Visible-light-induced Free-radical Polymerization Of Acrylates With Bismuth Oxide Nanoparticles As Heterogemeous Photocatalyst

Visible light-induced radical polymerization has advantages of mild reaction conditions,simple synthesis process and low cost,etc.It has become a hot topic of living free radical polymerization in the rencent years.Metal oxide semiconductor with the advantage of inexpensive and non-toxic has been widely used as visible light catalyst.To exploite metal oxide with low band gap to achieve visible light-induced living free radical polymerization is one of the most promising researches on photopolymerizaton.In this study,bismuth oxide(Bi2O3),a kind of semiconductor with low band gap(ca.2.8 eV),has been used as a visible light catalyst to explore the polymerization behavior of acrylate monomers.1.The polymerization of methyl methacrylate(MMA)with Bi2O3 in different solvents was investigated.The results showed that no polymerization occurred in the bulk polymerization of MMA with Bi2O3 as catalyst.However,polymerization of MMA could be carried out in solvents like tetrahydrofuran(THF)and N,N-dimethylformamide(DMF).With the increase of Bi2O3 concentration,the monomer conversion rate was increased at the same irradiation time.The system was also suitable for the monomers like glycidyl methacrylate(GMA),t-butyl acrylate(TBA),butyl acrylate(BA)and styrene(St).By technology of TEMPO capture free radicals,the tentative mechanism of MMA induced by Bi2O3/THF was proposed as follows:under visible light irradiation,the incident photons promote the photoexcitation of electrons on the surface of the Bi2O3 from the valence to the conductive band with generation of positive holes.Then,the positive holes induce THF to generate THF radicals which induce the polymerization of MMA subsequently.2.With a-bromophenylacetate(EBP)as initiator,the polymerization of MMA with Bi2O3/EBP in different solvents was studied.The results showed that the polymerization of MMA could be taken place in solvents like THF,DMF,dimethyl sulfoxide(DMSO)and acetonitrile.The system was also suitable for the monomers like TBA,BA and St.The addition of EBP can significantly increase the polymerization rate and decrease the average number molecular weights(Mn).With the increase of EBP concentration,the conversion rate increased at the same irradiation time.3.With the 4-cyano-4-(phenylcarbonothioylthio)-pentanoic acid(CTP)as chain transfer agent,the polymerization of MMA with Bi2O3/EBP/CTP in THF and DMSO solvents was run.In addition of CTP,Mn has a good linear relationship with conversion and the PDI of PMMA was relatively low.The polymerization demonstrated the features of living free radical polymerization.The living features of polymerizations have also been further supported by chain extension and synthesis of PMMA-b-PBnMA diblock copolymer.The results showed that Mn increased from 4400 g·mol-1(PDI=1.09)to 6600 g·mol-1(PDI=1.25)under chain extension experiment and Mn increased from 8300 g·mol-1(PDI=1.23)to 23000 g·mol-1(PDI=1.25)under MMA-b-PBnMA diblock copolymer experiment in THF.In DMSO,Mn increased from 16300 g-mol-1(PDI=1.19)to 20800 g·mol-1(PDI=1.26)under chain extension experiment and Mn increased from 8300 g·mol-1(PDI=1.23)to 42800 g·mol-1(PDI=1.30)under MMA-b-PBnMA diblock copolymer experiment.