Polyesters interchange reactions

Polymerisation of a diol with a dicarboxybe acid is exemplified by the production of a polyester from ethylene glycol and terephthabc acid either by direct esterification or by a catalysed ester-interchange reaction. The resulting polyester (Terylene) is used for the manufacture of fibres and fabrics, and has high tensile strength and resibency its structure is probably ... 

TPEs associating both rigid and soft polyester blocks have also been described. They cannot be obtained by the melt polyesterification used for polyesterether TPEs, since interchange reactions would yield random—rather than block — copolyesters. The preferred method involves the reaction of OH-terminated aliphatic and aromatic-aliphatic polyesters with chain extenders such as diisocyanates and results in copoly(ester-ester-urethane)s. 

Phenolic compounds are weaker nucleophiles and better leaving groups than aliphatic alcohols. They do not yield polyesters when reacted with carboxylic acids or alkyl carboxy lates. The synthesis of polyesters from diphenols is, therefore, generally carried out through the high-temperature carboxylic acid-aryl acetate or phenyl ester-phenol interchange reactions with efficient removal of reaction by-product (Schemes 2.10 and 2.11, respectively). 

As already discussed (Section 2.2.1.3), interchange reactions are also implicated in the formation of random copolyesters exhibiting the most probable molar mass distribution when polyester blends are melt mixed. They are also involved in the randomization of block copolyesters taking place in the melt upon heating.2,m 211... 

Transesterifications, also termed ester exchange or ester interchange reactions, include hydroxy-ester, carboxy-ester, and ester-ester reactions. Hydroxy-ester reaction is the most important one and is used for many aromatic-aliphatic and wholly aromatic polyester syntheses. Carboxy-ester interchange is restricted to the synthesis of wholly aromatic polyesters while the ester-ester route is rarely used for polyester preparation due to slow kinetics. All these reactions may take place in comparable experimental conditions and can be catalyzed by similar classes of compounds. 

Many random copolyesters and polyester-polycarbonates have also been prepared by ester interchange reactions in the molten state. Thus, poly(ethylene terephthalate-co -isophthalates) can be obtained by simple melt blending of PET and poly(ethylene isophthalate) (PEI) homopolyesters at 270°C. The copolymer changes gradually from a block type at the beginning of reaction to a random-type... 

As is die case for odier polycondensation reactions, internal interchange reactions are possible for ADMET, similar to diat of polyesters and polyamides.16 Interchange reactions involve a catalyst molecule on a polymer chain end reacting widi an internal double bond in another polymer chain. The result is two new polymer chains however, no change in the molecular weight distribution... 

Interchange reactions between two different polymers were observed in the case of polyester or polyamide, but this subject is beyond the scope of the present review. 

The susceptibility of polyesters and polyamides to interchange reactions, such as may occur in the former between a terminal hydroxyl of one molecule and an interunit ester group of another, was discussed in Chapter III. These interchange processes do not decrease the number of molecules, and hence do not affect Mnj but they might permit some molecular species to be formed in preference to others. In other words, they may conceivably bring about an alteration of the molecular size distribution. 

Hydrolysis of Copolyamide-esters (CPAEs) by Lipase (jj,). CPAEs were synthesized by the amide-ester interchange reaction between polyamide and polyester. The length of the polyamide blocks was measured after hydrolysis of ester bonds in CPAE by alkali at 30 C. The infrared spectra after hydrolyzing ester bonds on CPAEs showed that the ester bonds were almost completely removed. The molecular weight distribution of polyamide blocks was examined by GPC (Table II). The following samples were used CPAE-1 (reaction time for synthesis, 1 hr) and CPAE-2 (reaction time, U hr) composed of nylon 6 and PCL at a 50/50 molar ratio, CPAE-3 (reaction time, 1 hr) and CPAE-U (reaction time,... 

Note An interchange reaction that occurs with polyesters is called transesterification. 

If the fractional conversion in an ester interchange reaction is 0.99999, what would be the average degree of polymerization of the polyester produced ... 

It has been established that random interchange reactions occur with polyesters and polyamides at the higli temperatures at which these thermoplastics are normally polymerized and subsequently extruded or molded. Other condensation polymers probably undergo similar shufflings of repeating units under the proper conditions. This implies that the equilibrium constant for condensation reactions like that in reaction (a) of Fig. 5-2 is independent of the sizes of the molecules which are reacting. 

Polyester Fibers Reaction. Ester interchange of ethylene glycol with dimethyl terephthalate is followed by condensation polymerization of the intermediate ... 

A general review of Interchange Reactions Involving Condensation Polymers describes early work on redistribution reactions in the melt blends of polyesters, polyamides, and polyester + polyamide [Kotliar, 1981],... 

Polyesters form a large class of commercially important polymers. A typical polyester is poly(ethylene terephthalate) (PETP), the largest volume synthetic fiber. It is also used as film (mylar) and in bottle applications. We have already discussed in the preceding section one of the routes for the preparation of PETP. The traditional route for the production of commercial PETP is through two successive ester interchange reactions, as shown below ... 

Polyesters are produced commercially by melt polymerization, ester interchanges, and interfacial polymerization. Commercial poly(ethylene terephthalate) is produced traditionally by two successive ester interchange reactions. In the first step, dimethyl terephthalate is heated with ethylene glycol at temperatures near 200°C. This yields an oligomeric dihydroxyethyl terephthalate (x = 1 to 4) and methanol, which is removed. In the second step, the temperature is increased, leading to polymer formation, while ethylene glycol is distilled off. 

PEAs were firstly obtained in 1979 from polyamides and polyesters by temperature-induced amide-ester interchange reactions. Since then, a considerable body of literature has been developed due to the noticeable characteristics and properties of the new polymers. For more detailed information on the synthesis and applications of... 

Block copolyesters also form in reactions between hydroxy and acid chloride-terminated prepolymers. This can take place in the melt or in solution in such solvents as chlorobenzene or o-dichlorobenzene. For relatively inactive acid chlorides, like terephthaloyl chloride, high reaction temperatures are required. Phosgene also reacts with hydroxy-terminated polyesters to form block copolymers. The reactions must be carried out in an inert solvent. Block copolyethers also form readily by ester interchange reactions with low molecular weight diesters ... 

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