Effect of negative pressure on melting behavior of spherulites in thin films of several crystalline polymers

The melting behavior of spherulites in thin films of isotactic polypropylen e, poly(ethylene oxide), poly(methylene oxide), and poly(ethylene adipate) crystallized isothermally at various temperatures has been studied by polar ized light microscopy. The local increase of melting temperature in regions surrounding cavities and multiple boundary points, dependent on the crysta llization temperature, was observed in all studied polymers. In pockets of occluded melt an arising negative pressure lowers an equilibrium melting te mperature; hence, decreases an undercooling, which results in the increase of lamellae thickness and their melting temperature. The elevation of melti ng temperature and the negative pressure buildup depend on the polymer and the crystallization temperature. (C) 1999 John Wiley & Sons, Inc.