Effect of molecular weight and temperature on the isothermal crystallization of poly(oxetane)

Abstract

Poly(oxetane) fractions ranging in number-average molecular weights from 7800 to 157000 have been isothermally crystallized in the temperature range from-50 to 19 ~ using dilatometric and calorimetric techniques. In both cases, reproducible isotherms were obtained with an Avrami exponent equal to three. The crystallization rate against crystallization temperature presents a maximum at -30 ~ The level of crystallinity changes with molecular weight and the influence of this parameter on the rate of crystallization is pronounced. The crystallization temperature coefficient was studied using nucleation theory and it was found an slight increase in the basal interfacial free energy for the lowest molecular weight fraction. For the analysis of the temperature coefficient at the higher undercoolings, different approximations for the free energy of fusion and the transport term have been considered. The conclusion of this analysis is that, independently of these approximations, the obtained temperature coefficients are the same.

Liquids That Freeze When Mixed: Cocrystallization and Liquid–Liquid Equilibrium in Polyoxacyclobutane–Water Mixtures

“…The latter was measured by cooling dry POCB650 in a refrigerator to 1–5 °C and then reheating slowly in a water bath. Crystallization studies of water-free POCB of much higher molecular weight − suggest an equilibrium melting temperature of roughly 50 °C, which is the same as the value quoted in the Polymer Handbook . The much lower melting temperature noted here is likely due to the low molecular weight of the material of Figure .…”

“…Incidentally we note that the term “poly­(propylene oxide)” (or glycol) is generally reserved for the polymer with the repeat unit −[CH 2 CH­(CH 3 )­O−] n , which is entirely different from POCB. The earliest research on POCB was initiated in the late 1960s as a part of fundamental studies of semicrystalline polymers. − In most of those and later studies, ,,− POCB was prepared by ring-opening polymerization of oxacyclobutane (also known as oxetane) and had molecular weights ranging from several thousand to over 10 5 g/mol. More recently (∼2007), DuPont commercialized much lower molecular weight grades of POCB, prepared by condensation polymerization of 1,3-propanediol. − Since the 1,3-propanediol was obtained from cereal (corn), this product was given the brand name Cerenol.…”

The relationship between the equilibrium melting temperature and the supermolecular structure of several polyoxetanes and polyethylene oxide

“…The need to heat the polymer melt for various periods or temperatures, to attain the relaxed melt state, to avoid heterogeneous points of nucleation is often mentioned in the literature (4,(18)(19)(20)(21)(22). However, with only a few exceptions (6,19,22), the actual temperature to which the melt is heated is not mentioned. We will show in this paper that the gross morphology that is obtained under any given crystallization conditions is dependent on the temperature to which the melt liquid is heated.…”