| The polyurethane has been developed very fast since its discovery because of its excellent performance. And the polyurethane made from the hydroxyl terminated polybutadiene (HTPB) is often used as the main components of soild propellants, so it is very important to the national defence and military project. With the development of science and technology, it also proposes higher request of HTPB-based polyurethane. However, most of HTPB-based polyurethanes are based on free-radical polymerized HTPB (FHTPB) and their properties are difficult to be improved. A new kind of HTPB (DHTPB) with high cis-1,4 content obtained from the degradation of polybutadiene rubber was used as the main material to prepare the polyurethane (DPU) in this work, and the relationships between structure and porperties of the DPU were also investigated.Firstly, three DHTPBs with different molecular weight were prepared by the degradation of polybutadiene rubber. The structures of DHTPBs and FHTPBs were compared. It has been found that ths cis-1,4 content of the DHTPBs was up to 96%, and the average hydroxyl functionality of DHTPBs was 2.0. As compared to the DHTPB, the the cis-1,4 content of FHTPBs and the average hydroxyl functionality were 22% and 2.3, respectively.Secondly, the DPUs were prepared from the DHTPB,4,4’-diphenylmethane diisocyanate (MDI) and 1,4-butanediol. The effects of NCO/OH ratio and the chain extension coeffient on the mechanical properties were studied. It has been found that the NCO/OH ratio in the feed of DPUs could affect the hard segment content of the DPU and the chain extension coeffient controlled the chain length of the DPU, so the NCO/OH ratio and the chain extend coeffient can influence the mechanical properties of DPUs. And when NCO/OH ratio and chain extension coeffient were 1.6 and 0.8 respectively, the DPU’s mechanical properties were best. What’s more, the cyclic tensile tests showed that the elasticity recovery of DPUs was excellent.Thirdly, comparing with FPU, the tensile strength and the elongation at break of DPU were three times higher than those of FPU, which was probably ascribed that the the 2.3 of average hydroxyl functionality of FHTPB resulted in the flaws in the chain structure of FPU. The glass transition temperature (Tg) of the DPUs was-104℃ and the Tg of FPUs was-78℃ (determined by DSC), which showed that the DPU could be applied in the colder environment. Both DPU and FPU have hydrophobic surfaces with water contant angles over 100℃. Due to their similar type and number of groups, DPU and FPU have silimar thermal degradation properties with three stages, starting from about 180℃.Finally, the epoxidized HTPB (EHTPB) was prepared by the epoxidation of DHTPB, and used for the preparation of polyurethane (EPU). And the effect of the epoxy percent in EHTPB on the properties of EPU was studied. As the increase in the epoxy percent, the Young’s modulus and the tensile strength of EPU increased, whereas the elongation at break decreased. And EPU, prepared from the EHTPB with 10% of epoxy percent, had the best mechanical properties with 8.82 MPa of Young’s modulus,7.83 MPa of tensile strength, and the 485±23% of elongation at break. What’s more, the the elasticity recovery of EPU was slightly better than DPU. The results with TGA test showed that the thermal degradation progress of EPU could be divided into three stages, which was also similar to DPU. However, the EPU had better thermal stability with the start-degradating temperature at 210℃, which was 30℃ higher than DPU. The DSC test showed that the Tg of EPU increased as the increase in the epoxy percent, however they were still lower than that of FPUs. |
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