Crystallization Kinetics of an Ethylene Oxide-Propylene Oxide Triblock Copolymer (sym-EPE) in Dilute Solution from the Field-Free Decay of the Electric Birefringence

Abstract

The field-free decay of the electric birefringence (Kerr effect) was used to determine the growth of single crystals in ethylbenzene containing 2 mg/mL of a PEO-PPO-PEO triblock copolymer, where PEO and PPO denote poly(ethylene oxide) and atactic poly(propylene oxide), respectively. The linear size of the crystals was found to increase in proportion to the square root of time over a substantial portion of the crystallization period at temperatures from 16.5 to 24.4 °C; the solutions were self-seeded at temperatures from 30.1 to 34.0 °C. When the crystallization temperature was increased 6.5 °C, the half-time for crystallization increased 30-fold. The unusual dependence of the size of growing crystals on time has been reported previously only by Kovacs and Manson for the crystallization of a diblock copolymer of atactic polystyrene and PEO from dilute solutions. From optical micrographs of the crystals in three suspensions, we found that the size distribution of the crystals is narrow and that the average size agrees closely (≤2%) with that obtained from the field-free decay of the electric birefringence. Data from SAXS and DSC measurements indicate that the crystal thickness increases significantly with the crystallization temperature and that 15-23% of the units in the PEO segments reside in the amorphous layers on the crystals. © 1982, American Chemical Society. All rights reserved.