Study On Butadiene/Isoprene/Styrene Star-comb Dendrigraft Polymer

The third class dendritic polymers, the dendrigraft polymers, combine features of dendrimers and hyperbranched polymers. The syntheses of dendrigraft polymers follow a generation-based growth scheme similar to dendrimers. Since the coupling reaction is a random process, the branched structure of dendrigraft polymers is similar to that of hyperbranched polymers. Utilization of polymeric chains as building blocks leads to a very rapid increase in molecular weight per generation, and the branched polymers with high molecular weight and narrow molecular weight distribution (MWD<1.50) can be produced in a few steps. As such, the dendrigraft polymers are increasingly a focus of widespread interests. Anionic polymerization is one of the most accurate and effective methods for the design of polymer architecture, though the synthesis of high molecular weight polymers is severely challenging due to its extremely sensitive to system cleanliness. The combination of anionic polymerization and coupling reaction for preparation of a high molecular weight and highly branched polymers with a controlled architecture is an important research direction. Recently, the dendrigraft polymers have been synthesized by grafting-onto method with a linear polymer chain serving as 'core' for the molecules, and its molecular topology is relatively simple.In this paper, star liquid polybutadienes were synthesized by the living anionic polymerization and coupling reaction, and then epoxidized by in situ peroxyformic acid. The epoxidized star liquid polybutadienes were refined until water and oxygen content below 10ppm to use as coupling agent for anionic polymerization system. A series of butadiene/isoprene/styrene star-comb homopolymers were successfully synthesized with the epoxidized star liquid polybutadiene as coupling agent, and the method has applied a Chinese patent; the star-comb butadiene/styrene block copolymers (SC-SBC) were prepared with the epoxidized star liquid polybutadiene as coupling agent, the impact performances of SC-SBCs are very excellent, and the method has applied a Chinese patent. Based on the philosophy of macromolecular design throughout the thesis, the author fully utilized the monomers of butadiene, isoprene, and styrene produced in bulk to synthesize a series of novel dendrigraft polymers with n-butyllithium as initiator, cyclohexane as solvent, THF as polar additives, epoxidized polymer as coupling agent. Following were the typical dendrigraft polymers prepared in this work, including the linear-comb dendrigraft polybutadiene, the star-comb dendrigraft polybutadiene, and the star-comb dendrigraft polyisoprene. In addition, the G0-G4 star-comb dendrigraft polybutadienes were hydrogenated by nickel naphthenate/3-isobutyl aluminum catalyst system to obtain G0-G4 star-comb dendrigraft polyethylenes. Furthermore, the molecular parameters,branching factors and thermal properties of the novel dendrigraft polymers mentioned above were thoroughly investigated.From the summary of the full thesis, it came to the main conclusions that:The linear and star liquid polybutadienes were synthesized by anionic polymerization and subsequent epoxidized by in situ peroxyformic acid method. Then the epoxidized liquid polybutadienes were refined and used as coupling agent for anionic polymerization system.A series of G0-G4 star-comb dendrigraft polybutadienes were successfully synthesized by cycles of epoxidation and coupling reaction with epoxidized polybutadiene as coupling agent and star polybutadiene as 'core'. The star-comb dendrigraft polybutadienes have narrow molecular weight distributions (MWD<1.23) consistent with a uniform molecular size and display geometric increases in molecular weight and branching functionality for successive generations. The branching factors decrease quickly as the increase of generation number. The molecular topology of the star-comb dendrigraft polybutadiene has a dense spherical structure. G4 star-comb dendrigraft polybutadiene has narrow MWD as low as 1.17, high molecular weight up to 1.4×10~7, branching functionality up to 3700, and branching factor as low as 0.0040.A series of G0-G4 star-comb dendrigraft polybutadienes were converted into the corresponding G0-G4 star-comb dendrigraft polyethylenes through the hydrogenation of polybutadienes. Catalytic hydrogenation was carried out with nickel naphthenate/ triisobutylaluminium system. The hydrogenation degrees of G0-G4 hydrogenated star-comb dendrigraft polybutadienes are as high as 99.0%. The star-comb dendrigraft polyethylenes exhibit certain degree of crystallinity and demonstrate certain degree of polarity, and are a class of good model polyethylene. G4 star-comb dendrigraft polybutadiene (M_w=1.8×10~7, f_w=6790), the highest molecular weight and most highly branched among G0-G4 star-comb dendrigraft polybutadienes, also has the bigger difficulty during hydrogenation. The hydrogenation degree of G4 hydrogenated star-comb dendrigraft polybutadiene is up to 99.5% and its degree of crystallinity is only 22.2%. Due to highly branched structure, G4 star-comb dendrigraft polyethylene has low melting temperature and crystallization temperature. Compared to G4 star-comb dendrigraft polybutadiene, the thermal stablity of G4 star-comb dendrigraft polyethylene has increased.A series of G0-G4 star-ccmb dendrigraft polyisoprenes were successfully synthesized by cycles of epoxidation and coupling reaction with epoxidized polyisoprene as coupling agent and star polyisoprene as 'core'. The star-comb dendrigraft polyisoprenes display geometric increases in molecular weight and branching functionality for successive generations. The branching factors decrease as the increase of generation number. The molecular topology of the star-comb dendrigraft polyisoprenes has a loose spherical structure. G4 star-comb dendrigraft polyisoprene has narrow MWD as low as 1.17, high molecular weight up to 3.6×10~6, branching functionality up to 765, and branching factor as low as 0.0091.The star-comb styrene/butadiene block copolymer was synthesized by anionic polymerization and coupling reaction with epoxidized star liquid polybutadiene as coupling agent. The notched izod impact strength of the star-comb butadiene/styrene block copolymer reaches as high as to 216J/m. The instrumented impact curve shows that the material is no fracture in 4ms.