Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. II. Kinetic study

A kinetic study of crystallization of fractions of poly(ethylene oxide)s between 3500 and 5,000,000 MW and their mixtures from the melt by differential scanning calorimetry and optical microscopy is reported. For the fractions the crystal growth rate is inversely dependent on the logarithmic molecular weight. Binary mixtures of widely different molecular weights show mixed‐crystal formation at low crystallization temperature described by a single Avrami equation with exponent 3. At higher temperature, increasing segregation takes place despite higher deposition probabilities of the low molecular weight. Two consecutive Avrami equations describe the crystallization. Before the equilibrium melting temperature of the low molecular weight component is reached, complete segregation occurs. This segregation is possible up to at least 20,000 MW. Classical crystallization theory is unable to describe the process. Molecular nucleation seems a viable alternative for the description of crystallization of both fractions and mixtures. Reversibility of crystallization is on a one‐molecule scale and reaches thermodynamic reversibility as the molecular length approaches monomer size.