Synthesis Of A-C Block Copolymer By RAFT Polymerization And Its Effect On The Morphology Of PS/PBA Blends

Polymer blends is an important approach to balance various properties of polymer materials and to prepare high-performance polymeric materials.Due to incompatibility of different polymers,simply blending two polymers would lead to high interfacial tension and weak interfacial adhesion between two polymer phases. Most often,it's necessary to compatibilize polymer blends.Block copolymer,random copolymers are typical compatibilizers.Traditional block copolymer(A-B block copolymer)compatibilizer is synthesized by anionic polymerization,which is expensive,and by which copolymerization is difficult to carry out.Reversible addition/fragmentation chain transfer(RAFT)is one of living/controlled radical polymerization techniques.RAFT polymerization is applicable for many monomers, under mild conditions.Besides,RAFT copolymerization is easy to achieve.In this thesis,a series of Poly(styrene-b-(styrene-co-butyl acrylate))(A-C block copolymer),Poly(styrene-co-butyl acrylate),Poly(styrene-b-butyl acrylate)(A-B block copolymer)was synthesized via RAFT(co)polymerization.They were evaluated as compatibilizers for PSt/PBA blends.It was found that only with the initiator with small decomposition rate constant and high polymerization temperature,the block copolymer with high molecule weight and small fraction of dead chains(＜0.1)could be achieved.The reason for these quite strict requirements is that the initiator concentration should be remained far below that of the conventional radical polymerization,which is limited by the very low RAFT concentration.PS,PBA,and copolymer were mixed in Brabender at 180℃.The morphology of the mixture before and after annealing(200℃,12hr)was observed.It was found that:1.Compared with random copolymer,A-C block copolymer achieved smaller size of the dispersed phase and better thermal stability of morphology;2.St fraction in C block of A-C block copolymer had a great impact on the morphology of the blendings.When St fraction is 0.25,the PSt-b-co-4,the size of the dispersed phase is smallest,even smaller than the traditional A-B block copolymer;3.The smaller molecular weight of A-C polymer,the better compatibilizing ability within the current studied ranges;4.With increase of the A-C copolymer concentrations,the size of the dispersed phase began significantly to reduce firstly,then at a higher concentration,the size tend to be a constant value.