A linkage moment approach to modeling condensation polymerization with multiple monomers. I. Linear polymers

In recent years, industrial interest in condensation copolymers with contro lled microstructures has been increasing as these systems add an additional dimension to the design and manipulation of product properties without req uiring completely new routes for monomer or polymer synthesis. The techniqu es used to control the compositional microstructure in condensation systems differ greatly from those in vinyl polymerization, as condensation polymer s are continuously broken apart and reformed during the course of the polym erization. Blocky copolymers may be produced in a melt blending process onl y by Limiting the contact time at reaction temperatures because the ultimat e result of the polymerization and interchange reactions is complete random ization of the copolymer with a structure similar to that obtained in vinyl polymerization with all reactivity ratios equal to one. The design of proc esses yielding the desired product microstructure therefore requires a quan titative understanding of the effect of each reaction on the copolymer comp osition. As typical copolymer recipes include multiple monomers with differ ent functionalities, in this paper a general copolycondensation model is pr esented that can accommodate an arbitrary number of monomers of differing r eactivities. In this paper, only monofunctional and bifunctional monomers a re considered; the extension to the case of gelating systems is left for a future paper. The use of this framework and the validity of the approach is demonstrated for an example situation in which a polyarylate is melt blend ed with PET to produce a copolymer whose average sequence length may be con trolled by limiting the extent of reaction. (C) 2000 John Wiley & Sons, Inc .