Integral equation theory of randomly coupled multiblock copolymer melts: effect of block size on the phase behavior

The phase behavior of randomly coupled multiblock copolymer melts is studied using the polymer reference interaction site model integral equation theory. The molecules are modeled as flexible chains with random sequences of two types of blocks, each of which consists of the same number (R) of monomer beads. In the random copolymer (R=1) limit the theory predicts macrophase separation as the temperature is decreased for all values of the monomer correlation length lambda. For R>2, however, the theory predicts a microphase separation for values of lambda less than some critical value which increases as the block size increases.