Polymerization Of Halide Substituted Styrenes Catalyzed By Half-Sandwich Scandium Complexes

Synthesis of halide substituted syndiotactic polystyrene has been a long-standing interest both in academic and industrial community,because it may afford functionalization of polymeric materials having excellent property of syndiotactic polystyrene which makes up the lack of functionality of polystyrene simultaneously,especially further improve the surface properties,flame retardant and heat resistance of materials.In this paper,the polymerization of halide substituted styrene?XSt?and the copolymerization of halide substituted styrene with styrene and ethylene were investigated by use of half-sandwich scandium complexes.The half-sandwich scandium complexes serve as an excellent catalyst for the the syndiotactic polymerization of halide substituted styrene and its copolymerization with styrene and ethylene to afford a new family of functionalized syndiotactic polystyrene materials.1.The homopolymerization of halide substituted styrene can be catalyzed by half-sandwich scandium complexes?C₅Me₄SiMe₃?Sc?CH₂SiMe₃?₂?THF??1?and?C₅Me₄SiMe₃?Sc?CH₂C₆H₄NMe₂-o?2?2?with high activity?>104 g polymer mol Sc-1h-1?.The structure of the catalysts,the types and location of halide group on the aromatic ring can significantly influence the polymerization activity and selectivity.The THF-free aminobenzyl scandium complex 2 can serve as a high active catalyst for the syndiotactic polymerization of XSt to afford highly syndiotactic poly?XSt??XSt = p,o,m-ClSt,p-FSt and p-BrSt??rrrr> 99%?with high molecular weight?>104 g mol-1?.The THF-containing trimethylsilylmethyl scandium complex 1 also shows high activity for the polymerization of XSt,however,to afford atactic poly?XSt??XSt = p,o-ClSt and p-BrSt?,syndiotactic poly?m-ClSt?and the mixture of syndiotactic and atactic poly?p-FSt?.The results show that the electropositivity of the scandium metal center and the electron cloud density of the benzene ring carbon play an important role in the selectivity of XSt polymerization.2.The complexes 1 and 2 also serve as excellent catalysts for the copolymerization of XSt and styrene with high activity(>105 g polymer molSc^-1h^-1)to afford novel copolymer materials with controllable composition and sequential structure.The copolymerization of XSt with styrene by use of complex 1 afforded multi-block copolymers containing syndiotactic polystyrene blocks and atactic poly?XSt?blocks.The copolymerization of XSt with styrene by use of complex 2 afforded random copolymers containing XSt?styrene sequences and syndiotactic styrene-styrene sequences or syndiotactic XSt-XSt sequences.Both XSt and styrene have the same coordination features in the complex 2 catalytic system,that is,there are interactions between the aromatic group of the last enchained unit and the scandium metal centre.While,their coordination features in the complex 1 catalytic system is different.So,the copolymerization of XSt and styrene afforded random copolymers in the presence of complex 2,while block copolymers in the presence of complex 1.The composition of the XSt?styrene copolymers can be controlled in a wide range by changing the feed ratio of XSt and styrene.3.The copolymerization of XSt with ethylene has been achieved by use of complexes 1 and 2 with high activity(>10⁵ g polymer molSc^-1h^-1)to afford p-FSt-ethylene and p-BrSt-ethylene random copolymers.The composition of the copolymers can be controlled in a wide range by changing the amount of p-FSt and p-BrSt at room temperature and pressure.The copolymers contained blocks of poly?p-FSt?or poly?p-BrSt?when the content of p-FSt or p-BrSt in the copolymers is higher than ethylene content.The blocks of poly?p-FSt?or poly?p-BrSt?in the copolymers prepared by 1 were atactic and the blocks of poly?p-FSt?or poly?p-BrSt?in the copolymers prepared by 2 were syndiotacitc.