Synthesis Of Poly(Methacrylic Acid)-b-Poly(Acrylamide-Azobenzene) Copolymers And Its Photoresponsive Behaviors

In this thesis,poly(t-butyl methacrylate)(PtBMA)and poly(t-butyl methacrylate)-b-poly-(acrylamide-azobenzene)(PtBMA-b-PAAAB)block copolymers were synthesized via reversible addition-fragmentation chain transfer(RAFT)polymerization,using t-butyl methacrylate(tBMA)and acrylamido-azobenzene(AAAB)as monomers,1-phenylethyl dithiobenzoate(PEDB)or cumyl dithiobenzoate(CDB)as a chain transfer agent.The amphiphilic block compolymer,poly(methacrylic acid)-b-poly(acrylamido-azobenzene)(PMAA-b-PAAAB)was obtained by the hydrolysis of(PtBMA-b-PAAAB)block compolymer in the presence of trifluoroacetic acid.Then,the structures and photoresponsive behavior of these polymers were characterized and tested.Firstly,PEDB and CDB were synthesized by electrophilic addition reaction of dithiobenzoic acid with styrene and a-methylstyrene,respectively,using p-toluene sulphonic acid as catalyst.The dithiobenzoic acid was obtained from the acidification of dithiobenzoic acid brominated magnesium salt by hydrochloric acid,which prepared by the reaction of carbon disulfide and Grignard reagent formed from the reaction of bromobenzene and magnesium powder under anhydrous and oxygen-free conditions.PEDB and CDB were characterized by 1H-NMR,FT-IR,and elementary analysis.The effects of dropping rate of bromobenzene and carbon disulfide,reaction temperature and time on the yield of PEDB and CDB were discussed.The results showed that the yield of dithiobenzoic acid was up to 73%by reaction respectively for 5h at 45℃ after dropping slowly bromobenzene and carbon disulfide;the yield of PEDB and CDB was up to 49.2%and 40.8%,respectively,via electrophilic addition reaction and separation by column.Secondly,PtBMA was synthesized by RAFT polymerization of tBMA,using PEDB or CDB as a chain transfer agent,AIBN as initiator,and toluene as solvent.The effects of reaction time,temperature,initiator and chain transfer agent concentration on the polymerization of tBMA were investigated.The resulting PtBMA was characterized by FT-IR,1H-NMR,and GPC.The results showed that the kinetic curves of the polymerization of tBMA reveal good linear relationships on certain ratio of[chain transfer agent]/[monomer],either PEDB or CDB,and the rate of polymerization,molecular weight and its distribution decreased with the increase of[PEDB]/[AIBN]or[CDB]/[AIBN]ratio.However,the amount of CDB was significantly less than that of PEDB with respect to tBMA,and the molecular weight distribution was much narrower.And,the control effect of CDB was significantly better than that of PEDB for the molecular weight and its distribution of PtBMA under the same conditions of[monomer]/[chain transfer agent]/[initiator]ratio,and the CDB is ideal RAFT agent for the polymerization of tBMA.Thirdly,PtBMA was synthesized by RAFT polymerization of tBMA,using CDB as a chain transfer agent,AIBN as initiator and toluene as solvent.Then,resulting PtBMA was used as a macromolecular chain transfer agent for the systhesis of PtBMA-b-PAAAB copolymer using AAAB as monomer,AIBN as initiator,and DMF as solvent by RAFT polymerization.The kinetics of RAFT polymerization of AAAB was investigated,and the resulting PtBMA-b-PAAAB was characterized by FT-IR,1H-NMR,and GPC.And,the photoresponsive behaviors of the block copolymer were determined by UV.The results showed that the kinetic curves of AAAB polymerization reveal good linear relationship,and the molecular weight distributions were narrower(PD1<1.4);Photo-induced isomerization occurs for PrBMA-b-PAAAB,and the rate of isomerization was slowly down with the increase of the molecular weight of PAAAB block.Finaly,PMAA-b-PAAAB was obtained by hydrolysis of PtBMA-b-PAAAB with trifluoroacetic acid as catalyst,and dichloromethane as solvent at room temperature.The products were characterized by FT-IR and 1H-NMR,and the photoresponsive behaviors of the products were determined by UV.The results showed that PtBMA block was almost completely hydrolyzed,and the PMAA-b-PAAAB copolymers also have good photoresponsive behavior.However,the rate of isomerization was slower and the time to reach cis-trans isomerization equilibrium was longer than PtBMA-b-PAAAB.