Polyethylene terephthalate, unit

Those polymers which are the condensation product of two different monomers are named by applying the preceding rules to the repeat unit. For example, the polyester formed by the condensation of ethylene glycol and terephthalic acid is called poly(oxyethylene oxyterphthaloyl) according to the lUPAC system, as well as poly (ethylene terephthalate) or polyethylene terephthalate. 

Perhaps the most important polyester is polyethylene terephthalate), commonly known as PET (or PETE 1 on plastic beverage bottles). The annual production of PET in the United States is of the order of 108 kg (105 metric tons). Much of this is converted into fabric (trade name, Dacron) or magnetically coated film (Mylar). 

Once a consumer has purchased a material made of a polymer, the likelihood of it being recycled is dramatically reduced. In the United States there are three resins that are commonly recycled polyethylene, polypropylene, and polyethylene terephthalate, SPI (The Society of the Plastics Industry) recycling codes, found on the bottom of food containers, provide the consumer with information as to the recyclability of the material. Table 17,1 lists these codes. 

In addition to the desired polymerization reaction, the dialcohol reactants can participate in deleterious side reactions. Ethylene glycol, used in the manufacture of polyethylene terephthalate, can react with itself to form a dialcohol ether and water as shown in Fig. 24.4a). This dialcohol ether can incorporate into the growing polymer chain because it contains terminal alcohol units. Unfortunately, this incorporation lowers the crystallinity of the polyester on cooling which alters the polymer s physical properties. 1,4 butanediol, the dialcohol used to manufacture polybutylene terephthalate, can form tetrahydrofuran and water as shown in Fig. 24.4b). Both the tetrahydrofuran and water can be easily removed from the melt but this reaction reduces the efficiency of the process since reactants are lost. 

Polyethylene terephthalate crystallizes very slowly into only one stable crystalline form, containing monoclinic unit cells. To maximize its physical strength, high crystallinities must... 

Poly (ethylene Terephthalate). Polyethylene terephthalate) is prepared by the reaction of either terephthalic acid or dimethyl terephthalate with ethylene glycol, and its repeating unit has the general structure. 

For most step polymerizations, for example, in the synthesis of polyl hexamethylene adipa-mide) or polyethylene terephthalate), two reactants or monomers are used in the process, and the polymer obtained contains two different kinds of structures in the chain. This is not the case for chain polymerizations, where only one monomer need be used to produce a polymer. However, chain polymerizations can be carried out with mixtures of two monomers to form polymeric products wiht two different structures in the polymer chain. This type of chain polymerization process in which two monomers are simultaneously polymerized is termed a copolymerization, and the product is a copolymer. It is important to stress that the copolymer is not an alloy of two homopolymers hut contains units of both monomers incorporated into each copolymer molecule. The process can be depicted as... 

Chemically, Dacron and Mylar are polymers made from a ring structure called dimethyl terephthalate and ethylene glycol (HO-CH2CH2-OH). The polymer unit is called polyethylene terephthalate, or PET. Dacron fiber is used in tires and fabrics, and is even used to repair blood vessels. Mylar is used in magnetic recording tape. In the 1960s, it was used in huge balloons that were sent into orbit around Earth. Plastic soda containers are made of PET. 

In fibres of some polymers, made under certain conditions, the crystalline regions are found to be tilted with respect to the fibre axis in a well-defined crystallographic direction. This is a very valuable feature, because the diffraction patterns of specimens in which this type of orientation occurs are of precisely the same form as tilted crystal diffraction patterns of single crystals rotated round a direction inclined to a principal axis. The unit cell cannot be obtained directly, for 90° oscillation tilted crystal photographs are required for direct interpretation, but unit cells obtained by trial can be checked by the displacements of diffraction spots from the layer lines this is a severe check, and consistent displacements would leave no doubt of the correctness of a unit cell. This procedure played an effective part in the determination of the unit cell of polyethylene terephthalate (Daubeny, Bunn, and Brown, 1954). 

In the case of copolymers a calorimetric investigation by Dole and Wunderlich (1959) of the copolyester, polyethylene terephthalate and sebacate) at the 80/20. (80 moles of terephthalate units to 20 of sebacate)... 

Seven families of thermoplastics exceed a billion pounds per year in the United States polyethylenes, polypropylene, PVC, polystyrene and its copolymers, polyethylene terephthalate, acrylonitrile-butadiene-styrene (ABS) and nylon (Table 15.2). 

PET, polyethylene terephthalate), the primary constituent of a commonly used type of plastic, is composed of the rigid planar terephthalic acid units (HOCO-C6H4-COOH), which are esterified with the flexible ethylene glycol links (HOCH2-CH2OH) ... 

SSP [Solid State Polymerization] Also called UOP Sinco SSP. A process for making articles from PET (polyethylene terephthalate) and related polymers. The key step is controlled crystallization of the polymer under optimum conditions. Developed jointly by UOP (United States) and Sinco (Italy) and widely adopted since 1986. 

UnPET [United Resource Recovery PolyEthylene Terephthalate] A process for recycling waste PET (polyethylene terephthalate). The PET is first hydrolyzed by hot aqueous alkali, and the product then undergoes five complex processes. The only products leaving the process are terephthalic acid, ethylene glycol, carbon dioxide, and water. Developed from 1996 by the United Resource Recovery Corporation, Spartanburg, SC, and operated on a large scale in Switzerland, Germany, and the United States. 

Figure 5. Decomposed ESCA carbon is spectra of Beulah lignite (—) and polyethylene terephthalate (—). Plot is of a number of electrons per energy in arbitrary units vs. binding energy in electron volts. The lignite spectrum has been corrected for sample charging (11).

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