Syndiospecific Polymerization Of Si-H-Functionalized Styrenes Catalyzed By Half-Sandwich Scandium Complexes

Syndiotactic polystyrene（s PS）is a promising engineering plastic with potential applications in the automobile,electronics and aerospace.However,the lack of functional groups in sPS has always restricted its practical application.Therefore,achieving the functionalization of sPS has been a research hotspot in recent years.In this paper,the homopolymerization of three Si-H-functionalized styrenes（FSt）,that is,p-methylsilylstyrene（FSt-1）,p-dimethylsilylstyrene（FSt-2）and p-diisopropylsilylstyrene（FSt-3）,and the copolymerization with styrene catalyzed by half-sandwich scandium complexes were studied respectively,preparing a series of Si-H-functionalized sPS with different structures.By converting Si-H groups into other functional groups,s PS containing various functional groups was obtained.1.Four half-sandwich scandium complexes with different ligands,that is,（C₅H₅）Sc（CH₂C₆H₄NMe₂-o）₂（Sc-1）,（C₅Me₄SiMe₃）Sc（CH₂C₆H₄NMe₂-o）₂（Sc-2）,（C₅Me₄SiMe₃）Sc（CH₂SiMe₃）₂（THF）（Sc-3）and（C₅Me₄SiMe₃）Sc（CH₂C₆H₅）₂（THF）（Sc-4）,and three styrene derivatives with different Si-H groups,that is,p-methylsilylstyrene（FSt-1）,p-dimethylsilylstyrene（FSt-2）and p-diisopropylsilylstyrene（FSt-3）,were synthesized respectively,investigating the effect of catalyst structures and Si-H structures on syndiospecific polymerization of styrene.Among them,the quasi-living polymerization of three FSt under the Sc-4 catalyst system was realized,preparing a series of Si-H-functionalized sPS（poly（FSt））with adjustable Si-H content,controlled molecular weight and narrow molecular weight distribution.2.The copolymerization of three FSt with St was respectively achieved under Sc-4catalyst system with the copolymerization activity above 113 kg polymer mol_Sc^-11 h^-1,preparing a series of syndiotactic FSt-St copolymers with adjustable composition,controllable molecular weight and high melting point（225^oC or so）,in which the FSt was distributed along the sPS backbones in a random manner.In addition,under the same experiment conditions,the sequencial block copolymerization of FSt-2 with St by sequential monomer feeding process was realized,preparing a series of Si-H-functionalized triblock copolymers（FSt-2/St/FSt-2）with high melting point（260^oC or so）,controlled molecular weight,adjustable Si-H content and block length.3.Three Si-H-functionalized sPS,that is,poly（FSt-1）,poly（FSt-2）and poly（FSt-3）were modified respectively by the hydrosilylation reaction.Among them,the Si-H group in poly（FSt-2）behaved as well in hydrosilylation reaction,and was converted into other functional groups quantitatively and controllably.Therefore,the various functional groups could be introduced into sPS by efficient hydrosilylation reaction,preparing epoxy-functionalized s PS with high melting point and nitro-spiropyran-functionalized sPS with photochromism property.