Crystallization of polyethylenes at very high supercooling

The crystallization behavior of a senes of ethylene-octene copolymers synthesized using metallocene catalysts has been studied using the Ding-Spruiell method of rapid cooling. In conventional crystallization experiments it was found, as expected, that the spherulite growth rates varied with octene content and molecular weight. When studied at rapid cooling rates the polymers generate their own pseudo-isothermal crystallization temperatures, in agreement with Ding - Spruiell's studies on other systems, however, at the lowest temperatures of crystallization, the spherulite growth rates of all the copolymers studied merge. The W AXD results indicate at the faster crystallization rates that the size of the unit cell unit decreases with decreasing crystallization temperature. A resulting increase in the surface free energy plays a role in the behavior of the copolymers such that spherulitic growth rates of copolymers begin to surpass that of the linear polyethylene at very high supercooling. This is a change in the behavior of the copolymers that should be of considerable relevance to polymer processing conditions. Spinodal transformation could play of role in the leveling off of growth rates at high supercooling.