POLY(EPSILON-CAPRALACTONE) POLY(ETHYLENE OXIDE) DIBLOCK COPOLYMER .2.NONISOTHERMAL CRYSTALLIZATION AND MELTING BEHAVIOR/

The nonisothermal crystallization behavior and melting process of the poly(epsilon-caprolactone) (PCL)/poly(ethylene oxide) (PEG) diblock co polymer in which the weight fraction of the PCL block is 0.80 has been studied by using differential scanning calorimetry (DSC). Only the PC L block is crystallizable, the PEO block with 0.20 weight fraction can not crystallize. The kinetics of the PCL/PEO diblock copolymer under n onisothermal crystallization conditions has been analyzed by Ozawa's e quation. The experimental data shows no agreement with Ozawa's theoret ical predictions in the whole crystallization process, especially in t he later stage. A parameter, kinetic crystallinity, is used to charact erize the crystallizability of the PCL/PEO diblock copolymer. The amor phous and microphase separating PEO block has a great influence on the crystallization of the PCL block. It bonds chemically with the PCL bl ock, reduces crystallization entropy, and provides nucleating sites fo r the PCL block crystallization. The existence of the PEO block leads to the occurrence of the two melting peaks of the PCL/PEO diblock copo lymer during melting process after nonisothermal crystallization. The comparison of nonisothermal crystallization of the PCL/PEO diblock cop olymer, PCL/PEO blend, and PCL and PEO homopolymers has been made. It showed a lower crystallinity of the PCL/PEO diblock copolymer than tha t of others and a faster crystallization rate of the PCL/PEO diblock c opolymer than that of the PCL homopolymer, but a slower crystallizatio n rate than that of the PCL/PEO blend. (C) 1997 John Wiley & Sons, Inc .