Application Of Gold Nanopartciles And Semiconductor Composites In Controlled/"Living" Radical Polymerization

Photo-induced living polymerization which combines photochemistry and reversible deactivation radical polymerization（RDRP）has attracted more and more attention.Photochemistry which is usually conducted under optical irradiation and mild conditions,could show great potential in green and sustainable chemical production with spatio-temporal control.RDRP displays the advantage of producing well-defined polymers with predictable chain lengths,low dispersity,and living chain growth,which could meet the tailored requirement.At present,there have been many reports about semiconductor as photocatalyst for photomediated living polymerization.The commonly used semiconductor materials are graphite phase carbon nitride（g-C₃N₄）and cadmium sulfide（CdS）,which have the advantages of simple preparation process,wide application and visible light response.Moreover,the narrow band gap allows the generation of photocarriers with high chemical activity under visible light.Besides,the short lifetime of photogenerated carriers and the high recombination rate of electron-hole pairs lead to the limited photocatalytic efficiency.Thus,the enhancement on visible-light photoelectric（PE）response of is the key for high-efficient living polymerization with good control.Under visible-light,the localized surface plasmon resonance（LSPR）of Au or Ag nanoparticles（NPs）would lead to intense local electromagnetic field.The schottky barrier generated at the interface between metal and semiconductor could prevent the recombination of photogenerated electrons and holes and promote carrier separation.Our work has reported that Au NPs alone,could catalyze PET-RAFT polymerization under visible or near-infrared light.The alternative solution towards such problem was the combination of Au NPs and semiconductors to form heterojunction-based photocatalysts.This paper was mainly used that dual enhancement on carrier generation and migration of heterostructured photocatalysts was acheived to facilitate the efficiency of broadband RDRP polymerization,the details were listed as follows:（1）Through facile deposition-precipitation method,Au/g-C₃N₄ composites with different loading of Au NPs（1,6,10 and 13 wt%）were prepared.The effects of irradiation wavelengths on the polymerization kinetics of PET-RAFT were investigated in the range of 460-740 nm.Taking the advantage of LSPR enhancement on carrier generation,the photocatalytic activity of Au/g-C₃N₄ to PET-RAFT polymerization obviously outperformed Au NPs,g-C₃N₄ and their physical blending.Furthermore,the effect of Au content,hole scavenger,chain transfer agent（CTA）,monomer structure and polarity of solvent on polymerization were studied,demonstrating Au/g-C₃N₄ as universal and promising photocatalysts for high-efficient broadband PET-RAFT polymerization.The controlled/"living",chain end fidelity and spatio-temporal control were verified of PET-RAFT polymerization.（2）A series of Au@CdS core-shell composite photocatalysts were prepared by hydrothermal method.The RAFT polymerization behavior induced under visible light irradiation was investigated,and the living characteristics of the polymerization method were verified.In addition,the polymerization effect of RAFT polymerization using water as a more environmentally friendly and safe solvent were also explored,which exhibited the versatility of Au@CdS photocatalyst.The high chain end activity of the polymer was proved by chain extension experiments,and spatio-temporal control of the polymerization was verified by turning the"ON"or"OFF"of light source.（3）Au@CdS core-shell composite photocatalyst and ppm copper salt were used to catalyze aqueous ATRP.The polymerization results showed that the aqueous polymerization system had faster rate under visible light,and the kinetic study verified the well-controlled polymerizations.At the same time,the end of the polymer chain had high activity and could be reactivated under visible light as a macromolecular initiator to continue to initiate polymerization of other monomers,and then used for the secondary modification process of hydrogel.The rapid polymerization system provided the possibility for the subsequent rapid preparation of hydrogels and 3D printing.