Solvent effects on the miscibility of poly(methyl methacrylate)/poly(bisphenol A carbonate) blends

Blends of atactic or syndiotactic poly(methyl methacrylate) (designated as aPMMA or sPMMA) and poly(bisphenol A carbonate) (PC) were prepared from solution casting. Tetrahydrofuran (THF) and chloroform were used as solvent. Experimental results indicated that the as-cast blends from THF were quite different from the chloroform-cast ones. After film preparation, THF-cast blends did not show any visible phase separation. However, chloroform-cast blends formed a phase-separated structure. The as-cast PC from either solvent was not completely amorphous, and had a melting point at 239-242 degreesC, indicating a certain degree of crystallinity. In contrast, the quenched samples of aPMMA/PC blends prepared from the two solvents behaved virtually the same. They both showed aPMMA dissolves better in PC, but PC solubility in aPMMA is very little. Using sPMMA instead of aPMMA to blend with PC, different results were obtained. The quenched sPMMA/PC blends cast from THF showed only one T-g. However, immiscibility (i.e., two T(g)s) was found in the same blend system when cast from chloroform. THF was believed to cause the observation of single T-g due to the following kinetic reason. sPMMA and PC were still trapped together even after THF removal in a homogeneous, but nonequilibrium state below the glass transition. Therefore, the quenched sPMMA/PC blends were not truly thermodynamically miscible. From the results of aPMMA or sPMMA with PC, increasing syndiotacticity seemed to improve the miscibility between PMMA and PC. (C) 2001 John Wiley & Sons, Inc.