| The RDRP in the presence of iodine compounds has many ascendants such as wide range of monomers and mild reaction temperature.Especially for RCMP,it shows obviously "living" characteristics,the molecular weight polydispersity index(PDI)of obtained polymer was small and number average molecular weight(Mn)of obtained polymer agreed well with theoretical Mn.However,the type of catalyst for RCMP is limited and needs further extension.In this paper,a new kind of RCMP catalyst,Schiff base was developed.The work is as follows.1.Schiff base has been used as a new kind of catalyst for RCMP of MMA.RCMP of MMA in the presence of two kinds of Schiff base,N,N’-dibenzylidene-1 and 2-diaminoethane(NDBE)and N,N’-disalicylidene-1,2-diaminoethane(NDSE),has been studied in details.Firstly,the mechanism of polymerization was proved by detection of complex of CP-I with Schiff base and radical scavenging reaction.Then,the effects of temperatue,catalyst dosages on the polymerization were studied in details.The polymerization results in the presence of Schiff base showed obvious "living" radical polymerization characteristics.When polymerization was carried out at higher temperature,the PDI of the obtained polymer was higher than those of polymer at lower temperature.With increasing of dosage of catalyst,the polymerization speed increased,more importantly,it was found that the kinetic curves with different amounts of catalysts showed a first-order kinetic relationship with time,indciating that the number of active radicals was stable during the whole polymerization.The Mn of polymer agreed with theoretical Mn in all studied amounts of catalyst and the PDI of polymer was small.When the ratio of[MMA]0:[CP-I]0:[NDBE]0=100:1:0.25 at 70 0C,reacted 5.5 hours,number average molecular weight was 6500 g/mol and its PDI was 1.25.The strcucture of polymer was studied by H1 NMR and found that the Mn calculated by H1 NMR agreed well with Mn tested by GPC,indicating that the fraction of iodine chain end was extremely high(97%).Finally the livingness of polymerization catalyzed by Schiff base was examined by chain extension reaction.2.The reverse RCMP of MMA catalyzed by two kinds of Schiff base catalysts,NDBE and NDSE,has been studied in details.The effect of the amounts of initiator on the reverse RCMP in the presence of NDBE was studied.With decreasing of amount of initiator,the PDI of obtained polymer became smaller(PDI=1.22-1.36).When the dosage of azo initiator was the same as the dosage of iodine,the polymerization could also be realized in the presence of NDBE,while the polymerization could not happen without NDBE.Through 1H NMR experiment,it was found that the initiator efficiency was around 100%in the presence of NDBE.The influnence of amounts of catalysts(NDBE and NDSE)on the polymerization showed that all these kinetics plots showed a good linearity relationship with time,indicating that the number of active species keeps constant during polymerization process in the studied range of amounts.With increasing of the amount of catalyst,the rate of polymerization increased and the induction period was shortened.Mn values of the polymer increased linearly with monomer conversion and agreed well with their corresponding theoretical ones,Meanwhile,the PDI of polymer was narrow(1.20-1.36)in the presentation of catalysts3.Visible-light-induced RCMP of MMA in the presence of Schiff base has been studied.We researched the influence of different light sources on the polymerization.It was found that mixed light-induced RCMP of MMA,the polymerization speed was faster than pure light-induced RCMP.For all different light sources,the Mn values of polymer agreed well with their corresponding theoretical ones,and PDI of polymer was small(1.25).More importantly,high-molecular-weight PMMA with low PDI was achieved by visible-light-induced RCMP in the presence of Schiff base in a relatively short period time(Mn=80300 g/mol,PDI=1.12). |
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