Crystallization of polyethylenes at very high supercooling

The crystallization behavior of a series 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 WAXD 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.; The crystallization and morphology of four LLDPE samples produced using metallocene catalysts through the copolymerization of ethylene and octene has been studied. The second part of the study is primarily concerned with the growth kinetics obtained through experimentally determined growth rates at different crystallization temperatures of low and high molecular weight samples. Using experimentally determined equilibrium melting points secondary nucleation behavior is studied in detail. Three Regimes are seen for a molecular weight 101,000 with no branching and at 60,000 with branching at 4 octenes per 1000 carbons. Two Regimes have been obtained for a sample of similar molecular weight but with branching at 17 octenes per 1000 carbons. Lamellar thickness data in the rapid cooling region correlate well with previous studies of the equilibrium melting temperature of the linear polyethylene. Andrews plot data shows a three-stem nucleus in Regime III.