Complex Molecular Motions in Bulk Hard Segment Polyurethanes - A Deuterium NMR Study

摘要

Solid state deuterium NMR spectroscopy is used to characterize molecular motion in two specifically deuterated polyurethane hard segment polymers. The polyurethanes consist of 4,4'-diphenylmethane diisocyanate (MDI) chain extended with (2,2,3,3-d subscript 4) butanediol (BD0), and 2,4 toluene diisocyanate (TDI) chain extended with (2,2,3,3-d subscript 4) butanediol. Lineshape and relaxation T subscript 1 data were obtained as a function of temperature. The results indicate a broad distribution of motional correlation times, in both materials. In the semicrystalline MDI-BDO polymer, the distribution divides cleanly into two components that are attributable to the crystalline and amorphous regions of the material. In the TDI-BDO polymer, there is only a single broad distribution in keeping with the completely amorphous nature of this material. The results also show that the predominant large-scale motion of the alkyl chain is a gauche-trans conformational hop. The central methylene carbons of the butanediol undergo librations about their equilibrium positions, in addition to the large scale conformational transitions. Above approx. 60 C, additional larger-scale diffusion of the entire butanediol moiety occurs within a cone of semiangle approx. 15. The results are consistent with the existence of kinked conformations in the alkyl chain of this material. (Author)