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.