A series of linear, aliphatic m,n-polyurethanes [O−(CH2) m −O−C(O)−NH−(CH2) n −NH−C(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 long-chain, 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 (∼75%) of hydrogen bonding in these polyurethanes even in the melt.

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The crystallization behavior of functionalized polymethylene chains with carbamate esters placed periodically between alternating docosyl and octyl segments has been examined with infrared spectroscopy. Specific features of both the interactions and the chain conformation have been found. The crystallization kinetics, including the induction period, can be followed with time-resolved infrared spectroscopy (5 s time resolution) and occurs in three stages. The kinetics of local hydrogen-bonding rearrangement is quite different from the kinetics of methylene chain stem ordering. The interchain interactions are characterized by a broad distribution of states. The initial melt consists of highly interacting chains (75% hydrogen bonded). During crystallization, this broad asymmetric ensemble of interacting states changes continuously to one dominated by that characteristic of the ordered structure. Even with the time resolution achievable, the specific features of a crystallite nucleus could not be captured.

Aliphatic 22,12-polyurethane has been crystallized directly from the melt and isothermally at 105 °C from N,N-dimethylformamide to give chain-folded lamellae of thickness ≈ 14 nm. The crystals have been investigated using X-ray diffraction, electron microscopy (imaging and diffraction), and computer modeling. The diffraction data was used to establish that the chains crystallize in a single-chain, triclinic unit cell, and the structure bears a strong resemblance to chain-folded lamellar crystals of even-even nylons. The results show that, even for a molecule with relatively long alkane segments, the hydrogen bonds exercise a controlling influence on the crystallization process and crystalline structure. Two models were investigated: one based on an analogy with nylon 6 6 and the other derived using molecular dynamics; they both turned out to be closely related. The model generated using molecular dynamics predicted localized rotations at the termini of the ester-amide coupled units. The resolution of the experimental data was not sufficient to clearly delineate between the two models, but the separate calculations do provide an estimate of the tolerances that can be accepted.

Long‐chain heteroatom‐containing telechelic diols with 29–32 atoms in the backbone were synthesized by a one‐step, free‐radical telomerization of 10‐undecene‐1‐ol with commercially available α,ω‐dithiols. The oxygen and sulfur atoms caused a decrease in the melting point and enthalpy of the diols, compared to the corresponding purely aliphatic diols. The heteroatom‐containing α,ω‐diols HO(CH2)11S(CH2)2X(CH2)2S(CH2)11OH, where X = CH2, O, or O(CH2)2O, were reacted in the melt with 1,6‐diisocyanatohexane OCN(CH2)6NCO, producing a series of polyurethanes containing an increasing amount of heteroatoms. Characterization by differential scanning calorimetry, infra‐red spectroscopy, thermogravimetric analysis, and wide angle x‐ray scattering of the m,n‐polyurethane series showed that, like the telechelic diols they were synthesized from, the heteroatoms caused a decrease in the melting point and enthalpy. However, they did not affect either the decomposition temperature or the crystal structure/packing.Typical decomposition behavior of all the heteroatom‐containing m,6‐polyurethane.magnified imageTypical decomposition behavior of all the heteroatom‐containing m,6‐polyurethane.