The Effects of Intramolecular Interactions of Random Copolymers on the Phase Behavior of Polymer Mixtures

To explore the effects of intramolecular interactions within the copolymer on the phase separation behavior of polymer blends, copolymers having two different types of intramolecular interactions, i.e., intramolecular repulsion and intramolecular attraction were prepared . In this study, poly(styrene-co-methylmethacrylate) (P(S-MMA)) having intramolecular repulsion caused by positive interaction between styrene and MMA and poly(styrene-co-ethyl-methacrylate) (P(S-EMA)) and poly(styrene-co-cyclohexylmethacrylate) (P(S-CHMA)) having intramolecular attraction caused by negative interaction between styrene and methacrylate were blended with tetramethyl poly-carbonate (TMPC). The phase behavior of blends was examined as a function of copolymer composition and blend composition. TMPC formed miscible blends with styrenic copolymers containing less than certain amount of methacrylate. The phase separation temperature of TMPC blends with copolymer such as P(S-MMA) and P(S-EMA), first increases with methacrylate content, goes through a maximum and then decreases just prior to the limiting content of methacrylate for miscibility, while that of TMPC blends with P(S-CHMA) always decreases. The calculated interaction energy for TMPC-P(S-EMA) pair is negative and monotonically increases with EMA content of the copolymer. Such behavior contradicted the general notion that systems with more favorable energetic interactions have higher LCST, The detailed inspection of the lattice-fluid theory related to the phase behavior was performed to explain such behavior.