Monte-Carlo Modeling of Exchange-Reactions in Polyesters - Dependence Of Copolymer Composition On The Exchange Mechanism

Abstract: Two models were developed which describe the synthesis of an A/B copolyester via reactive blending of a mixture of homopolyester A and homopolyester B. The models take into account two different exchange mechanisms: the first one describes inner-group ester-ester exchange, and the second describes the process in which an active terminal group attacks an ester group. The two models were incorporated in a computer program, MOSES, which simulates the exchange reaction using the Monte Carlo approach. The models yield different values for the composition of the copolymer formed: the first one predicts that the copolymer composition is always identical to the sample composition, whereas the second one predicts that deviations can occur in the initial stages of the process. This result can be used to discriminate between the two exchange mechanisms. The predictions of the two models are compared with recent experimental mass spectral data concerning a poly(ethylene adipate-co-ethylene terephthalate) copolyester. Comparison with experiment favors the active end group mechanism. The dependence of copolymer composition on reaction conditions was investigated using the MOSES program. From the overall set of concentration values calculated, a simple analytical formula was found (eq 9) which allows computation of the copolymer composition from the knowledge of the reaction conditions.