Controllable Synthesis Of Hydroxyl Functional Polybutadiene Liquid Rubber Via Oxidolysis Of Butadiene Rubber

Liquid rubber is a transparent oligomer and widely applied to adhesive, sealant, coating, elastomer, aerospace and etc. owing to its well processability, high solid content, and excellent physic and chemical properties. In the family of liquid rubber, hydroxyl terminated polybutadiene (HTPB) is a low-molecular-weight, telechelic, translucent liquid rubber which has a wide range of applications especially in the binder system of composite solid propellants. Commercial HTPB was synthesized via conventional free radical or anionic polymerization of 1,3-butadiene using a symmetrical difunctional initiator. However, it was difficult to control the microstructure of resultant HTPB precisely which limited its application area severely. Since the rapid development of aerospace and high-speed train, it was getting more and more crucial to prepare liquid rubber with a specific microstructure to meet the advanced requirement.This work aimed at the controllable synthesis of HTPB and its derivatives with high cis-1,4 content originated from the oxidolysis of domestic brand butadiene rubber (BR 9000). First, the oxidolysis process of slab butadiene rubber with mCPBA/periodic acid as oxidant was systematically studied, which afforded the successful synthesis of ATPB with high cis-1,4 content, controllable Mw and relatively narrow PDI in one-pot. The reduction reaction by NaBH4 was then carried out in order to obtain HTPB. On the basis of the above results, industrial original BR solution was used to synthesize HTPB by a more efficient and economic route. Second, epoxidized HTPB (EHTPB) and multi-hydroxyl polybutadiene (MHPB) with high cis-1,4 content, controllable molecular weight and functionality were firstly synthesized by tuning stoichiometric ratio of mCPBA and periodic acid. Third, linear hydroxyl terminated polyethylene (HTPE) and multi-hydroxyl polyethylene (MHPE) with regular PE segment were prepared via hydrogenation of HTPB and MHPB with TSH/TPA. The major achievements of this thesis as follows:(1) By taking slab butadiene rubber as raw material, the oxidolysis process including epoxidation reaction and chain-cleavage reaction was systematically studied. By tuning chain-cleavage percent equal to epoxy percent, ATPB was successfully synthesized via a two-step method or one-pot method without any isolation. Along with epoxy percent increasing from 0.63% to 12.0%, the Mn of resultant ATPB decreased from 12550 to 1410 g/mol, while the PDI was relatively narrow ranging from 1.3 to 2.0. In a mild condition, aldehyde groups were reduced by NaBH4 and HTPB obtained was a telechelic liquid rubber with cis-1,4 content of 95.7% and functionality of 2.0. The initial decomposing temperature in N2 atmosphere was 325℃ and glass transition temperature was -104.6℃. HTPB was a Newtonian fluid with positive correlation between the shear stress and shear rate and its viscosity was about one-tenth of FHTPB with a similar Mn. The viscosity of HTPB with Mn of 5500 g/mol at 40℃ was as low as 243.5 mPa·s.(2) By using industrial origin BR solution as raw material and 6# solvent-extracted oil or n-hexane as supplementary solvent to tune the BR concentration, HTPB could be well prepared with the BR concentration ranging from 50 to 100 g/L under sufficient mass transfer. Meanwhile, many high energy-cost and time-consuming processes, such as steam agglomeration and drying in BR production, and cutting, swelling and dissolving of slab rubber during the preparation of HTPB, can be removed. In short, this process was more economic, efficient and controllable.(3) On the basis of oxidolysis process for synthesizing HTPB, epoxidized ATPB (EATPB) with high cis-1,4 content was readily prepared via tuning stoichiometric ratio of mCPBA and periodic acid. The Mn of EATPB depended on chain-cleavage percent while the residual epoxy percent lied on different value between designed epoxy% and designed chain-cleavage%. PDI of EATPB was relatively narrow ranging from 1.5 to 2.0. The subsequent reduction reaction was carried by NaBH4 or Red-Al to synthesize EHTPB or MHPB respectively. For EHTPB, epoxy groups kept unchanged in the polymer chains. For MHPB, epoxy groups and-CHO were reduced to -OH groups simultaneously. EHTPB and MHPB possessed well controlled molecular weight, functionality, regular microstructure (cis-1,4> 95%) and relatively narrow PDI due to the controllable oxidolysis process. The initial decomposing temperature in the N2 atmosphere was over 300℃ and glass transition temperature ranged from -98.6 to -84.2℃ depending on the polarity and quantity of functional groups. The higher polarity and more functional groups, the higher glass transition temperature.(4) Linear hydroxyl terminated polyethylene (HTPE) and multi-hydroxyl polyethylene (MHPE) were successfully synthesized by the hydrogenation of HTPB and MHPB with TSH/TPA at 135～140℃ refluxing for 4 h. Due to the highly regular microstructure of HTPB and MHPB, the ethyl branching degree of HTPE or MHPE was as low as 4.2 branches/1000C, while the ethyl branching degree of FHTPE was up to 50.0 branches/1000C. Consequently, for HTPE and MHPE, the degree of crystallinity was 69.9% and 47.3%, the melting point was 123.2℃ and 110.9℃, respectively. After hydrogenation, the thermal stability of products was improved greatly and the initial decomposing temperature of HTPE and MHPE were 410℃ and 390℃ respectively in the nitrogen atmosphere.