Influence of Chemical Structures on Isodimorphic Behavior of Three Different Copolycarbonate Random Copolymer Series

Abstract

Three series of aliphatic random copolycarbonates, poly(heptane-co-dodecane carbonate) P7C-P12C, poly(butane-co-dodecane carbonate) P4C-P12C and poly(butane-co-heptane carbonate) P4C-P7C, were synthesized by two-step polycondensation process. The organocatalyst 4-(dimethylamino) pyridine (DMAP) was used for the first time to prepare copolycarbonates, as an alternative to metal catalysts, to avoid the toxicity of the remaining catalysts impurities that are difficult to remove after synthesis. Differential scanning calorimeter studies demonstrated the isodimorphic character of the copolycarbonates showing pseudo-eutectic points and the crystallization in a wide composition range. Wide angle X-ray scattering (WAXS) results displayed changes in crystallographic plane spacings possibly due to the isodimorphic behavior of the systems. Two double crystalline copolymers were obtained, i.e., 85/15 P4C-P12C and 80/20 P7C-P12C, as they correspond to pseudo-eutectic compositions. Remarkably, for the 80/20 P7C-P12C copolycarbonate, we found a novel behavior. This copolymer exhibits both coincident crystallization and coincident melting during non-isothermal DSC runs. However, WAXS revealed that the material is double crystalline as it contains crystals from P7C-rich and P12C-rich phases. This is the first example of a double crystalline polymeric material that exhibits a single crystallization and a single melting peak, in spite of being double crystalline. Comparing the results obtained for the 3 series of copolycarbonates, we can conclude that it is easier to incorporate a shorter repeating unit chain segment in a crystal formed by a larger repeating unit chain segment.