Study On RAFT Polymerization Induced Self-assembly With Bimacromolecular Chain Transfer Agent

Polymerization induced self-assembly(PISA)can produce particles with different morphologies and high solid content.PISA has been a hot spot in the field of polymer synthesis.Two macro chain transfer agents(macro-CTAs)co-mediated PISA has various advantages over the single macro-CTA system.Due to the interaction between two stabilizer blocks,two macroCTAs co-mediated PISA can produce nanoparticles with richer morphologies and special structure.The vesicles usually grow inward during the PISA process.The increased wall thickness and unchanged particle size limit the ability to adjust vesicle size,which is an urgent problem to be solved in the PISA.In this paper,a series of di-block copolymer mixtures were synthesized by two macro-CTA co-mediated RAFT dispersion polymerization.The obtained nano/micro particles have a surface microphase separation structure.The effects of solvent property and various polymerization factors on the size and morphology of vesicles were explored.The specific research content and results are as follows:1.Prepare particles with different morphologies by two macro-CTAs co-mediated PISA.Two macro-CTAs(PDMAEMA macro-CTA PDMS macro-CTA)regulate Bz MA polymerization in isopropanol.Bz MA monomer simultaneously conducts chain extension for two macroCTAs to obtain di-block copolymer mixture.With increase the length of the nucleation chain,the “one-pot” method prepared particles with morphologies such as sphere,worm and vesicle.These particles are based on PBz MA as the core and PDMAEMA and PDMS as the mixed corona.Because the two blocks in the mixed corona are incompatible in the solvent,surface microphase separation occurs.which provides a new simple methods.This provides a new and convenient method for the preparation of microphase separation particles with special structures.2.The adjustment of the vesicles size by two macro-CTAs co-mediated PISA.Vesicles obtained by single macro-CTA system are following “internal phase growth” mechanism.The change of vesicle size was monitored in two macro-CTAs formulation.The result shows that as the length of the nucleation block increases,the size of vesicle increases.In some systems,higher order morphological hexagonal stacked hollow hoops(HHH)can also be obtained.The reasons for the different growth mechanisms of vesicles in two macro-CTA co-mediated PISA are discussed.When the polymer composition was fixed,the vesicles obtained in the mixed solvent were generally larger than those in the pure solvent.The reason for this phenomenon is discussed.The ability to regulate the size of vesicles by two macro-CTAs co-mediated PISA is proved.3.The influence of the feeding ratio of two macro-CTAs,water additives and comonomers on the particle morphology.Increasing the content of the flexible chain transfer agent is more conducive to obtaining high-order morphology.However,due to the insufficient stability of the flexible stabilizer on the particles,when the content is too high,only spherical micelle can be obtained.The reaction was carried out in isopropanol/water(V/V,95/5)mixture.When the composition of the copolymer was fixed,the addition of water additives made the morphology of the particles only sphere with limited kinetics.PDMAEMA-CTA was modified into zwitterionic polymer.When reacted in isopropanol containing water additive,the size of sphere increased.The introduction of flexible monomer n BA increased the flexibility of the nucleation segment,and large composite micelles(LCV)were obtained in the studied system.The reason for the change of morphology caused by single factor variable were analyzed.A variety of micro/nano particles with different morphologies can be obtained in two macro-CTAs system.