Hydroxyl-terminated polybutadiene (HTPB) with high cis-1,4 content (>95.0%) has been prepared via a two-step method by taking commercial butadiene rubber (BR9000) as a starting material, including the one-pot synthesis of aldehydegroup-terminated polybutadiene (ATPB) in high efficiency and the subsequent reduction reaction. The double bonds distributed in linear polybutadiene were first epoxidized and then cleaved at the exact epoxidized sites. The epoxidation reaction by 3-chloroperbenzoic acid and chain-cleavage reaction by periodic acid are controllable, highly efficient, selective, and quantitative. Along with an epoxy percent increase, the molecular weight of ATPB prepared via a one-pot method decreased with a relatively narrow polydispersity index. The aldehyde groups in the chain ends were reduced by NaBH 4 to produce HTPB, in which the high cis-1,4 content of BR was retained. INTRODUCTIONHydroxyl-terminated polybutadiene (HTPB) and modified HTPB are important telechelic liquid rubbers that are widely used in the binder system of composite solid propellants. 1−6 Because of its unique properties, such as hydrolytic stability, resistance to aqueous acids and bases, adhesion to a variety of substrates, high processability with high solid loading, lowtemperature flexibility, electrical insulation properties, and high elongation with good elastic recovery, 7 HTPB is widely used not only in propellant applications but also in other areas, such as membranes, adhesives, coating, sealants, newer materials, etc. The reactive functional groups in the terminated liquid rubber could also be applied to build ABA triblock copolymers, 8−10 toughened resins, 11,12 elastomers, 13−17 cross-linked elastomers, 18 and supermolecular polymer gels. 19−21 It is well-known that the properties of HTPB are greatly affected by its chain microstructures. 7 Lower 1,2-vinyl content will lead to lower viscosity of HTPB, and the mechanical properties, such as tensile strength and elongation at break, are enhanced with an increase in the 1,4 content. Furthermore, the higher the 1,4 content, especially higher cis-1,4 content, the lower the glass transition temperature and the better the lowtemperature flexibility. 22 Thus, because of its lower viscosity, good mechanical and thermal properties, and low-temperature flexibility, HTPB with high cis-1,4 content might be the best choice for the preparation of new materials with high processability and high elasticity.HTPB was conventionally prepared by free-radical polymerization 23 and anionic polymerization 22 of 1,3-butadiene using a bifunctional initiator. The microstructure, molecular weight, and molecular weight distribution of HTPB were affected by the type of initiator, polarity of the solvent, and polymerization temperature. According to the literature, 23 HTPB prepared by free-radical polymerization had a maximum 79% of 1,4 content, a degree of functionality of 2.1−2.3, and a polydispersity index (PDI) near 2.0. The anionic polymerization process produced HTPB with a maximum 90% of 1,4...
A series of polyurethanes have been prepared from hydroxyl-terminated polybutadiene (HTPB) with high cis-1,4 content and commercial free-radical-polymerized HTPB (FHTPB). The mechanical properties of cured polyurethane (PU) samples have been studied by tensile testing and dynamic mechanical analysis (DMA), and their thermal properties have been tested by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The NCO/OH ratio, chain extension coefficient (r), and microstructure of HTPB and FHTPB have a large influence on the mechanical properties of PUs. Meanwhile, the cyclic tensile testing indicated that the HTPB-based PUs had an outstanding elasticity. Both DSC and DMA analyses showed that the HTPB-based PUs had a glass transition temperature much lower than that of the FHTPB-based PUs. The hydrophobicity of the surface of PUs was verified by measuring their water contact angles.
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