Synthesis, characterization, and crystallization of model, semi-crystalline polymers: Influence of hydrogen-bonding

In order to better understand structure-property relationships, semi-crystalline polymers were synthesized, and the influence of hydrogen-bonds, heteroatoms, and uniformed lamellar thickness were examined. Literature procedures were modified, optimized, and then used to synthesize long-chain α,ω-diols containing up to 46 consecutive methylene groups. Melt polyadditions of these diols with short, aliphatic α,ω-diisocyanates produced a series of polyethylene-like polyurethanes whose hydrogen-bonding densities were systematically decreased. The hydrogen-bonds (or perturbations) were located at regular and controlled distances. These model, polyethylene-like polymers were characterized in order to determine the influence of the perturbations to the aliphatic backbone on the physical, thermal, and morphological properties of these polymers. The increasingly long-chain polyurethanes displayed physical and thermal characteristics (including melting point, lamellar stacking periodicity, and solubility) typical of polyethylene despite the presence of hydrogen-bonding. Crystallization studies showed that, although diluted, hydrogen-bonding still controlled the crystallization process of these polyethylene-like polymers. This resulted in analogous crystal structures and morphologies as polyamides and polyurethanes containing higher hydrogen-bonding densities. The effect of further perturbations, caused by heteroatoms on the aliphatic backbone, where also investigated with an emphasis on the resulting thermal properties of the polymers. The heteroatoms (oxygen and sulfur) caused a decrease in the melting temperature of the polymers without affecting the decomposition temperature or crystal structure. Ongoing research focuses on chemically controlling the lamellar thickness in order to engineer polyethylene-like crystals with hydrogen-bonding sites on the surface