aligning with sufficient regularity to achieve any crystallinity, so the plastic has no melting temperature, Tm. But metallocene-catalyzed polymerization can produce an ordered syndiotactic polystyrene with the phenyl groups on alternating sides. This form is highly crystalline with a Tm of 270°C.
The resin identification code symbol for polystyrene, developed by the Society of the Plastics Industry so that items can be labeled for easy recycling, is . Unfortunately, the majority of polystyrene products are currently not recycled due to a lack of suitable recycling facilities. Furthermore, when it is "recycled," it is not a closed loop — polystyrene cups and other packaging materials are usually recycled into fillers in other plastics, or other items that cannot themselves be recycled and are thrown away.
The Unicode character is U+2678, which will appear here if you have a suitable font installed.
Pure polystyrene is brittle, but hard enough that a fairly high-performance product can be made by giving it some of the properties of a stretchier material, such as polybutadiene rubber. The two such materials can never normally be mixed due to the amplified effect of intermolecular forces on polymer insolubility (see plastic recycling), but if polybutadiene is added during polymerization it can become chemically bonded to the polystyrene, forming a graft copolymer which helps to incorporate normal polybutadiene into the final mix, resulting in high-impact polystyrene or HIPS, often called "high-impact plastic" in advertisements. One commercial name for HIPS is Bextrene. Common applications include use in toys and product casings. HIPS is usually injection molded in production. Autoclaving polystyrene can compress and harden the material.
Acrylonitrile butadiene styrene or ABS plastic is similar to HIPS: a copolymer of acrylonitrile and styrene, toughened with polybutadiene. Most electronics cases are made of this form of polystyrene, as are many sewer pipes.
Styrene can be copolymerized with other monomers; for example, divinylbenzene for cross-linking the polystyrene chains.
Cutting and shaping
Expanded polystyrene is very easily cut with a hot-wire foam cutter, which is easily made by a heated and taut length wire, usually nichrome due to nichrome's resistance to oxidation at high temperatures and its suitable electrical conductivity. The hot wire foam cutter works by heating the wire to the point where it can vaporize foam immediately adjacent to it. The foam gets vaporized before actually touching the heated wire, which yields exceptionally smooth cuts.
Polystyrene, shaped and cut with hot wire foam cutters, is used in architecture models, actual signage, amusement parks, movie sets, airplane construction, and much more. Such cutters may cost just a few dollars (for a completely manual cutter) to tens of thousands of dollars for large CNC machines that can be used in high-volume industrial production.
Polystyrene can also be cut with a traditional cutter, in order to do this without ruining the sides one must first dip the blade in water and cut with the blade at an angle of about 30º, the procedure has to be repeated multiple times for best results.
Polystyrene is also able to be cut on 3 and 5-axis routers, enabling large scale prototyping and model making to be accomplished. Special polystyrene cutters are available that look more like large cylindrical rasps.
Use in biology
Petri dishes and other containers such as test tubes, made of polystyrene, play an important role in biomedical research and science. For these uses, articles are almost always made by injection molding, and often sterilized post molding, either by irradiation or treatment with ethylene oxide. Post mold surface modification, usually with oxygen rich plasmas, is often done to introduce polar groups. Much of modern biomedical research relies on the use of such products; they therfore play a critical role in pharmaceutical research. Major manufactueres include Corning/Costar, Nalgene/Nunc, Greiner and BD/Falcon. The web sites of these companies contain a wealth of information.
In the United States, environmental protection regulations prohibit the use of solvents on polystyrene (which would dissolve the polystyrene and de-foam most of foams anyway).
Some acceptable finishing materials are
Water-based paint (artists have created paintings on polystyrene with gouache)
Mortar or acrylic/cement render, often used in the building industry as a weather-hard overcoat that hides the foam completely after finishing the objects.
Cotton wool or other fabrics used in conjunction with a stapling implement.
Dangers and Fire hazard
The health effects caused by consuming Polystyrene (PS) when it migrates from food containers (primarily due to a leaching caused by heat exchange) into food is under serious investigation. Although the EPA has not yet come to a definitive conclusion on the direct carcinogenic effects of PS, the evidence is mounting. Benzene (a material used in the production of PS) is a known human carcinogen. Moreover, Butadiene and Styrene (basic building blocks of PS), when combined, they become benzene-like in both form and function. For this reason PS is highly suspected to be carcinogenic in the same manner as benzene, although the jury is still out due to a lack of controlled studies.
Polystyrene is classified according to DIN4102 as a "B3" product, meaning highly flammable or "easily ignited". Consequently, though it is an efficient insulator at low temperatures, it is prohibited from being used in any exposed installations in building construction. It must be concealed behind drywall, sheet metal or concrete. Foamed plastic materials have been accidentally ignited and caused huge fires and losses. Examples include the Düsseldorf International Airport, the Channel tunnel, where it was inside a railcar and caught on fire, and the Browns Ferry nuclear plant, where fire reached through a fire retardant, reached the foamed plastic underneath, inside a firestop that did not consider bounding.
In addition to fire hazard, substances that contain Acetone (such as most Aerosol paint sprays) and Cyanoacrylate glues can cause polystyrene foam to melt.
Polystyrene is used in some polymer-bonded explosives:
Some Polystyrene PBX Examples Name Explosive Ingredients Binder Ingredients Usage
PBX-9205 RDX 92% Polystyrene 6%; DOP 2%
PBX-9007 RDX 90% Polystyrene 9.1%; DOP 0.5%; rosin 0.4%
PET ( Polyethylene terephthalate )
Density 1370 kg/m3
Young's modulus(E) 2800–3100 MPa
Tensile strength(σt) 55–75 MPa
Elongation @ break 50–150%
notch test 3.6 kJ/m2
Glass temperature 75 °C
melting point 260 °C
Vicat B 170 °C
Thermal conductivity 0.24 W/m.K
linear expansion coefficient (α) 7×10−5/K
Specific heat (c) 1.0 kJ/kg.K
Water absorption (ASTM) 0.16
Price 0.5–1.25 €/kg
Polyethylene terephthalate (aka PET, PETE or the obsolete PETP or PET-P) is a thermoplastic polymer resin of the polyester family that is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber. It is one of the most important raw materials used in man-made fibers.
Depending on its processing and thermal history, it may exist both as an amorphous (transparent) and as a semi-crystalline (opaque and white) material. Its monomer can be synthesized by the esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct or the transesterification reaction between ethylene glycol and dimethyl terephthalate with methanol as a byproduct. Polymerization is through a polycondensation reaction of the monomers (done immediately after esterification/transesterification) with ethylene glycol as the byproduct (the ethylene glycol is recycled in production).
The majority of the world's PET production is for synthetic fibers (in excess of 60%) with bottle production accounting for around 30% of global demand. In discussing textile applications, PET is generally referred to as simply "polyester" while "PET" is used most often to refer to packaging applications.
It is manufactured under trade names Arnite, Impet and Rynite, Ertalyte, Hostaphan, Melinex and Mylar films, and Dacron, Terylene & Trevira fibers.
A PET soft drink bottle
Sails are usually made of Dacron, a brand of PET fiber; colorful lightweight spinnakers are usually made of nylon.PET can be semi-rigid to rigid, depending on its thickness, and is very lightweight. It makes a good gas and fair moisture barrier, as well as a good barrier to alcohol (requires additional "Barrier" treatment) and solvents. It is strong and impact-resistant. It is naturally colorless and transparent.
When produced as a thin film (often known by the tradename Mylar), PET is often coated with aluminium to reduce its permeability, and to make it reflective and opaque. PET bottles are excellent barrier materials and are widely used for soft drinks, (see carbonation). PET or Dacron is also used as a thermal insulation layer on the outside of the International Space Station as seen in an episode of Modern Marvels "Sub Zero". For certain specialty bottles, PET sandwiches an additional polyvinyl alcohol to further reduce its oxygen permeability.
When filled with glass particles or fibers, it becomes significantly stiffer and more durable. This glass-filled plastic, in a semi-crystalline formulation, is sold under the tradename Rynite.
While all thermoplastics are technically recyclable, PET bottle recycling is more practical than many other plastic applications. The primary reason is that plastic carbonated soft drink bottles and water bottles are almost exclusively PET which makes them more easily identifiable in a recycle stream. PET has a resin identification code of 1. PET, as with many plastics, is also an excellent candidate for thermal recycling (incineration) as it is composed of carbon, hydrogen and oxygen with only trace amounts of catalyst elements (no sulfur) and has the energy content of soft coal.
One of the most important characteristics of PET is referred to as I.V.(intrinsic viscosity). The I.V. of the material, measured in dl/g (deciliters/gram) is dependent upon the length of its polymer chains. The longer the chains, the stiffer the material, and therefore the higher the I.V. The average chain length of a particular batch of resin can be controlled during polymerization.
An I.V. of about:
0.60 - Would be appropriate for fiber
0.65 - Film
0.76-0.84 - Bottles
0.85 - Tire cord
PET is hygroscopic, meaning that it naturally absorbs water from its surroundings. However when this 'damp' PET is then heated a chemical reaction known as hydrolysis takes place between the water and the PET which reduces its molecular weight (IV) and its physical properties. This means that before the resin can be processed in a molding machine, as much moisture as possible must be removed from the resin. This is achieved through the use of a desiccant.
Inside the dryer, hot dry air is pumped into the bottom of the hopper containing the resin so that it flows up through the pellets removing moisture on its way. The hot wet air leaves the top of the hopper and is first run through an after-cooler, because it is easier to remove moisture from cold air than hot air. The resulting cool wet air is then passed through a desiccant bed. Finally the cool dry air leaving the desiccant bed is re-heated in a process heater and sent back through the same processes in a closed loop. Typically residual moisture levels in the resin must be less than 40 ppm before processing. Dryer residence time should not be shorter than about four hours. This is because drying the material in less than 4 hours would require a temperature above 160 °C, at which level hydrolysis would begin inside the pellets before they could be dried out.
In addition to pure (homopolymer) PET, PET modified by copolymerization is also available.
In some cases, the modified properties of copolymer are more desirable for a particular application. For example, cyclohexane dimethanol (CHDM) can be added to the polymer backbone in place of ethylene glycol. Since this building block is much larger (6 additional carbon atoms) than the ethylene glycol unit it replaces, it does not fit in with the neighboring chains the way an ethylene glycol unit would. This interferes with crystallization and lowers the polymer's melting temperature.
Replacing terephthalic acid (right) with isophthalic acid (center) creates a kink in the PET chain, interfering with crystallization and lowering the polymer's melting point.Another common modifier is isophthalic acid, replacing some of the 1,4- (para-) linked terephthalate units. The 1,2- (ortho-) or 1,3- (meta-) linkage produces an angle in the chain, which also disturbs crystallinity.
PVC ( Polyvinyl chloride )
Density 1380 kg/m3
Young's modulus (E) 2900-3400 MPa
Tensile strength(σt) 50-80 MPa
Elongation @ break 20-40%
Notch test 2-5 kJ/m2
Glass temperature 87 °C
Melting point 212 °C
Vicat B1 85 °C
Heat Transfer Coefficient (λ) 0.16 W/m.K
Linear Expansion Coefficient (α) 8 10-5 /K
Specific heat (c) 0.9 kJ/(kg·K)
Water absorption (ASTM) 0.04-0.4
Polyvinyl chloridePolyvinyl chloride, (IUPAC über Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. In terms of revenue generated, it is one of the most valuable products of the chemical industry. Globally, over 50% of PVC manufactured is used in construction. As a building material, PVC is cheap and easy to assemble. In recent years, PVC has been replacing traditional building materials such as wood, concrete and clay in many areas. Despite appearing to be an ideal building material, concerns were raised about the costs of PVC to the natural environment and human health.
There are many uses for PVC. As a hard plastic, it is used as vinyl siding, magnetic stripe cards, window profiles, gramophone records (which is the source of the name for vinyl records), pipe, plumbing and conduit fixtures. It can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates. In this form, it is used in clothing and upholstery, and to make flexible hoses and tubing, flooring, to roofing membranes, and electrical cable insulation. The material is often used for pipelines in the water and sewer industries because of its inexpensive nature and flexibility.
Polyvinyl chloride is produced by polymerization of the monomer vinyl chloride, as shown.
Polyvinyl chloride was accidentally discovered on at least two different occasions in the 19th century, first in 1835 by Henri Victor Regnault and in 1872 by Eugen Baumann. On both occasions, the polymer appeared as a white solid inside flasks of vinyl chloride that had been left exposed to sunlight. In the early 20th century, the Russian chemist Ivan Ostromislensky and Fritz Klatte of the German chemical company Griesheim-Elektron both attempted to use PVC (Polyvinyl Chloride) in commercial products, but difficulties in processing the rigid, sometimes brittle polymer blocked their efforts. In 1926, Waldo Semon of B.F. Goodrich developed a method to plasticize PVC by blending it with various additives. The result was a more flexible and more easily processed material that soon achieved widespread commercial use.
PVC is commonly used as the insulation on electric wires; the plastic used for this purpose needs to be plasticized. In a fire, PVC-coated wires can form HCl fumes; the chlorine serves to scavenge free radicals and is the source of the material's fire retardance. However, these (intentional) fumes can also pose a health hazard in their own right. Frequently in applications where smoke is a major hazard (notably in tunnels) PVC-free LSOH (low-smoke, zero-halogen) cable insulation is used.
Polyvinylchloride is also widely used for producing pipes. About 90% of all PVC pipes are used for drainage and for protecting/containing cables in buildings
Unplasticized polyvinyl chloride (uPVC)
Modern "Tudorbethan" house with uPVC gutters and downpipes, fascia, decorative imitation "half-timbering", windows and doors.uPVC is often used in the building industry as a low maintenance material, particularly in the UK, and in the USA where it is known as vinyl.The material comes in a range of colours and finishes, including a photo-effect wood finish, and is used as a substitute for painted wood, most obviously for window frames and sills when installing double glazing in new buildings or to replace older single glazed windows. It has many other uses including fascia, and siding or weatherboarding. The same material has almost entirely replaced the use of cast iron for plumbing and drainage, being used for waste pipes, drainpipes, gutters and downpipes.
Due to environmental concerns use of PVC is discouraged by some local and authoritiesand in countries such as Germany and The Netherlands.
Health and safety
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Many vinyl products contain additional chemicals to change the chemical consistency of the product. Some of these additional chemicals called additives can leach out of vinyl products. Plasticizers which must be added to make PVC flexible have been an additive of particular concern.
Because soft PVC toys have been made for babies for years, there are concerns that these additives leach out of soft toys into the mouths of the children chewing on them. Vinyl IV bags used in neo-natal intensive care units have also been shown to leach DEHP (Bis(2-ethylhexyl) phthalate), a phthalate additive. In January 2006, the European Union to placed a ban on six types of phthalate softeners in toys (See directive 2005/84/EC). In 2003, the US Consumer Product Safety Commission (CPSC) denied a petition for a similar ban in the United States however, in the USA most companies have voluntarily stopped manufacturing PVC toys for this age group or have eliminated the phthalates. In a draft guidance paper published in September 2002, the US FDA recognizes that many medical devices with PVC containing DEHP are not used in ways that result in significant human exposure to the chemical. However, FDA is suggesting that manufacturers consider eliminating the use of DEHP in certain devices that can result in high aggregate exposures for sensitive patient populations such as neonates. However, alternative softeners have not been properly tested to determine whether they are more or less safe. Other vinyl products, including car interiors, shower curtains, flooring, etc., initially release chemical gases into the air. Some studies indicate that this outgassing of additives may contribute to health complications, but this information is preliminary and further study is needed.
According to MIT professor Dr. Makhlook Singh, the properties of PVC may be useful for biological applications as well. He noted the fungi Indiamycetes seems to bond well with the surface of PVC and begins to break down the carbon chains of the PVC. The fungus soon dies, but it leaves behind a toxin resin coating that has been shown to reduce Concentrations of many types of bacteria. He is excited about new pharachological use of this resin. However, further tests will be needed to determine the usefulness of this toxic resin.
According to some medical studies, the plasticizers added to PVC may cause chronic conditions such as scleroderma, cholangiocarcinoma, angiosarcoma, brain cancer, and acroosteolysis. PVC has been used in many products for many years and still there is not proof of significant harmful effects from exposure. There have been studies, some cited in this article, that indicate links with certain medical problems and exposure to PVC products.
In 2004, a joint Swedish-Danish research team found a very strong link between allergies in children and the phthalates DEHP and BBzP, commonly used in PVC.Alternative plasticisers are being developed but in many cases these alternatives remain significantly more expensive and their technical performance varies. It is also worth noting that some, though not all, of the alternatives pose significant health risks.
In November 2005, one of the largest hospital networks in the U.S., Catholic Healthcare West, signed a contract with B.Braun for vinyl-free intravenous bags and tubing. According to the Center for Health, Environment & Justice in Falls Church, VA, which helps to coordinate a "precautionary" "PVC Campaign", a slew of major corporations including Microsoft, Wal-Mart, and Kaiser Permanente announced efforts to eliminate PVC from products and packaging in 2005.
Vinyl chloride monomer
In the late 1960s, Dr. John Creech and Dr. Maurice Johnson were the first to clearly link and recognize the carcinogenicity of vinyl chloride monomer to humans when workers in the polyvinyl chloride polymerization section of a B.F. Goodrich plant near Louisville, Kentucky, were diagnosed with liver angiosarcoma, a rare disease.Since that time, studies of PVC workers in Australia, Italy, Germany, and the UK have all associated certain types of occupational cancers with exposure to vinyl chloride. The link between angiosarcoma of the liver and long-term exposure to vinyl chloride is the only one which has been confirmed by the International Agency for Research on Cancer. All the cases of angiosarcoma developed from exposure to vinyl chloride monomer, were in workers who were exposed to very high VCM levels, routinely, for many years.
According to the EPA, "vinyl chloride emissions from polyvinyl chloride (PVC), ethylene dichloride (EDC), and vinyl chloride monomer (VCM) plants cause or contribute to air pollution that may reasonably be anticipated to result in an increase in mortality or an increase in serious irreversible, or incapacitating reversible illness. Vinyl chloride is a known human carcinogen which causes a rare cancer of the liver."
A front-page series in the Houston Chronicle claimed the vinyl industry has manipulated vinyl chloride studies to avoid liability for worker exposure and to hide extensive and severe chemical spills into local communities.
The environmentalist group Greenpeace has advocated the global phase-out of PVC because they claim dioxin is produced as a byproduct of vinyl chloride manufacture and from incineration of waste PVC in domestic garbage. The European Industry, however, asserts that it has improved production processes to minimize dioxin emissions. Dioxins are a global health threat because they persist in the environment and can travel long distances. At very low levels, near those to which the general population is exposed, dioxins have been linked to immune system suppression, reproductive disorders, a variety of cancers, and endometriosis. According to a 1994 report by the British firm, ICI Chemicals & Polymers Ltd., "It has been known since the publication of a paper in 1989 that these oxychlorination reactions [used to make vinyl chloride and some chlorinated solvents] generate polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs). The reactions include all of the ingredients and conditions necessary to form PCDD/PCDFs.... It is difficult to see how any of these conditions could be modified so as to prevent PCDD/PCDF formation without seriously impairing the reaction for which the process is designed." In other words, dioxins are an unavoidable consequence of making PVC. Dioxins created by vinyl chloride production are released by on-site incinerators, flares, boilers, wastewater treatment systems and even in trace quantities in vinyl resins. The US EPA estimate of dioxin releases from the PVC industry (based on industry estimates) more than doubled between 1995 and 2000.
The largest well-quantified source of dioxin in the US EPA inventory of dioxin sources is barrel burning of household waste. Studies of household waste burning indicate consistent increases in dioxin generation with increasing PVC concentrations.According to the EPA dioxin inventory, landfill fires are likely to represent an even larger source of dioxin to the environment. A survey of international studies consistently identifies high dioxin concentrations in areas affected by open waste burning and a study that looked at the homologue pattern found the sample with the highest dioxin concentration was “typical for the pyrolysis of PVC”. Other EU studies indicate that PVC likely “accounts for the overwhelming majority of chlorine that is available for dioxin formation during landfill fires.”
The next largest sources of dioxin in the EPA inventory are medical and municipal waste incinerators. Studies have shown a clear correlation between dioxin formation and chloride content and indicate that PVC is a significant contributor to the formation of both dioxin and PCB in incinerators.
PVC is not typically recycled due to the prohibitive cost of regrinding and recompounding the resin compared to the cost of virgin (unrecycled) resin.
The thermal depolymerization process can safely and efficiently convert PVC into fuel and minerals, according to the company that developed it. It is not yet in widespread use.
ABS ( Acrylonitrile butadiene styrene )
Acrylonitrile butadiene styrene
Monomers in ABS polymerAcrylonitrile butadiene styrene, or ABS, (chemical formula (C8H8· C4H6·C3H3N)x) is a common thermoplastic used to make light, rigid, molded products such as pipes, golf club heads (used for its good shock absorbance), automotive body parts, wheel covers, enclosures, protective head gear, and toys including LEGO bricks. It is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15% to 35% acrylonitrile, 5% to 30% butadiene and 40% to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly(styrene-co-acrylonitrile). The nitrile groups from neighbouring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures. ABS can be used between −25 °C and 60 °C.
Production of 1 kg of ABS requires the equivalent of about 2 kg of oil for raw materials and energy. It can also be recycled.
Acrylonitrile butadiene styrene can be found as a graft copolymer, in which styrene-acrylonitrile polymer is formed in a polymerization system in the presence of polybutadiene rubber latex; the final product is a complex mixture consisting of styrene-acrylonitrile copolymer, a graft polymer of styrene-acrylonitrile and polybutadiene and some unchanged polybutadiene rubber. There are, therefore, many variables to the process besides the different positions of the starting materials, so this technique is capable of producing polymers with a much wider range of properties.ABS can be made by blending, the technique involved mechanical blending by mixing a butadiene-acrylonitrile rubber with styrene-acrylonitrile resins, the process is being carried out under such conditions that the two polymers underwent some grafting. This technique is rather limited and has been largely suppressed by chemical process.
ABS is derived from acrylonitrile, butadiene, and styrene. Where acrylonitrile are synthetic monomers produced from propylene and ammonia; butadiene is a petroleum hydrocarbon obtained from butane; and styrene monomers, derived from coal, are commercially obtained from benzene and ethylene from coal. The advantage of ABS is that this material combines the strength and rigidity of the acrylonitrile and styrene polymers with the toughness of the polybutadiene rubber. The most amazing mechanical properties of ABS are resistance and toughness. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance. The impact resistance can be amplified by increasing the proportions of polybutadiene in relation to styrene and acrylonitrile although this causes changes in other properties. Impact resistance does not fall off rapidly at lower temperatures. Stability under load is excellent with limited loads.
Even though ABS plastics are used largely for mechanical purposes, they also have good electrical properties that are fairly constant over a wide range of frequencies. These properties are little affected by temperature and atmospheric humidity in the acceptable operating range of temperatures. The final properties will be influenced to some extent by the conditions under which the material is processed to the final product; for example, molding at a high temperature improves the gloss and heat resistance of the product whereas the highest impact resistance and strength are obtained by molding at low temperature.
ABS polymers are resistant to aqueous acids, alkalis, concentrated hydrochloric and phosphoric acids, alcohols and animal, vegetable and mineral oils, but they are swollen by glacial acetic acid, carbon tetrachloride and aromatic hydrocarbons and are attacked by concentrated sulfuric and nitric acids. They are soluble in esters, ketones and ethylene dichloride.
The aging characteristics of the polymers are largely influenced by the polybutadiene content, and it is normal to include antioxidants in the composition. On the other hand, the cost of producing ABS is roughly twice the cost of producing polystyrene, ABS is considered superior for its hardness, gloss, toughness, and electrical insulation properties. However, it will be degraded when exposed to acetone.
PA ( POLYAMIDE )
A polyamide is a polymer containing monomers joined by peptide bonds. They can occur both naturally, examples being proteins, such as wool and silk, and can be made artificially, examples being Nylon, Kevlar and sodium poly(aspartate).
Production from monomers
The amide link is produced from the condensation reaction of an amino group and a carboxylic acid or acid chloride group. A small molecule, usually water, ammonia or hydrogen chloride, is eliminated.
The amino group and the carboxylic acid group can be on the same monomer, or the polymer can be constituted of two different bifunctional monomers, one with two amino groups, the other with two carboxylic acid or acid chloride groups.
Amino Acids can be taken as examples of single monomer (if the difference between R groups is ignored) reacting with identical molecules to form a polyamide:
The reaction of two amino acids. Many of these reactions produce long chain proteins
Kevlar is made from two different monomers which continuously alternate to form the polymer:
The reaction of 1,4-phenyl-diamine (para-phenylenediamine) and terephthaloyl chloride to produce Kevlar.
PC ( Polycarbonate )
Density (ρ) 1200-1220 kg/m³
Abbe number (V) 34.0
Refractive index (n) 1.584-6
Limiting oxygen index 25-27%
Water absorption - Equilibrium(ASTM) 0.16-0.35%
Water absorption - over 24 hours 0.1%
Radiation resistance Fair
Ultraviolet (1-380nm) resistance Fair
Young's modulus (E) 2-2.4 GPa
Tensile strength (σt) 55-75 MPa
Compressive strength (σc) >80 MPa
Elongation (ε) @ break 80-150%
Poisson's ratio (ν) 0.37
Hardness - Rockwell M70
Izod impact strength 600-850 J/m
Notch test 20-35 kJ/m²
Abrasive resistance - ASTM D1044 10-15 mg/1000 cycles
Coefficient of friction (μ) 0.31
Melting temperature (Tm) 267°C*
Glass transition temperature(Tg) 150°C
Heat Deflection Temperature - 10 kN (Vicat B)<1> 145°C
Heat Deflection Temperature - 0.45 MPa 140°C
Heat Deflection Temperature - 1.8 MPa 128-138°C
Upper working temperature 115-130°C
Lower working temperature -135°C
Linear thermal expansion coefficient (α) 65-70 × 10-6/K
Specific heat capacity (c) 1.2-1.3 kJ/kg·K
Thermal conductivity (k) @ 23°C 0.19-0.22 W/(m·K)
Heat transfer coefficient (h) 0.21 W/(m²·K)
Dielectric constant (εr) @ 1 MHz 2.9
Permittivity (ε) @ 1 MHz 2.568 x10-11 F/m
Relative Permeability (μr) @ 1 MHz 0.866(2)
Permeability (μ) @ 1 MHz 1.089(2) μN/A²
Dielectric strength 15-67 kV/mm
Dissipation factor @ 1 MHz 0.01
Surface Resistivity 1015 Ω/sq
Volume Resistivity (ρ) 1012-1014 Ω·m
Near to Short-wave Infrared Transmittance Spectrum
Polycarbonate transmittance in 5/6 of the NIR & 1/5 of the SWIR regions. Also, polycarbonate is almost completely transparent throughout the entire visible region of the spectrum and very sharply cuts off to ~0% transmission at almost exactly 400 nm, blocking all UV light transmission.
Acids - concentrated Poor
Acids - dilute Good
Aromatic hydrocarbons Poor
Greases & Oils Good-Fair
Halogenated Hydrocarbons Good-Poor
Polycarbonates are a particular group of thermoplastic polyesters. They are easily worked, molded, and thermoformed; as such, these plastics are very widely used in modern manufacturing. Their interesting features (temperature resistance, impact resistance and optical properties) positions them between commodity plastics and engineering plastics.
Polycarbonates got their name because they are polymers having functional groups linked together by carbonate groups (-O-(C=O)-O-) in a long molecular chain. Also carbon monoxide was used as a C1-synthon on an industrial scale to produce diphenyl carbonate, being later trans-esterificated with a diphenolic derivative affording poly(aromatic carbonate)s. Taking into consideration the C1-synthon we can divide polycarbonates into poly(aromatic carbonate)s and poly(aliphatic carbonate)s. The second one, poly(aliphatic carbonate)s are a product of the reaction of carbon dioxide with epoxides, which owing to the thermodynamical stability of carbon dioxide requires the use of catalyst. The working systems are based on porphyrins, alkoxides, carboxylates, salens and beta-diiminates as organic, chelating ligands and aluminium, zinc, cobalt and chromium as the metal centres. Poly(aliphatic carbonate)s display promising characteristics, have a better biodegradability than the aromatic ones and could be employed to develop other specialty polymers.
The most common type of polycarbonate plastic is one made from bisphenol A, in which groups from bisphenol A are linked together by carbonate groups in a polymer chain. This polycarbonate is characterized as a very durable material, and can be laminated to make bullet-proof "glass", though “bullet-resistant” would be more accurate. Although polycarbonate has high impact-resistance, it has low scratch-resistance and so a hard coating is applied to polycarbonate eye-wear lenses. The characteristics of polycarbonate are quite like those of polymethyl methacrylate (PMMA; acrylic), but polycarbonate is stronger and more expensive. This polymer is highly transparent to visible light and has better light transmission characteristics than many kinds of glass. CR-39 is a specific polycarbonate material mdash; although it is usually referred to as CR-39 plastic — with good optical and mechanical properties, frequently used for eyeglass lenses.
Polycarbonate has :
a density of 1.20 g/cm3
a use range from −100 °C to +135 °C
a melting point around 250 °C
a refractive index equal to 1.585 ± 0.001
a light transmission index equal to 90% ± 1%
poor weathering in an ultraviolet (UV) light environment
Main transformation techniques for Polycarbonate resins are:
injection moulding into ready articles
extrusion into tubes, rods and other profiles
extrusion with calenders into sheet (1-15 mm) and film (below 1 mm), which can be used as such, or manufactured into other shapes using thermoforming or secondary fabrication techniques, such as bending, drilling, routing, laser cutting etc.
Polycarbonate is becoming more common in housewares as well as laboratories and in industry, mainly where at least two of its three main features are required: high impact resistance, temperature resistance and optical properties. Typical injected applications are : lighting lenses sunglass/eyeglass lenses, compact discs, DVDs, automotive headlamp lenses, Nalgene bottles. It is also used for animal enclosures and cages used in research...
Typical sheet/film applications are:
Industry: machined or formed, cases, machine glazing, riot shields, visors, instrument panels
Advertisement: Signs, displays, poster protection
Building : domelights, flat or curved glazing, sound walls,
Remark : for use in applications exposed to weathering or UV-radiation, a special surface treatment is needed. This either can be a coating (e.g. for improved abrasion resistance), or a coextrusion for enhanced weathering resistance.
Most common resins are LEXAN® from General Electric, CALIBRE® from DOW Chemicals, MAKROLON® from Bayer and PANLITE® from Teijin Chemical Limited. As being based on bisphenol A, and phenol based on benzene, pricing is much depending on phenol and benzene pricing.
Potential hazards in food contact applications
Polycarbonate may be appealing to fabricators and purchasers of food storage containers due to its clarity and toughness. Polycarbonate has been described as lightweight and highly break resistant particularly when compared to silica glass. Polycarbonate may be seen in the form of single use and refillable plastic water bottles.
More than 100 studies have explored the bioactivity of bisphenol A leachates from polycarbonates. Bisphenol A appeared to be released from polycarbonate animal cages into water at room temperature and that it may have been responsible for enlargement of the reproductive organs of female mice.
An analysis of the literature on bisphenol A leachate low-dose effects by vom Saal and Hughes published in August 2005 seems to have found a suggestive correlation between the source of funding and the conclusion drawn. Industry funded studies tend to find no significant effects while government funded studies tend to find significant effects.
One point of agreement among those studying polycarbonate water and food storage containers may be that using sodium hypochlorite bleach and other alkali cleaners to clean polycarbonate is not recommended, as they catalyze the release of the Bisphenol-A. The tendency of polycarbonate to release bisphenol A was discovered after a lab tech used strong cleaners on polycarbonate lab containers. Endocrine disruption later observed on lab rats was traced to exposure from the cleaned containers.
A chemical compatibility chart shows reactivity between chemicals such as polycarbonate and a cleaning agent. Alcohol is one recommended organic solvent for cleaning grease and oils from polycarbonate.For treating mold, Borax:H2O 1:96 to 1:8 may be effective.
Polycarbonate can be synthesized from bisphenol A and phosgene (carbonyl dichloride, COCl2). The first step in the synthesis of polycarbonate from bisphenol A is treatment of bisphenol A with sodium hydroxide. This deprotonates the hydroxyl groups of the bisphenol A molecule.
The deprotonated oxygen reacts with phosgene through carbonyl addition to create a tetrahedral intermediate (not shown here), after which the negatively charged oxygen kicks off a chloride ion (Cl-) to form a chloroformate.
The chloroformate is then attacked by another deprotonated bisphenol A, eliminating the remaining chloride ion and forming a dimer of bisphenol A with a carbonate linkage in between.
Repetition of this process yields polycarbonate, a polymer with alternating carbonate groups and groups from bisphenol A. Density starts at about 1.20 g/cm³
PMMA ( Polymethyl methacrylate )
Chemical name poly (methyl 2-methylpropenoate)
Chemical formula (C5O2H8)n
poly (methyl methacrylate)
methyl methacrylate resin
Molecular mass varies
CAS number 9011-14-7
Density 1.19 g/cm³
Melting point 130-140°C (265-285°F)
Boiling point 200.0 °C
Refractive index 1.492 (λ=589.3 nm)
Disclaimer and references
Polymethyl methacrylate (PMMA) or poly (methyl 2-methylpropenoate) is the synthetic polymer of methyl methacrylate. This thermoplastic and transparent plastic is sold by the tradenames Plexiglas, Perspex, Plazcryl, Acrylite, Acrylplast, Altuglas, and Lucite and is commonly called acrylic glass or simply acrylic. The material was developed in 1928 in various laboratories and was brought to market in 1933 by Rohm and Haas Company.
The material is often used as an alternative to glass. Differences in the properties of the two materials include:
PMMA is less dense; its density can range from 1150-1190 kg/m3. This is less than half the density of glass which ranges 2400 to 2800 kg/m3.
PMMA has a higher impact strength than glass and will not shatter.
PMMA is softer and more easily scratched than glass. This can be overcome with scratch-resistant coatings.
PMMA is typically processed at 240-250 degrees Celsius.
PMMA transmits more light (up to 93% of visible light) than glass.
Unlike glass, PMMA does not filter ultraviolet (UV) light. PMMA transmits UV light, at best intensity, down to 300 nm. Some manufacturers coat their PMMA with UV films to add this property. On the other hand, PMMA molecules have great UV stability compared to polycarbonate.
PMMA allows infrared light of up to 2800 nm wavelength to pass. IR of longer wavelengths, up to 25,000 nm, are essentially blocked. Special formulations of colored PMMA exist to allow specific IR wavelengths to pass while blocking visible light (for remote control or heat sensor applications, for example).
PMMA can be joined using cyanoacrylate cement (so-called "Superglue"), or by using liquid di- or trichloromethane to dissolve the plastic at the joint which then fuses and sets, forming an almost invisible weld. PMMA can also be easily polished to restore cut edges to full transparency.
To produce 1 kg of PMMA, about 2 kg of petroleum is needed. In the presence of air, PMMA ignites at 460° C and burns completely to form only carbon dioxide and water.
If hydrogen atoms are substituted for the methyl groups (CH3) attached to the Carbon atoms, poly(methyl acrylate) is produced. This soft white rubbery material is softer than PMMA because its long polymer chains are thinner and smoother and can more easily slide past each other.
Structure of methyl methacrylate, the monomer that makes up PMMA
Underwater restaurant Ithaa, five meters below sealevel, is encased in PMMAPMMA or Acrylic is a versatile material and has been used in a wide range of fields and applications.
Impact resistant substitute for glass
PMMA Acrylic glass is commonly used for constructing residential and commercial aquariums.
PMMA is used in the lenses of exterior lights of automobiles.
The spectator protection in ice hockey stadiums is made of PMMA.
Motorcycle helmet visors
Police vehicles for riot control often have the regular glass replaced with acrylic to protect the occupants from thrown objects.
Lucite was used for windows on the Bathyscaphe Trieste which descended to the lowest point on he ocean floor, the Challenger Deep.
Medical Technologies and Implants
PMMA has a good degree of compatibility with human tissue, and can be used for replacement intraocular lenses in the eye when the original lens has been removed in the treatment of cataracts. Hard contact lenses are frequently made of this material. Soft contact lenses are often made of a related polymer, where acrylate monomers containing one or more hydroxyl groups make them hydrophilic.
In orthopaedics, PMMA bone cement is used to affix implants and to remodel lost bone. It is supplied as a powder with liquid methyl methacrylate (MMA). When mixed these yield a dough-like cement that gradually hardens. Surgeons can judge the curing of the PMMA bone cement by pressing their thumb on it. Although PMMA is biologically compatible, MMA is considered to be an irritant and a possible carcinogen. PMMA has also been linked to cardiopulmonary events in the operating room due to hypotension. Bone cement acts like a grout and not so much like a glue in arthroplasty. Although sticky, it primarily fills the spaces between the prosthesis and the bone preventing motion. It has a young's modulus between cancellous bone and cortical bone. Thus it is a load sharing entity in the body not causing bone resorption.
Dentures are often made of PMMA. In cosmetic surgery, tiny PMMA microspheres suspended in some biological fluid are injected under the skin to reduce wrinkles or scars permanently.
Artistic and Aesthetic uses
Acrylic paint essentially consists of PMMA suspended in water; however since PMMA is hydrophobic, a substance with both hydrophobic and hydrophilic groups needs to be added to facilitate the suspension.
Modern furniture makers, especially in the 1960s and 1970s, seeking to give their products a space age esthetic incorporated Lucite and other PMMA products into their designs, especially office chairs. Many other products (for example, guitars) are sometimes made with acrylic glass, giving otherwise ordinary objects a transparent or futuristic look.
Perspex has been used as a surface to paint on, for example by Salvador Dalí.
The material is used to produce laserdiscs, and sometimes also for DVDs, but the more expensive polycarbonate (also used for CDs) has better properties when exposed to moisture.
Used for the "bubble" on the front of submarines.
Artificial fingernails are made of acrylic.
Recently a blacklight-reactive tattoo ink using PMMA microcapsules was developed. The technical name is BIOMETRIX System-1000, and it is marketed under the name "Chameleon Tattoo Ink". This ink is reportedly safe for use, and claims to be Food and Drug Administration approved for use on wildlife that may enter the food supply.
In semiconductor research and industry, PMMA aids as a resist in the electron beam lithography process. A solution consisting of the polymer in a solvent is used to spin coat silicon wafers with a thin film. Patterns on this can be made by an electron beam (using an electron microscope), deep UV light (shorter wavelength than the standard photolithography process), or X-rays. Exposure to these creates chain scission or (cross-linking) within the PMMA, allowing for the selective removal of exposed areas by a chemical developer. PMMA's advantage is that it allows for extremely high resolution (nanoscale) patterns to be made. It is an invaluable tool in nanotechnology.
For the cinema film, see the article Polyester (film).
SEM picture of a bend in a high surface area polyester fiber with a seven-lobed cross sectionPolyester is a category of polymers, or, more specifically condensation polymers, which contain the ester functional group in their main chain. Usually, polyester refers to cloth woven from polyester fiber. Polyester clothing is generally considered to have a "less natural" feeling to it compared to natural fibers. Polyester fibers are often spun together with fibers of cotton, producing a cloth with some of the better properties of each.
Close-up of a polyester shirtAlthough polyesters do exist in nature (e.g., in the cutin of the plant cuticle), polyester generally refers to the large family of synthetic polyesters (plastics) which includes polycarbonate and above all polyethylene terephthalate (PET). PET is one of the most important thermoplastic polyesters.
Polyester is combustible but due to its thermoplastic nature, it tends to shrink away from the flame source and often self-extinguishes.
Polyester is the most widely used manufactured fiber in the United States. Woven fabrics are used for apparel and home furnishings. These include bed sheets, bedspreads, curtains and draperies. Polyester used in knitted fabrics include shirts and blouses. Fiberfill is also used to stuff pillows, comforters and cushion padding. One such fabric is Crimplene.
The first synthetic polyester, glycerine phthalate, was used in the First World War for waterproofing. Natural polyesters have been known since around 1830. The world's largest supplier of unsaturated polyester resin is Reichhold. Reichhold Website
Polyesters are used to make bottles, films, liquid crystal displays, holograms, filters, dielectric film for capacitors, film insulation for wire and insulating tapes.
Liquid crystalline polyesters are among the first industrially used liquid crystalline polymers. In general they have extremely good mechanical properties and are extremely heat resistant. For that reason, they can be used as an abradable seal in jet engines.
Thermosetting polyester resins are commonly used as casting materials, fiberglass laminating resins, and non-metallic auto-body fillers. In such applications, polymerization and cross-linking are initiated through an exothermic reaction involving an organic peroxide, such as methyl ethyl ketone peroxide or benzoyl peroxide.
Polyester is also widely used as a finish on high-quality wooden products like guitars, pianos and vehicle/yacht interiors (Burns Guitars, Rolls Royce and Sunseeker are examples of companies that use polyester on their products). The thixotropic properties of the sprayable form of polyester make it ideal for use on open grain timbers as it can quickly fill the grain and has a high build film thickness per coat. The cured polyester can then be sanded and polished to a high-gloss, durable finish.
Terylene was the first polyester fiber and was produced in England. It was brought to the U.S. in 1951 by DuPont under the trade name Dacron.
Synthesis of polyesters is generally achieved by a polycondensation reaction. See "condensation reactions in polymer chemistry".
In this classical method an alcohol and a carboxylic acid react to form a carboxylic ester. To assemble a polymer, the water formed by the reaction must be continually removed by azeotrope distillation.
See main article on transesterification.
C - OCH3 + OH[Oligomer2]
C - O[Oligomer2] + CH3OH
(ester-terminated oligomer + alcohol-terminated oligomer) (larger oligomer + methanol)
Acylation (HCl method)
The acid begins as an acid chloride, and thus the polycondensation proceeds with emission of hydrochloric acid (HCl) instead of water. This method can be carried out in solution or as an enamel.
In this variant of the HCl method, the carboxylic acid chloride is converted with the trimethyl silyl ether of the alcohol component; trimethyl silyl chloride is produced.
Acetate method (esterification)
Silyl acetate method
Aliphatic polyesters can be assembled from lactones under very mild conditions, catalyzed anionically, cationically or metallorganically.