Modeling of Hydroaxyl Terminated Polybutadiene Prepolymer Based Polyurethane Networks

Abstract

Hydroxyl Terminated PolyButadiene (HTPB) prepolymer has been considered as a work-horse resin for modern high energy solid propellants because of its higher hydrocarbon content of the polybutadiene chain, low viscosity, low cost, easy processing characteristics, higher solid loading, higher mechanical properties, improved burning rate characteristics and better ballistic performance. The processing characteristics of composite solid propelIants depend on the rheology of the total mass of the system which is influenced by the nature of the polymer or prepolymer back­ bone, the nature of its functional groups, its chain length, average molecular weight and molecular weight distribution, average functionality and functionality distribution, apart from its viscosity. In the HTPB prepolymer based propellant curing process, urethane linkages are formed. These polyurethanes of desired properties are tailor made by controlling the concentration and the ratio of the reactants i.e. HTPB prepolymer, chain extender (1,4-butanediol), crosslinker (trimethyloI propane) and curator (toluene diisocyanate). In the present study, HTPB prepolymers of widely varying molecular weight and functionality distribution were used for the formation of polyurethane networks. The properties like sol content, crosslink density (Ve) and effective chain length (LX) of the formed networks were calculated by using the models of Marsh, and of Macosko and MiIler, for which the input parameters required are functionality distribution and equivalent weight of the polymer (or prepolymer), extent of reaction (PA) and density of the cured network.