Research On The Synthesis Of Amino-Functionalized Syndiotactic Polystyrene By Half-Sandwich Scandium Complexes

Syndiotactic polystyrene, as an engineering material with outstanding properties, has stimulated great interest both in academic and industry community. However, there are mainly two drawbacks which restrict the further practical use of sPS:(1) absence of the polar groups for adhesion to substrates and compatibility with polar polymers; (2) rigidity of the polymer chains, leading to sPS with poor toughness. Therefore, the research in functionalization of 5PS is very important for improving its property and expanding its application scope.In this work, we took advantage of the excellent characteristics of the half-sandwich rare earth catalysts, such as high activity, high stereoselectivity and single-site behavior, for the synthesis of amino-functionalized sPS, amino-functionalized butadiene-styrene copolymer and star amino-functionalized butadiene-styrene copolymer, obtaining a serious of functionalized sPS materials. The research results are as follows:1. Three amino-functionalized syndiotactic polystyrene were efficiently synthesized by the polymerization of p-N,N-dimethylaminostyrene (DMAS),p-N,N-diethylaminostyrene (DEAS) and p-N,N-diphenylaminostyrene (DPAS) by use of (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2. The syndiotacticity ([rrrr]) of poly(p-N,N-dimethylaminostyrene) (sPDMAS) was over 99%. The obtained three amino-functionalized syndiotactic polystyrene were all semi-crystalline polymers, in which the melting points (Tm) of sPDMAS and sPDEAS were 252? and 286?, respectively, while sPDPAS containing two Tm at 236?,289?. The research indicated that the drastic chain transfer reaction occurred in the polymerization of DMAS, and the chain transfer reaction was efficient restrained with the increase of the steric hindrance of amino substituents from dimethylamino to diethylamino. Amino-functionalized syndiotactic polystyrene, such as sPDMAS, was used as an effective polymer support for anchoring the palladium nanoparticles to synthesize novel sPDMAS-Pd nanocomposites, in which palladium nanoparticles were uniformly dispersed on sPDMAS matrix.2. A serious of amino-functionalized syndiotactic styrene-butadiene copolymers were synthesized with the copolymerization of three amino-functionalized styrene derivatives with butadiene by use of (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2. In the copolymerization of DMAS with butadiene, the molecular weights of the obtained DMAS-BD copolymers were bimodal distributions and chain transfer reaction existed in the copolymerization. In the copolymerization of DEAS with butadiene, the DEAS-BD multiblock copolymers were obtained in which the butadiene homosequences were primarily cis-1,4 (?85%) and the styrene chain segments were syndiotactic. The composition and molecular weigh of the copolymers could be easily controlled by tuning the molar ratio of monomers and monomer to catalyst. The molecular weights of the copolymers were unimodal distributions and chain transfer reaction was restrained in the copolymerization. The melting points of the copolymers gradually increased from 214 ? to 249? with the DEAS contents ranging from 30-97 mol%. In the copolymerization of DPAS with BD, DPAS-BD diblock copolymers were achieved with one-pot monomer addition and the block lengths were controllable. The butadiene homosequences were primarily cis-1,4 (?85%) and the styrene chain segments were syndiotactic in the diblock copolymers. The copolymers showed one glass transition temperature (Tg) at about -90? and two Tms at about 240? and 290?, respectively.3. Stereoregular star PB, star styrene-butadiene copolymer (St-BD) and star amino-functionalized styrene-butadiene copolymer (DPAS-BD) were synthesized through "arm-first" method with divinylbenzene complexes as cross linkers by use of (C5Me4SiMe3)Sc(CH2SiMe3)2(THF). On the synthesis of star PB, the effects of the polymerization parameters were studied systematically, including the molar ratio of [p-DVB]/[Sc], coupling reaction time, length of polybutadiene arm and structure of cross linkers. The star high cis-1,4-PB (cis-1,4:83%) were obtained with coupling efficiency of 50% and average arm number reached to 26.4. Star St-BD diblock copolymer was synthesized with coupling efficiency of 41% and average arm number of 16.5 with optimized coupling reation conditions, in which the butadiene homosequences were primarily cis-1,4 (83%) and the styrene chain segments were high syndiotactic ([rrrr]>99%). Furtherfore, Star DPAS-BD diblock copolymer was synthesized with coupling efficiency of 44% and average arm number of 18.3 by use of the scandium complexe, in which the PB chain segments were primarily cis-1,4 (85%) and the PDPAS chain segments were syndiotactic.