Microphase separation in correlated random copolymers

In this paper we present the results of a calculation of the phase diagram of a highly polydisperse multiblock copolymer in the weak segregation limit. The theory for polydisperse systems developed by Erukhimovich and Dobrynin [Erukhimovich, I.; Dobrynin, A.V. Macromol.Symp, 81, 253 (1994)] has been used. The model of the copolymer has the following characteristics: the blocklengths, as well as the molecule lengths are highly polydisperse (M(w)/M(n) = 2). The average number of blocks per molecule is very large and the effects of the finiteness of the blocklengths (the fluctuation corrections) are ignored. The resulting phase diagram shows some remarkable differences with the phase diagram of a regular monodisperse multiblock. Known differences are e.g. the order of the transition from the homogeneous state, and the variation of the period of the microstructure with the chi-parameter. Ln addition, we found a peculiar feature at the critical point: the phase boundaries have discontinuous derivatives

ENTHALPY RELAXATIONS AND CONCENTRATION FLUCTUATIONS IN BLENDS OF POLYSTYRENE AND POLY(OXY-2,6-DIMETHYL-1,4-PHENYLENE)

A series of enthalpy relaxation measurements were carried out for the pure polymers polystyrene (PS) and poly(oxy-2,6-dimethyl-1,4-phenylene) (PPE) and for homogeneous blends thereof. The data were analyzed using Moynihan's four-parameter approach.4 For the pure components the best fit parameter values for the simple cooling/heating experiments differ somewhat from those for the annealing experiments at least partly due to thermal lag. The amount of enthalpy relaxation during annealing of the blends turned out to be considerably lower than for the corresponding homopolymers. Moreover, the annealing experiments on the blends could not be fit satisfactorily with the Moynihan model. The first observation agrees with a similar result found by Cowie and Ferguson17 for blends of PS and poly(vinyl methyl ether). Since this effect is not present for a number of polymer blends involving polymers with comparable glass transition temperatures, it seems to be related to the large difference in glass transition temperatures of the blend components. The presence of concentration fluctuations, with a corresponding range of T(g) values, is the most obvious explanation for both observations