Molecular Dynamics Simulation of HTPB/Plasticizer Blends: Application to Calculating Miscibility and Glass Transition Temperature

By means of full atomistic molecular dynamics simulation, the solubility parameters for Hydroxyl terminated polybutadiene (HTPB) and plasticizers of dicapryl sebacate (DOS), dicapryl sebacate (DOA), pelargonic acid isodecyl ester (TOA), dibutyl phthalate (DBP) and dioctyl phthalate (DOP) have been calculated and the results are in agreement with the literature values. According to the theory of solubility parameter, the miscibility of HTPB and the selected plasticizers is well. Furthermore, the volume-temperature curves of pure HTPB and HTPB/plasticizer blends with varying plasticizer (DOS) content were simulated to obtain the glass transition temperature (T-g). The simulated T-g of pure HTPB is about 202 K, which is compared well with the experimental result. A linear dependence of the glass transition temperature on the plasticizer (DOS) content ranging from pure HTPB to a plasticizer molar proportion of 90% is found; likewise for other HTPB/plasticizer (TOA and DOP) blends (1:3 blends in term of repeated units), results indicated that blends have lower T-g compared with pure HTPB; while the effect of DOA and DBP on T-g is little. Based on miscibility and low temperature performance, it should be pointed out that DOS, TOA and DOP are better additives for HTPB than DOA and DBP.