CRYSTALLIZATION OF A COPOLYESTER IN MICROLAYERS AND BLENDS WITH POLYCARBONATE

The crystallization behavior of coextruded microlayered sheets compris ed of 657 alternating layers of polycarbonate (PC) and a miscible copo lyester of mainly 1,4-cyclohexanedimethanol and terephthalic acid (KOD AR) was investigated as a function of annealing time when the KODAR wa s crystallized isothermally from the glass at 195 degrees C. Compariso ns were made with crystallization of KODAR alone, and with crystalliza tion of KODAR from melt blends with PC. The kinetics of crystallizatio n and the morphology of the crystallized KODAR were characterized with differential scanning calorimetry, and by examination of thin section s microtomed from annealed specimens in the polarized light microscope and the transmission electron microscope. The growth rate of small, b irefringent KODAR spherulites was non-linear, and was strongly affecte d by diffusion of PC into the KODAR layers. Diffusion of amorphous PC into the KODAR layers retarded nucleation and spherulite growth and de creased spherulite density. The effect became more pronounced as the K ODAR layer thickness was reduced. Spherulites nucleated randomly throu ghout the KODAR layers in the PC/KODAR 20/80 (w/w) microlayer and grew rapidly to form a continuous layer of impinged spherulites. In contra st, spherulites in the PC/KODAR 40/60 and 60/40 microlayers nucleated and grew along the center of the KODAR layers where the KODAR concentr ation was highest.