Graded structure of blend composition in miscible polymer blends comprising polycarbonate and polymethylmethacrylate

A novel method to provide the graded structure in the blend composition of miscible polymer blends was proposed using bisphenol-A polycarbonate (PC) and polymethylmethacrylate (PMMA). We applied a temperature gradient to miscible PC/PMMA blends, in which one component has low molecular weight, beyond their glass transition temperatures. It is found that they exhibit a segregation behavior without showing phase separation. The low-molecular-weight polymer is rich in the high temperature region and vice versa, irrespective of the polymer species. The difference in the blend composition eventually reaches to a constant, at which the migration induced by the applied temperature gradient must compensate with the mass diffusion by composition gradient. Furthermore, the composition gradient in a steady state is found to be proportional to the temperature gradient; i.e., a large temperature gradient results in the pronounced graded structure. In the case of the blends composed of PC and PMMA with low molecular weight, the high temperature side has high surface hardness because of the increase in the PMMA content.