Polymerization Of 4-(2,2?-diphenylethyl) Styrene By Half-Sandwich Scandium Complexes

It is of great significance to synthesize graft copolymers with a controllable backbone and a wide variety of branches by combining the advantages of coordination and free radical polymerization.In this paper,taking full advantage of the high activity and selectivity of the half-sandwich scandium complexes to syndiospecific polymerization of 4-(2,2'-diphenylethyl)styrene(DPES)and its copolymerization with other olefins(isoprene,styrene,ethylene).A series of containing active free radicals copolymers with controllable composition have been successfully synthesized.1.The ligand structure of scandium complexes has a great influence on the activity and selectivity of DPES homopolymerization.The half-sandwich scandium catalysts C₅Me₄SiMe₃Sc(CH₂SiMe₃)₂(THF)(1)and C₅Me₄SiMe₃Sc(CH₂C₆H₄NMe₂-o)₂(2)with a steric hindrance ligand showed high activity(170.6 kg polymer/(mol Sc·h))and excellent syndiotacticity(rrrr=99%)for the homopolymerization of DPES;The activity of the THF-containing scandium complex 1 is higher than THF-free scandium complex 2;The half-sandwich scandium catalyst(C₅H₅)Sc(CH₂C₆H₄NMe₂-o)₂(3)with a small ligand can also catalyzed the syndiotactic homopolymerization of DPES.However,the polymerization activity and syndiotactivity are lower than that of 1 and 2.The obtained DPES syndiotactic homopolymer has a glass transition temperature(T_g)at 86°C;The molecular weight of syndiotactic DPES homopolymer can be controlled by changing the ratio of DPES and scandium complex;Syndiotactic DPES homopolymer can generate free radicals when heated at 90?,and the free radicals can initiate the polymerization of methyl methacrylate(MMA)to obtain the DPES-MMA graft copolymers.2.The copolymerization of DPES with isoprene(IP),styrene(St)or ethylene(Et)by using half-sandwich scandium complexesto afford a series of copolymers containing active free radicals.In the copolymerization of DPES with IP,the ligand structure of scandium complexes directly influenced the copolymerization activity,selectivity and the sequence structure of DPES-IP copolymers.The copolymerization of DPES with isoprene(activity up to 55.3 kg polymer/(mol Sc·h))by using scandium complex 2 afforded DPES-IP gradient copolymers with controllable molecular weight and composition.These DPES-IP copolymers contained 1,4-and3,4-IP(ratio is 70/30)and syndiotactic poly(DPES),and the copolymerization.The copolymerization of DPES with isoprene(activity 7.4 kg polymer/(mol Sc·h))by using scandium complex 3 afforded tapered DPES-IP copolymers with controllable molecular weight and composition.The tapered DPES-IP copolymers contained 1,4-and 3,4-IP(ratio is 96/4)and syndiotactic poly(DPES),The copolymerization of DPES and St(activity up to 234 kg polymer/(mol Sc·h))by using scandium complexes 1 and 2afforded the random DPES-St copolymers with controllable molecular weight and composition.The syndiotactic selectivity of DPES is greatly reduced in the copolymerization of DPES and St.The copolymerization of DPES with Et(activity up to 558 kg polymer/(mol Sc·h))by using scandium conplexes 1 and2 afforded the random DPES-Et copolymers with controllable composition and high molecular weight.