Stable Critical Gels of a Copolymer of Ethene and 1-Butene Achieved by Partial Melting and Recrystallization

Abstract

The transition from solid to liquid during the melting of a semicrystalline polymer can be viewed as reverse gelation since the physical gel point (state of liquid-to-solid transition) is approached from the solid side. In this study we explore routes of stopping the melting process at the gel point and stabilizing the semicrystalline structure at sufficiently low crystallinity. Such material at the gel point is called a “critical gel”. By approaching the gel point from the solid state, we are indeed able to form a stable critical gel. Under the applied conditions, slowly heating (0.2 K/min) from room temperature to the annealing temperature, the stable critical gel was found at 71 °C. One purpose of making stable critical gels is to measure its structure and properties. The critical gel was found to be relatively soft, having a surprisingly high relaxation exponent. The crystallinity at the gel point is below 1 wt %. Crystalline regions whose nature is mostly unknown achieve connectivity between molecules.