Condensation polymers interchange reactions

Similar interchange processes may occur in other condensation polymers under suitable conditions. There is ample evidence in the literature on polyamides, and on monomeric amides as well, for the occurrence of the amine-amide interchange reaction (II)... 

The common condensation polymers and the reactions by which they are formed are shown in Table 1-1. It should be noted from Table 1-1 that for many of the condensation polymers there are different combinations of reactants that can be employed for their synthesis. Thus polyamides can be synthesized by the reactions of diamines with diacids or diacyl chlorides and by the self-condensation of amino acids. Similarly, polyesters can be synthesized from diols by esterification with diacids or ester interchange with diesters. 

A variety of polyester-condensation polymers are made commercially. Ester interchange (Section 18-7 A) appears to be the most useful reaction for preparation of linear polymers ... 

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. 

The condensation polymer made by reacting ethylene glycol with 1,4-benzene dicarboxylic acid (terephthalic acid) produces a polymer that is almost exclusively converted into the fiber Dacron. The polymerization is run as an ester interchange reaction using the methyl ester of terephthalic acid ... 

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 were historically the first synthetic condensation polymers studied by Carothers in his pioneering work in the early 1930s. Commercial polyesters [30] were manufactured by polycondensation reactions, the methods commonly used being melt polymerization of diacid and diol, ester interchange of diester and diol, and interfacial polymerization (Schotten-Baumann reaction) of diacid chloride and diol. In a polycondensation reaction a by-product is generated which has to be removed as the reaction progresses. 

Kotliar, A.M., Block Sequence distribution and homopolymer content for condensation polymers undergoing interchange reactions, /. Polym. Set., Polym. Chem. Ed, 13, 973 (1975). 

The mechanisms required for the reaction mixture are (i) a graft or block copolymer formed by the chemical reaction between the chemical reactivities in the polymer chains, which can be initiated by the addition of an initiator to the mixing process (ii) the formation of a block copolymer by an interchange reaction between the molecular chains of each type of the condensation-type... 

Interchange reactions are common in polycondensation chemistry, and occur when the functional groups in the polymer backbone continue to be active toward the condensation reaction. These reactions do not affect the average molecular weight of the polymer and, in that sense, are degenerate. In the case of ADMET, the internal carbon-carbon double bonds of the polymer are still metathesis-active, and can undergo reaction with either the metal methylidene or a polymeric metal alkylidene. 

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