The influence of the equilibrium melting temperature on the supermolecular morphology of several polymers

Abstract

SYNOPSISAt a constant isothermal crystallization temperature ( T,) , the crystalline morphologies of several polymers have been found to be a function of the melt-liquid temperature ( TI). At a constant T, below a critical crystallization temperature T: [about 0.9 Tg ( K ) 1, a transition from a nonspherulitic to a spherulitic morphology occurs when the melt liquid is heated above a melt-liquid transition temperature, ( Tit) [approximately 1.03 T,,, ( K ) 1, where T,,, is the observed melting temperature of the sample. The melt-liquid transition temperature, TI,, which experimentally affects the visible morphology of a semicrystalline polymer, is apparently indistinguishable from the thermodynamic melting temperature, T: , determined by the Hoffman-Weeks procedure. The X-ray powder diffraction patterns of spherulitic and nonspherulitic morphologies were identical, independent of the heating-cooling cycle. This suggests that the transition that occurs at TI, does not affect the arrangement of polymer molecules in the crystallite, but only the manner in which the crystallites are arranged in the supermolecular morphology. The evidence suggests, at least for the polymers studied, that a residual order exists in the melt until the Tt or TI, of the particular polymer is reached.