| The properties of polymer materials are closely related to their structure.The synthesis of functional polymers with different specific functional monomers is the main way to optimize the properties of polymer materials.In addition,synthesis of sequence-controlled polymers is also an important development direction of functional monomers in polymer synthesis.For functionalized polymers,not only the types of functional groups,but also the order its arrangement in chain,i.e.the sequence structure,plays a very important role.Living anionic polymerization(LAP)can achieve precise control of molecular weight,molecular weight distribution and topological structure of polymers.The application of functional monomers in living anionic polymerization has also formed mature methodologies.A sequence-controlled polymer synthesis method based on living anionic polymerization has also been established by using the polymerization characteristics of functionalized 1,1-diphenylethylene(DPE)derivatives.Through the structural design of DPE derivatives,the precise regulation of the sequence structure of copolymers can be achieved by regulating the monomer reactivity.Because it is very difficult for DPE units to insert into polymer chains when dienes used as comonomers,there is a problem that type of copolymers in the sequence control method based on DPE derivatives is single and insufficient.Based on the research reports,the intramolecular bridging ring structure and the introduction of heteroatoms have a significant impact on the polymerization properties of functional monomers.Therefore,a new DPE derivative,9-methylene-9H-thiophene(MTAE),was designed and synthesized in this paper.Its two benzene rings were connected by a sulfur atom to form a triad ring structure.Its characteristics in living anionic polymerization were studied.MTAE was copolymerized with St,1,4-divinylbenzene(DVB)and isoprene(Ip)in turn with benzene as solvent and sec-butyl lithium as initiator.The results showed that MTAE had unique polymerization characteristics.The main results were as follows:1.MTAE can not copolymerize with styrene(St)at room temperature and in hydrocarbon solvents,but can copolymerize with 1,4-divinylbenzene(DVB)to form linear alternating copolymers.In addition,MTAE showed high reactivity when copolymerized with isoprene(Ip)under the same conditions,and the reactivity ratio of Ip was 0.28.Two-dimensional nuclear magnetic resonance(2D NMR)characterization showed that there is a high trans-1,4 content in the copolymer of MTAE and Ip,with trans-1,4% reaching 76%.2.In situ 1H-NMR method was used to monitor the copolymerization of MTAE and Ip(MTAE/Ip=1/2).The copolymerization kinetics was studied and the sequence structure of the copolymer was analyzed.The copolymer structure was diblock of the homopolyisoprene block and MTAE-alt-Ip block under the condition of MTAE/Ip=1/2.The control mechanism of MTAE on the stereostructure of Ip during chain growth was simulated by DFT method.It was found that the bridge structured sulfur atom in the MTAE unit at the secondary end of the living center interacted strongly with the counter ion Li at the end of Ip,thus Ip unit showed mainly trans-structure after another MTAE was added.Based on the structural design of functional monomers,this discovery provides a new idea for sequence regulation and stereostructure control of dienes in anionic polymerization. |
