CONCURRENT CRYSTALLIZATION AND INTERDIFFUSION IN MICROLAYERS OF POLYCARBONATE AND A COPOLYESTER

Concurrent crystallization and interdiffusion of two miscible polymers , polycarbonate (PC) and a copolyester (KODAR), was studied in microla yers with 657 alternating layers. Minimal mixing of the two components during processing was indicated by separate glass transitions of the PC and KODAR layers. Changes in the glass transitions after the microl ayers were annealed above the glass transition of PC were determined b y DSC and DMTA. When the annealing temperature was 200 degrees C or hi gher, interdiffusion was much faster than crystallization and the glas s transitions gradually shifted closer together until they merged into a single transition. An analysis based on Fick's law of diffusion des cribed the relationship between the glass transition temperatures and the annealing time. At 195 degrees C, the rates of interdiffusion and crystallization were comparable. Annealing at this temperature resulte d in more complex changes in the glass transitions, including the pers istence of two transitions after long annealing times. This behavior w as understood by considering an interlamellar amorphous phase that was trapped in the spherulites and not available for interdiffusion. Mode ls were developed from the spherulite morphology observed in the optic al microscope. Two cases were considered: a continuous layer of imping ed spherulites in the PC/KODAR 20/80 (w/w) composition, and isolated s pherulites aligned with the center of the KODAR layer in PC/KODAR 40/6 0 and 60/40. These models satisfactorily reproduced the principal feat ures of concurrent crystallization and interdiffusion.