Concurrent crystallization and interdiffusion in microlayers of polycarbonate and a copolyester

Abstract

AbstractConcurrent crystallization and interdiffusion of two miscible polymers, polycarbonate (PC) and a copolyester (KODAR), was studied in microlayers 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 microlayers were annealed above the glass transition of PC were determined by DSC and DMTA. When the annealing temperature was 200°C or higher, interdiffusion was much faster than crystallization and the glass transitions gradually shifted closer together until they merged into a single transition. An analysis based on Fick's law of diffusion described the relationship between the glass transition temperatures and the annealing time. At 195°C, the rates of interdiffusion and crystallization were comparable. Annealing at this temperature resulted in more complex changes in the glass transitions, including the persistence of two transitions after long annealing times. This behavior was understood by considering an interlamellar amorphous phase that was trapped in the spherulites and not available for interdiffusion. Models were developed from the spherulite morphology observed in the optical microscope. Two cases were considered: a continuous layer of impinged spherulites in the PC/KODAR 20/80 (w/w) composition, and isolated spherulites aligned with the center of the KODAR layer in PC/KODAR 40/60 and 60/40. These models satisfactorily reproduced the principal features of concurrent crystallization and interdiffusion.