Preparation of Hydroxyl-Terminated Polybutadiene with High Cis-1,4 Content

Abstract

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...

Facile access to carboxyl‐terminated polybutadiene and polyethylene fromcis‐polybutadiene rubber

“…Starting from the previously reported aldehyde‐terminated polybutadiene (ATPB), which has controllable molecular weight and high cis ‐1,4 content, CTPB was now prepared by selective oxidation. Several oxidants, such as H 5 IO 6 /PCC, were tested, but the oxidation of CC double bonds was inevitable.…”

“…FCTPE is the carboxyl‐terminated polyethylene obtained by hydrogenation reaction of FCTPB (obtained by free‐radical polymerization). Aldehyde group‐terminated polybutadienes (ATPB) were prepared according to our previous procedure . Jones reagent, a solution of chromium (VI) oxide in water and concentrated sulfuric acid (4 mol/L with respect to oxygen), was prepared according to previous reports .…”

“…Carboxyl‐terminated polybutadiene (CTPB) was prepared by selective oxidation of corresponding ATPB using Jones reagent, which was synthesized in one‐pot reaction according to our previous procedure, including the epoxidation of polybutadiene rubber by m CPBA and the subsequent oxidative cleavage of epoxy groups by H 5 IO 6 . For example, in ATPB2, the number 2 represents the molar ratio of the initial m CPBA/BD units in polybutadiene rubber (designed epoxy ratio).…”

“…The controlled degradation of polydienes by oxidative chain scission or by metathesis of butadiene rubber and natural rubber provided another approach for the preparation of telechelic liquid rubber . In our previous studies, various HTPBs characterized by high cis ‐1,4 content, controllable molecular weight and extremely low glass transition temperature have been prepared by selective oxidolysis of commercial cis ‐polybutadiene rubber followed by reduction …”

Hydroxyl Terminated Polybutadiene: Chemical Modification and Application of these Modifiers in Propellants and Explosives

“…The literature [10,[24][25][26][27] reveals that some factors, including the contents of cis-, trans-, vinyl-isomers, the molecular weight and molecular weight distribution have a great influence on the physicochemical properties of HTPB. Certainly, through a proper choice of the polymerization methods and careful adjustment of the reaction conditions, the chain microstructure can be controlled in order to obtain a HTPB binder pre-polymer with better properties [28][29][30]. However, due to the inert and non-polar nature of HTPB, some drawbacks exist in HTPB, such as its low energy and poor compatibility with highly energetic components, which limit its further application in propellants or explosives.…”