Studies on functionality distribution of extractable sol from HTPB-isocyanate gumstock

Hydroxyl‐terminated polybutadiene (HTPB), even when cured with stoichiometric quantities of toluene diisocyanate (TDI), gives some extractable sol from the gumstock and the sol is believed to be predominantly due to the nonfunctional molecules in the HTPB. However, the present work shows that the molecules in the sol contain hydroxyl functional groups whose nature was established by hydrolyzing the urethane present in the sol and by analyzing the functionality distribution of the molecules so generated from the sol. The sol contains chain‐extending difunctional and crosslinking tri‐ and polyfunctional molecules; however, the concentration of the former is more, when compared to the original HTPB. All three types of primary hydroxyl groups of HTPB (G, H, and V) are also present in the sol. While there is a reduction in the G‐type hydroxyl in the sol, there is no major difference in the cis, trans, and vinyl contents of the backbone of the sol and HTPB. The molecules in the sol have been excluded from the crosslinked network, not only because of the lack of their functionality alone, but also as a result of network imperfections which are an integral part of nonlinear polymerization reactions. © 1995 John Wiley & Sons, Inc.