Chain End Functionalizations Of "Living" Polymers And Synthesis Of Functional Cyclic Polymers

To date, chemists had done a lot of work about the end-functionalization of “Living” Radical Polymerization and synthesized various functional polymers in this way. Based on these, we provide an versatile thiocarbonylthio modification approach by the utilization of Na N3 that can be suit for almost all the typical RAFT-made polymers. In this way, the thiocarbonylthio termini of various RAFT-made polymers can be convert to thiol groups. Compared to the previous work, this method seems to be more fast and efficient. Also, we have successfully synthesized the cyclic copolymers bearing furyl group by the use of ATRP and its end-functionalization. And we have got the cyclic self-healing gels by using the copolymer cross-linked with maleimide. The detailed works were summarized as the following:(1) Chain end functionalization of RAFT polymers by utilization of Na N3Firstly, typical RAFT-made polymers, including poly-(alkyl(meth)acrylate) poly(styrene), poly(vinyl acetate) and poly(butyl acrylate) were synthesized as reported. Then, the polymer dissolved in DMF was treated with excessive Na N3 without deoxygenation at room temperature. The colour of the solution also became light immediately after the addition of Na N3. Upon addition of Na N3, the molecular weight(MW) of most of the polymers quickly increased 2-fold, also the characteristic 1H NMR and UV-vis signals of the thiocarbonylthio moieties almost disappeared. These shows the reaction is very fast and efficient. To get a clear idea about the exact mechanism of the end-functionalization of thiocarbonylthio groups under Na N3, matrix-assisted laser desorption ionization time-of-flight mass spectrometry(MALDI-TOF MS) was used to analyze the resultant PBA with bimodal MWD. From the MALDI-TOF MS, two series of peaks can be found, which was agreeing with the SEC results. One series of peaks was assigned to the thiol terminated PBA stemming from the nucleophilic process. The other agreed well with the MW with the disulfide bond(–S–S–) centered polymer generated from the terminal thiol–thiol oxidation coupling reaction. Through the reduction of disulfide bond by utilization of dithiothreitol(DTT), almost all of the twofold MW reduced to its half value. These results clearly demonstrated that Na N3 can effectively convert thiocarbonylthio groups of RAFT-made polymers to thiol groups via a nucleophilic reaction. And the nascent thiol groups readily formed disulfide groups via thiol–thiol oxidation coupling reaction under open circumstance. At the same time, we have successfully modifying the thiocarbonylthio groups of various RAFT-made polymers, such as poly-(alkyl(meth)acrylate), poly(styrene), poly(vinyl acetate), so we think it is a versatile way.(2) Controlled synthesis of functional cyclic polymers based on ATRP polymersFirstly, we explored the synthesis conditions of cyclic polymers containing furyl or maleimide group. From the experimental results, we found that a side reaction would occur when the maleimide reacted with the nucleophiles. Also the glass transition temperature of the copolymer synthesized by FMA was too high. So we synthesized the monomer FA. Then the prop-2-yn-1-yl 2-bromo-2-methylpropanoate(PBMP) was used as initiator to trigger the atom transfer radical polymerization of FA and BA. After the α-alkynyl-ω-bromine linear polymer(linear-PFA-ran-PBA-Br) was obtained, the end bromine of linear polymer was transferred to azide by Na N3. Finally, the cyclic polymer was successfully obtained via Cu AAC(Cu-catalyzed azide/alkyne cycloaddition) ring closuring reaction of α-alkynyl-ω-azide linear-PFA-ran-PBA-N3. 1H NMR, SEC and FT-IR have been employed to verify the ring topological structure of the cyclic polymers. Finally, we synthesized the polymeric gels with potential selfhealing properties with bifunctional maleimide as cross linker.