Phase separation in polydisperse rod-coil block copolymers

The stability limits of the homogeneous state of melts of rod-coil RC, RC2, and CRC polydisperse block copolymers have been investigated in the framework of the weak segregation theory. It was assumed that the number of units in either the rod-like R or the flexible C block is a random variable distributed by the Schulz-Zimm distribution. Inspection of the spinodal curves shows that the copolymer melts with polydisperse rigid blocks are less stable with respect to formation of the nematic state than melts with the monodisperse ones. If flexible C blocks are polydisperse the homogeneous state of a rod-coil melt is less stable against microphase separation than the homogeneous state of monodisperse melt of the same architecture.