Synthesis Of High 1,4-unit Content Hydroxyl-terminated Polybutadiene By Anionic Polymerization

Hydroxyl-terminated polybutadiene (HTPB) is a telechelic liquid rubber containing hydroxyl groups. It was widely used as the binder for solid propellant of missiles and rockets due to its good mechanical property after curing. Recently, the synthesis of higher performance HTPB is highly desired because the shooting range of missiles has been progressively enhanced. It is well-known that the performance of HTPBs was greatly affected by their chain microstructures. For example, when increasing the content of 1,4-units, the glass transition temperature (Tg) of polybutadienes decreases, exhibiting a rubbery state. By contraries, polybutadienes exhibit a plastic state with decreasing the content of 1,4-units. In order to obtain higher performance HTPB, the high content of 1,4-units is considered as one of important molecular parameters.HTPB made by traditional radical polymerization (abbreviated as radical HTPB) has a maximum 1,4-unit content of 79% and a broad molecular weight distribution. In addition, its ill-defined hydroxyl distribution easily causes the nonuniform cross-linking network and worse mechanical properties. Although the living radical polymerization was extensively developed recently, the content of 1,4-units still has not improved. On the contrary, HTPB made by anionic polymerization (abbreviated as anionic HTPB) can give high 1,4-unit content of 90%, narrow molecular weight distribution, and well-defined hydroxyl distribution in principle. These characteristics are very useful in improving the performance of HTPB. Therefore, the synthesis of anionic HTPB has attracted much attention.In recent years, mechanical property of HTPB as the binder for solid propellant of missiles and rockets demands to improvement with the development of aviation and space flight fields. The plants of HTPB are Lanzhou petrochemical corporation and liming research institute of chemical industry in our country, which have already realized industrialization in free-radical HTPB respectively but it is broad molecular weight distribution, undefined molecular weight and hydroxyl value, High Viscosity and wide gaps, especially obvious inferior in scale experiment that led to low-grade mechanical properties of HTPBs. The HTPB of very narrow molecular weight distribution (<1.05) and functionality of hydroxyl groups approached 2 are very imperative in military to fix model and future model solid propellant of missiles. More recently, we reported the synthesis of hydroxyl-terminated polyisoprene (HTPI) with 90% of 1,4-unit content by anionic polymerization, using a novel protective monofunctional initiator with good solubility in hydrocarbon solvent. To our knowledge, this is the highest content of 1,4-units among the reported HTPIs. In this research, our aim is to extend this method to synthesize the anionic HTPB, whose properties can meet the urgent requirements in advanced solid propellant.