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Synthesis and properties of hydroxyl-terminated polybutadiene-based polyurethanes reinforced with polyhedral oligomeric silsesquioxanes.

Polyurethane/polyhedral oligomeric silsesquioxane (PU/POSS) hybrid composites are prepared by a one-step PU reaction using hydroxyl-terminated polybutadiene (HTPB) prepolymer, isophorone diisocyanate (IPDI) and either non-reactive or reactive POSS molecule. The effect of incorporation of functionalized POSS molecules covalently bonded or physically blended into PU matrix is investigated in terms of mechanical reinforcement and thermal stability of these resulting PU/POSS hybrid composites. PU/POSS hybrid composites prepared with reactive POSS molecules exhibit the mechanical reinforcement while maintaining low glass transition temperataure (T(g)), probably due to the fact that reactive POSS molecules chemically incorporated in PU are aggregated to crystallize, effectively working as a physical crosslinking in PU/POSS hybrid composites. This can be advantageous in that mechanical reinforcement of PU/POSS hybrid composites can be achived without sacrificing the low temperature properties of these composites. However, the contribution of POSS molecules incorporated covalently into PU matrix is virtually absent on the thermal decomposition temperature (T(d,max)) measured using TGA/DTG. Thermal degradation behavior of these hybrid composites in the early stage rather appears to depend preferably on characteristics of POSS molecules incorporated.