MOLECULAR WEIGHT DEPENDENCE OF CRYSTAL GROWTH RATE AND ITS DEGREE OF SUPERCOOLING EFFECT

Abstract

The molecular weight (MW) dependence of the linear crystal growth rate (G) and the influence of the supercooling on the relationship between MW and G at a given supercooling were studied for poly(ethylene succinate). The spherulite growth rate was measured over a wide range of temperature. It had a bell-shape with a maximum growth rate (G max) that showed a remarkable MW dependence. The MW dependence of G max was mainly a consequence of the MW dependence of G o (pre-exponential factor of the crystal growth rate). The G max increased first with MW up to 3000 and then decreased. The maximum of G max at 3000 was attributed to the transition from extended chain crystallization (ECC) to folded chain crystallization (FCC). The MW dependence of G max was expressed as α was a constant depending on the morphological features of the crystallization. The value of α was nearly unity for ECC below MW of 3000 and α was about −0.5 for FCC above MW of 3000. However, the value of α was strongly dependent on the degree of supercooling when G was plotted against MW at a given supercooling; less supercooling gave a large value of α. The value of α is a function of the adsorption mechanism of polymer molecules on the crystal growth front and its diffusion mechanism. These molecular mechanisms are discussed in this article.