Polyethylene terephthalate polymerization reaction

As in chemical reactions of small molecules, condensation polymerizations also have an equilibrium. In fact, in several cases (e.g., polyethylene terephthalate polymerization), equilibrium is attained at very low values of n , and high vacuum must be applied to drive the reaction in the forward direction to get polymer of high enough molecular weight to be of commercial interest... 

Condensation polymerization differs from addition polymerization in that the polymer is formed by reaction of monomers, each step in the process resulting in the elimination of some easily removed molecule (often water). E.g. the polyester polyethylene terephthalate (Terylene) is formed by the condensation polymerization (polycondensation) of ethylene glycol with terephthalic acid ... 

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. 

Wu, D., Chen, F. and Li, R., Reaction kinetics and simulations for solid-state polymerization of polyethylene terephthalate), Macromolecules, 30, 6737-6742 (1997). 

The most important polyester is polyethylene terephthalate (PET), which has mariy uses, from fabrics to milk bottles. The polymerization reaction between ethylene glycol (EG) and terephthahc acid (TPA),... 

Polymerization of esters to produce polyesters is an important commercial process. Polyethylene terephthalate or PET is one of the most common plastics used in food containers (Table 15.4). This ester is formed by the reaction of ethylene glycol and terephthalic acid (Figure 15.17). PET and other polyesters consist of esters linked together. Notice that both terephthalic acid and ethylene glycol have two carboxyls and two hydroxyls, respectively. When a polyester such as PET is formed, a monomer con-... 

The largest commercial use of ethylene glycol is its reaction with dicarboxylic acids to form linear polyesters. Polyethylene terephthalate) [25038-59-9] (PET) is produced by esterification of terephthalic acid [100-21 -0] (1) to form bishydroxyethyl terephthalate [959-26-2] (BHET) (2). BHET polymerizes in a transesterification reaction catalyzed by antimony oxide to form PET (3). 

Condensation polymerizations are equilibrium reactions, which means they eventually stop reacting when small molecular weight reaction products like water are no longer removed from the system. These characteristics of the condensation polymerization reaction also have an effect on the chemical properties of such plastics. In the presence of water, particularly at high temperatures, polyethylene terephthalate begins to hydrolyze and low molecular weight oligomers are produced which can be transferred into a food in contact with the plastic. 

Liquefaction of untreated wood can also be achieved at a lower temperature of 150°C and at atmospheric pressure in the presence of a catalyst [12]. Phenolsulfonic acid, sulfuric acid, hydrochloric acid, and phosphoric acid were used as catalysts. In this acid catalyst method, phenols and polyhydric alcohols can also be used for the coexisting organic solvents. Phenol, cresol, bisphenol A and F, and so forth are successfully adoptable as the phenols. Polyethylene glycols, polyether polyols (epoxide additionally reacted polyether polyol, polyethylene terephthalate polyol) have been found to liquify wood resulting in polyol solutions [13]. Liquefaction of wood in the presence of -caprolactone, glycerin, and sulfuric acid has also been accomplished. It was confirmed in this case that liquefaction and polymerization, the latter of which produces polycaprolactone, take place in the reaction system at the same time [14]. Besides the wood material, it has become apparent that trunk and coconut parts of palm, barks, bagasse, coffee bean wastes, and used OA papers can also be liquified [15]. 

Polyesters are formed by step-growth polymerization using nucleophilic acyl substitution reactions, as we learned in Section 22.16B. For example, the reaction of terephthalic acid and ethylene glycol forms polyethylene terephthalate (PET), a polymer commonly used in plastic soda bottles. Polyethylene terephthalate is also sold as Dacron, a lightweight and durable material used in textile manufacturing. 

Unbreakable children s toys are often made of polyethylene, which is synthesized by polymerizing ethene under pressure. Two monomers react to form polyethylene terephthalate (PET), a versatile plastic that is used to make bottles and recording tape. When made into fiber, it is called Dacron. Polyethylene and PET, examples of polymers made by two types of reactions, are shown in Table 23-3. 

The second of the two basic polymerization processes that results in linear chain molecules is the condensation reaction where, e.g., in the case of formation of the polyester, polyethylene terephthalate (PET), as shown in Fig. 2.3, two separate monomers, ethylene glycol and terephthalic acid, react and give off a reaction product, H2O, in a systematic process that results in a chain polymer. 

A special form of condensation polymerization occurs when the monomer can react with itself Conceptually, the monomer has the form AMB. The initial stoichiometry is perfect so there is no inherent limitation on molecular weight. Typically, however, there is an equilibrium limitation caused by the condensation by-product. Self-condensing polymerizations can be regarded as a special case of binary polycondensations, as discussed above, that start with the dimer, AMNB. This view is a bit misleading with respect to the actual chemistry. The final reaction step in the manufacture of polyethylene terephthalate is... 

Hydrolysis reactions have been widely reported in NCW for low-molecular-weight molecules as well as for polymeric materials. Mandoki reported a process for depoly-merizing condensation polymers using NCW without addition of bases or acids. More particularly, polyethylene terephthalate, polybutene terephthalate, nylon 6, and nylon 66 were hydrolytically depolymerized (Fig. 9.25). 

Instead of the addition pol)nnerization described above, some polymers are formed by a chemical reaction between two monomers that produces the repeating units together with a byproduct. This process is called condensation or step reaction polymerization. An example would be the reaction between dimethyl terephthalate and ethylene glycol to produce polyethylene terephthalate (PET) and methyl alcohol as a byproduct. The nylons and polycarbonates are linear chain pol)nners that also pol)nnerize by the condensation process. 

In bulk polymerization, the only components of the formulation are monomers and the catalyst or initiator. When the polymer is soluble in the monomer, the reaction mixture remains homogeneous for the whole process. Examples of homogeneous bulk polymerization are the production of low-density polyethylene (LDPE), general purpose polystyrene and poly(methyl methacrylate) produced by free-radical polymerization, and the manufacture of many polymers produced by step-growth polymerization including poly(ethylene terephthalate), polycarbonate and nylons. In some cases (e.g., in the production of HIPS and acrylonitrile-butadiene-styrene (ABS) resins), the reaction mixture contains a preformed... 

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