POLY(EPSILON-CAPROLACTONE) POLY(ETHYLENE OXIDE) DIBLOCK COPOLYMER .1.ISOTHERMAL CRYSTALLIZATION AND MELTING BEHAVIOR/

The isothermal crystallization and melting behavior of the poly(epsilo n-caprolactone) (PCL)/poly(ethylene oxide)(PEO) diblock copolymer has been studied by WAXD, SAXS, and DSC methods. Only the PCL block is cry stallizable; the PEO block of weight fraction 20% cannot crystallize, although its corresponding homopolymer has strong crystallizability. T he long period, amorphous layer, and crystalline lamella of the PCL/PE O block copolymer all increase with the rise in the crystallization te mperature, and the thickness of the amorphous layer is much larger tha n that of crystalline lamella due to the existence of the PEO block in the amorphous region. The isothermal crystallization of the PCL/PEO b lock copolymer is investigated by using the theory of Turnbull and Fis cher. It is found that the amorphous PEO block has a great influence o n the nucleation of PCL block crystallization, and the extent of this influence depends on crystallization conditions, especially temperatur e. The outstanding characteristics are the phenomenon of the double me lting peaks in the melting process of the PCL/PEO block copolymer afte r isothermal crystallization at different temperatures and the transfo rmation of melting peaks from double peaks to a single peak with varia tions in the crystallization condition. They are related mainly to the existence of the PEO block bonding chemically with the PCL block. In summing up results of investigations into the crystallization and melt ing behavior of the PCL/PEO block copolymer, it is interesting to noti ce that when the PCL/PEO block copolymer crystallizes at three differe nt crystallization temperatures, i.e., below 0 degrees C, between 0 an d 35 degrees C, and above 35 degrees C, the variation of peak melting temperature is similar to that of overall crystallization rates in the process of isothermal crystallization. The results can be elucidated by the effect of the PEO block on the crystallization of the PCL block , especially its nucleation. (C) 1996 John Wiley & Sons, Inc.