Melt Crystallization of isotactic Polybutene-1Trigonal Form: the Effect of Side Chain Entropy on Crystal Growth Kinetics

Abstract

The morphology and crystal growth kinetics of isotactic polybutene-1 (it-PB1) trigonal phase in molten thin films have been studied with transmission electron microscopy, electron diffraction and optical microscopy. The growth rate of trigonal crystals was determined by in situ optical microscopy. It is one hundredth that of it-PB1 tetragonal crystals. The growth rate of trigonal crystals, as well as that of tetragonal crystals, shows the supercooling dependence derived from the nucleation theory. Trigonal crystals grown at 75 and 90.1 °C possessed well facetted morphology, which suggests the existence of flat growth faces required for nucleation theory between 75 and 90.1 °C. This is consistent with the observed temperature dependence of trigonal crystal growth rate in accordance with the nucleation theory. Lateral surface free energy σ of the trigonal phase determined from the observed growth kinetics is about 7 times as large as the value σHoff calculated according to Hoffman’s equation, while that of the tetragonal phase is roughly in agreement with the estimation. The discrepancy between the values of σ and σHoff for the trigonal phase can be attributed to the loss of conformational entropy of the ethyl side chains of it-PB1.