Directional Entropy of Chain Folding Detected in Chain Folding Free Energies? Crystal Thickness Transition of isotactic Polybutene-1 Tetragonal Phase

Abstract

Lamellar crystal thickness lc of isotactic polybutene-1 (it-PB1) has been investigated for crystallization in the melt over a wide range of crystallization temperature T from 40 to 90 °C by small angle X-ray scattering experiments and density measurements. The crystal thickness lc demonstrates two linear dependences on inverse supercooling and a transition from one dependence to the other has been observed around T=65 °C. Each of the two dependences obeys the nucleation theory in the high and low supercooling ranges, respectively. Chain folding free energy q determined from the low supercooling range is larger than that determined from the high supercooling range. We discuss possible mechanisms for the transition taking account of entropy of chain folding directions and propose that the difference in the q values could be due to the change in directional entropy of chain folding caused by kinetic roughening.