Estimation of the conformational characteristics of polyurethane chains

Abstract

Linear polyurethanes (PUR-Dk) were prepared by reacting 4,4'-methylenediphenyl diisocyanate (MDI) with low-molecular-weight diols HO-(CH,),--OH (k = 2, 3,4, and 6) and fractionated by precipitation or extraction with mixtures of N,N-dimethylformamide (DMF) and dibutyl ether (DBE). The fractions were characterized by their weight-average molecular weights aw (light scattering) and intrinsic viscosities [q] in DMF (good solvent) and mixtures of DMF with DBE (poor solvents). The Kuhn statistical segment length lK was evaluated from the intrinsic viscosities in poor solvents. Low values of lK, (12 to 14) x lo-' cm, indicate that benzene rings and virtual double bonds (urethane groups) confine neighbour interactions to bonds within the repeating units and assure independent rotations at the bonds adjoining them.

Constructing sacrificial bonds and hidden lengths for ductile graphene/polyurethane elastomers with improved strength and toughness

“…By combining with hydrogen-bond interactions, they could cause the partially ordered one-dimensional stacking of pyrene rings and further induce the formation of the corrugations in HO-GNs. Given the contour length of a pyrene ring containing a MDI molecule and a PEG oligomer molecule ($3.6 nm), 60,61 the formed corrugations are expected to consist of one or two rows of closely stacked pyrene ring aggregates. However, owing to the inherent disorder feature of GNs, the propagation of these pyrene aggregates along some direction could be interrupted or deflected so that some curved corrugations can be observed.…”