Synthesis And Properties Of Functionalized Polystyrene Containing Spiropyran Group

Photochromic materials containing spiropyran(SP)group have potential applications in the field of smart materials due to their structural reverse ability of closed-loop(SP)to open-loop(MC)and the advantages of optically remote activation and precise control.As general polymer material,polystyrene(PS)is widely applied to improve the machinability and stability of functional materials.However,the PS blends and polymer photochromic materials doped with,or grafted/copolymerized by SP still have limitations,such as poor structural stability,poor controllability of molecular weight and polydispersity index(PDI),and insufficient regulation of photochromism.Therefore,the synthesis of polymers with controllable structures and tunable photochromism is of great significance for the research and applications of photochromic materials.Living anionic polymerization(LAP)possesses unique characteristics of living polymerization that can tailor the PS homopolymer or block copolymer templates with well-defined molecular weight and narrow polydispersity index.Combining with the efficient click reaction of functional modules,the functional polymers with controllable structure are prepared,which is of great importance to reveal the influence mechanism of structure on property.In this work,based on LAP and high efficiency hydrosilylation,the desired structures of SP photochromic polymers with PS homopolymer or block copolymer backbones are obtained.(1)The backbone of Si-H functionalized polystyrene(PVPDMS)is prepared by LAP.Two kinds of SP monomers with the end of Yne group,i.e.,SP-phenyl-Yne(M₁)and SP-biphenyl-Yne(M₂)are synthesized and subsequently graft into PVPDMS by hydrosilylation.PVPDMS-SPM₁ and PVPDMS-SPM₂ with PS homopolymer backbone are successfully prepared.The calculation results of ¹H-NMR show that,the addition efficiency of Si-H group in PVPDMS with Yne ended SP monomers are close to 100%at room temperature.The photoinduced solvatochromic behavior of SP monomers and responding polymers in different solvents is studied by UV-Vis spectroscopy.The results confirm that in different solvents,SP monomers and polymers rapidly undergo open-loop and closed-loop isomerization during the 365 nm UV-light switching process accompaning by the color generation and fading.Possible transition processes between different SP isomers are proposed,the correlation between photoinduced solvatochromic with solvent polarity and molecular structure is confirmed,as well as the relationship between the formation of H-aggregation and cis-MC with solvent polarity.(2)The block copolymers containing PVPDMS(M_n=4 kg/mol)and polybutadiene(PB)with different molecular weight(M_n=6 kg/mol;18 kg/mol;30 kg/mol),i.e.,PVPDMS-b-PB_6k/18k/30k are prepared through LAP,in which the content of 1,2-PBs in the PB block is about8 mol%.Taking the PVPDMS-b-PB_6k as example,SP-phenyl-Yne(M₁)is grafted into the block copolymer backbone by hydrosilylation and(PVPDMS-g-SP)-b-PB_6k is successfully prepared.The calculation results of ¹H-NMR show that at room temperature,the addition efficiency of Si-H groups in PVPDMS block with the SP monomer is close to 100%,while the 1,2-PBs and1,4-PBs in PB block can hardly react with the Si-H groups.In addition,the photoinduced solvatochromic behavior of functionalized polymer in different solvents is studied by UV-Vis spectroscopy.The results represent that(PVPDMS-g-SP)-b-PB_6k rapidly undergoes the process of coloring and fading during the switch of 365 nm UV-light,which exhibits similar photoinduced solvatochromic behavior to that of PVPDMS-SPM₁/SPM₂.The work provides foundation for further research about the effects of different PB molecular weights on photochromic and solvatochromic behavior.