CORRELATION OF BINDER MECHANICAL-PROPERTIES WITH FUNCTIONALITY TYPE AND MOLECULAR-WEIGHT DISTRIBUTION FOR HYDROXY-TERMINATED POLYBUTADIENES- C-13-NMR AND SEC STUDIES

Hydroxy-terminated polybutadiene (HTPB) liquid prepolymers (I-IX), wit h closely similar OH values, M(n)BAR, viscosity, and microstructure, w ere synthesized by H2O2-initiated free-radical polymerization of butad iene in an isopropanol-water solvent system. However, binders obtained by curing HTPB polymers showed wide variations in their sol content, cross-link density, and mechanical properties. These variations were a ttributed to the differences in functionality-type distribution (FTD) and molecular weight distribution (MWD) of the polymers. FTD was inter preted in terms of H [ HOCH2 - CH = CH - CH2 approximately approximate ly approximately) , V (HOCH2 - CH (CH = CH2)approximately approximatel y approximately approximately], and [GRAPHICS] primary hydroxyls. [ V/ G ] showed excellent linear correlation with the elongation at break ( E) of the binders. The polymers exhibited bimodal MWD and this behavio r was discussed in relation to two different initiation processes occu rring. The high molecular weight fraction (F(h)) of the various polyme rs was determined by reverse-phase HPLC and showed good correlation wi th E. The sol content and cross-link density of the binders also showe d good correlation with the parameter V/GF(h). The parameters [ V/G ] and F(h) provide acceptance criteria for blending different batches of polymers for propellant formulations.