Demixing instability in polymer blends undergoing polycondensation reactions

The stability with respect to demixing of a reacting binary polymer blend i s investigated. In the spirit of earlier work (Read, D. J. Macromolecules 1 998, 31, 899), we combine the random phase approximation for the free energ y with a Markov chain model for the chemistry to obtain the spinodal as a f unction of the relevant degrees of reaction. These are then calculated by a ssuming a simple second-order chemical kinetics. Results are presented, for both linear and branched systems, which illustrate the effects of varying the reaction rates and/or the stiffnesses of the constituent polymer "build ing blocks". Phenomena arise that are not captured by theories assuming equ ality of these parameters.