Theoretical investigation on thermal aging mechanism and the aging effect on mechanical properties of HTPB-IPDI polyurethane

The thermal aging mechanism of hydroxy-terminated polybutadiene/isophorone diisocyanate (HTPB-IPDI) polyurethane was studied theoretically by density functional theory (DFT) method. The results of bond dissociation energy (BDE) calculated at B3LYP/6-311++G(2d,p) level show that the C-O bonds connected with the CH2 group are the weakest bonds. The weakest C-H bond was calculated by BDE method is the C-H bond in the alpha position connected with the ester group, and the secondary weak C-H bonds are in the cyclohexane tertiary carbon moiety whatever in model 1 or model 2. The HTPB-IPDI decomposition reactions toward the unsaturated cyclohexene, methyl carbamic acid, methylamine, and CO2 products were also calculated to be thermodynamically feasible. The mechanical properties changes of aged HTPB-IPDI polyurethanes were analyzed by molecular dynamic simulation. The aged HTPB-IPDI with CO2 molecules inside the cell had a decreased Poisson's ratio and bulk modulus, while that of the aged system with CO2 diffused out of the system tended to increase. The decreased Young's modulus and shear modulus are attributed to the hard segment dissociation and the hydrogen bond breaking in the HTPB-IPDI cross-linking network. (C) 2016 Elsevier B.V. All rights reserved.