THE CRYSTALLIZATION KINETICS OF LOW-MOLECULAR-WEIGHT POLYETHYLENE FRACTIONS

Overall crystallization rates of low-molecular-weight fractions of linear polyethylene have been measured. The molecular weights range from MN = 2900 to MN = 11 400 and quantitative data were obtained in the temperature interval of 110 to 127°C, depending on the molecular weight. Crystallization kinetics obey nucleation theory appropriate to chains of finite length. Definite continuity is found between the kinetics of fractions with molecular weights greater than 8000 and high-molecular-weight fractions. The three lowest molecular-weight fractions appear to display some unique kinetic features. All the fractions display three distinct regimes and the transition temperature between regimes can be identified with characteristics in nucleation rates and do not correspond to an integral change in crystallite thickness. © 1990.