Complex phase behavior of a weakly interacting binary polymer blend

The complex phase behavior of a weakly interacting binary polymer blend was studied. It was shown that the weakly interacting PS/poly(n-pentylmethacrylate) blend exhibits both a UCST and an LCST. The PS-block-poly(n-pentyl methacrylate) copolymers [PS-b-PnPMA] exhibit closed-loop phase behavior, where the lower disorder-to-order transition (LDOT) and upper-to-disorder transition (UODT) curves from the lower and upper bounds of closed loop. The major difference in the phase behavior of PS/PnPMA blends from that of PS-b-PnPMA copolymers was the lack of evidence of an upper critical solution transition (u-UCST) above an observed LCST in the blend system. The LCST was characterized by a negative volume change on mixing, resulting in enhanced miscibility.