A series of linear, aliphatic m,n-polyurethanes [O-(CH2)(m)-O-C(O)-NH-(CH2)(n)-NHC(O)](x) derived from long-chain aliphatic diols HO-(CH2)(m)-OH, where m = 12, 22, or 32, and much shorter diisocyanates O=C=N-(CH2)(n)-N=C=O, where n = 4, 6, 8, or 12, were previously characterized and shown to have physical and thermal properties similar to polyethylene. The current study shows, however, that hydrogen bonding still exercises a controlling influence on the crystallization process of these longchain, aliphatic polyurethanes. X-ray diffraction, electron diffraction, and infrared spectroscopy indicate that these long alkane segment polyurethanes have interchain and intersheet distances similar to that seen for polyamides and polyurethanes of higher hydrogen bonding densities. Hydrogen bonding controls the crystallization, packing, and morphology of these polyurethanes, resulting in a crystal structure analogous to that of aliphatic, even-even (syncephlic) polyamides and unlike that of polyethylene. Additionally, high-temperature infrared studies show the existence and high concentration (similar to75%) of hydrogen bonding in these polyurethanes even in the melt.