EFFECT OF REACTIVITY OF DIFFERENT TYPES OF HYDROXYL-GROUPS OF HTPB ONMECHANICAL-PROPERTIES OF THE CURED PRODUCT

The amount of three types of hydroxyl functional groups (G(OH), H-OH, and V-OH) in hydroxyl terminated polybutadiene (HTPB), remaining in sa mples acetylated to the same extent under two different conditions, vi z., fast acetylation using acetyl chloride in presence of N-methyl imi dazole catalyst and slow acetylation by acetic anhydride, differed sig nificantly. For the fast acetylation there is a uniform reduction in a ll the three types of hydroxyls, probably because the reaction becomes random at rapid rates and the reactivity of the different types of hy droxyls does not play a major role. However, in the slow reaction, the reduction of G-type hydroxyls was 30% more than the expected value an d there was a corresponding increase in the amount of V-type hydroxyls remaining in the acetylated product, showing reactivity of OH in the order of G > H > V. When the reaction is slow, it becomes selective an d the change in reactivity of the three types of OH groups is reflecte d in the extent of conversion. The mechanical properties and the cross link density data show a reduction in the samples containing lesser am ounts of G(OH), confirming the branching nature of G(OH), which is inv olved in the crosslinking reaction. (C) 1997 John Wiley & Sons, Inc.