Abstract
Polyurethane elastomers are a numerous group of polymeric materials of wide practical application. They are usually formed by polyaddition of diisocyanates with hydroxyl-terminated polyesters or polyethers in the presence of low molecular weight diols or diamines as chain extenders. One may consider urethane elastomers to be block copolymers, consisting of moderately flexible long linear polyester or polyether segments and relatively stiff segments of aromatic and urethane groups. The length and structure of each block can be easily controlled. Crosslinking by an excess of diisocyanate can occur only at the stiff segments, and the number of branch points can also be controlled. The properties of these elastomers can be widely changed using components of different structures and varying their quantitative ratios. They are the results of a combination of segment flexibility, crosslinking, chain entanglement, orientation of segments, hydrogen bonding and other van der Waals forces, as well as rigidity of aromatic units. In the urethane systems, hydrogen bonding and other van der Waals forces, play a much more pronounced role than in familiar olefin-derived elastomers. Although polyurethane elastomers have very good mechanical properties at room temperature, their application is strongly limited by rapid deterioration of properties which takes place at elevated temperatures. The decay of mechanical properties of polyurethane is caused by the breaking of hydrogen and other secondary bonds, as well as by the presence of relatively weak crosslinks that make up their network. The properties of polyurethanes at elevated temperatures may, perhaps, be improved by forming additional crosslinks, besides the typical ones. Some efforts concerning this problem have been published. The aim of our study was to obtain and check the properties of polyurethane elastomers having unsaturated bonds, on which some additional crosslinks were expected to be formed in the presence of a suitable crosslinking agent.
Segmented Phase of Ultraviolet (UV) Curable Thermoset Polyurethanes-Graphite (TPU-G) Composites