Nematic order drives phase separation in polydisperse liquid crystalline polymers

In a polydisperse thermotropic main-chain liquid crystalline polymer, we ob serve lie process of thermally induced nematic-nematic phase separation bet ween short and long polymer chains. We study the dynamical features of this system, in particular the evolution of Schlieren textures Formed by discli nations surrounding areas of relatively uniform director. We analyze the de pendence of domain size xi on temperature and the nematic order parameter, and the evolution of textures with the waiting time at a temperature well b elow the nematic transition T-ni. We End that: before phase separation the coarsening proceeds toward the uniform state, with characteristic size of t he texture increasing as xi similar to t(1/4). When the system is phase-sep arated, the texture in the regions with long chains is frozen at an equilib rium value xi, a reversible function of temperature, while in the short-cha in regions the coarsening accelerates. This behavior is interpreted in term s of a miscibility gap that is proportional to the degree of nematic order, which is different for the different lengths of the nematic polymers.