LAMELLAR THICKNESS OF POLYETHYLENE SINGLE CRYSTAL ISOTHERMALLY CRYSTALLIZED IN DILUTE SOLUTION

Polyethylene single crystals were formed isothermally from 0.1% solution in tetralin (at 77.2, 84.8, and 89.8°C) and n-hexadecane (106.6°C), and those lamellar thicknesses were investigated as a function of crystallization time. These crystals have revealed no change or, if any, a little change in the lamellar thickness. Even for the crystals formed at considerably high temperature, 106.6°C, at which the segmental motion in a cyrstal begins to become active, the increase in those lamellar thicknesses was of the order of 10 Å. When polyethylene fractions with different molecular weight were crystallized at the same temperature, those lamellar thicknesses have shown nearly the same values. The results observed in this study are in striking contrast to those from isothermal crystallization in bulk, as observed by Hoffman and Weeks. The constancy of the thickness of solution-grown crystals is interpreted as that the longitudinal translation of chains and chain ends in the interior of a crystal, necessary to thickening, will have been restrained on account of a considerably lower crystallization temperature than that in bulk. The lamellar thickness observed is presumed to have nearly equal value to the thickness of the growth nucleus as derived from the kinetic theory by Lauritzen and Hoffman. © 1968 Dr. Dietrich Steinkopff Verlag.