INTERDIFFUSION IN MICROLAYERED POLYMER COMPOSITES OF POLYCARBONATE AND A COPOLYESTER

The interdiffusion of two miscible polymers, polycarbonate (PC) and a copolyester (KO-DAR), was studied at temperatures from 200 to 230-degr ees-C. The two polymers were coextruded as microlayer composites with up to 3713 alternating layers. The microlayer structure provided a lar ge area of intimate contact between the two polymers with minimal mixi ng. Initially, two glass transition temperatures were observed by DSC that were intermediate between the glass transition temperatures of th e pure components. Upon annealing, the glass transition temperatures s hifted closer together, reflecting the extent to which interdiffusion had occurred. After no more than 2 h of annealing, a single glass tran sition temperature was observed. A model was formulated based on Fick' s law of diffusion that related the mutual diffusion coefficient, D, t o the change in the glass transition temperatures. The model also inco rporated an ''equivalent'' residence time to account for diffusion tha t occurred during the coextrusion process. It was not necessary to con sider the concentration dependence of D to satisfactorily describe the data with this model. For the temperature range from 200 to 230-degre es-C, the value of D varied from 4.0 X 10(-16) to 1.6 X 10(-15) m2 /s. The activation energy of interdiffusion was determined to be 95 kJ/mo l. (C) 1994 John Wiley & Sons, Inc.