Structure of oligourethanes: 6. Fine structure of melt crystallized oligourethanes

Abstract

The structure and the structure change of the melt crystallized oligourethanes, CH 3CO ▪(CH 2) 5NHCO ▪ nOCH 3, having strictly homogeneous molecular weight, were studied. The crystal system of every melt crystallized oligourethane was similar to that of the single crystal of n = 2. In the case of n = 2, crystalline rearrangement by annealing does not occur, although the number of hydrogen bonds increases. On the other hand, rearrangement occurs for n = 3 and higher oligomers. It was considered that the rearrangement for n = 3 was the transformation from the spherulite to the plate-like crystal, whilst for those of n = 6 and 8 the growth of the new spherulitic type of crystal by secondary crystallization occurs. For n = 10 and the polymer crystal the thickening was accompanied by an increase of ordered regions.