Block Copolymer Micelles Prepared By Living Free Radical Dispersion Polymerzation And Morphology Adjustment

Amphiphilic block copolymer(BCPS)micro/nano-objects have attracted great attention due to their promising potential and practical applications in biomedicine,MRI,cosmetics fields.However,traditional self-assembly methodology hinders the industrial applications of block copolymers micelles or particles due to the multiple steps and highly dilute dispersion.In recent years,polymerization-induced self-assembly(PISA)has been emerged as a powerful technique for BCPs self-assembly which overcome the drawbacks of traditional self-assembly method.This article mainly explores the preparation of amphiphilic block copolymers by micelles by PISA based on reversible addition-fragmentation chain transfer(RAFT)dispersion polymerization and atom transfer radical dispersion polymerization.The main contents are listed as follows:1.Bi-functional macro-CTA agent PDMA-TTC-PDMA and mono-functional macro-CTA agent PDMA-TTC were synthesized by RAFT polymerization using two different RAFT agents,then the RAFT dispersion polymerization of styrene(St)mediated by these macro-CTAs in ethanol/water were carried out under the same conditions,and block copolymers micellar particles with different structures were prepared.It can be seen from the transmission electron micrograph that the structure of macromolecular RAFT reagents has an important influence on the morphology of the block copolymer particles:the dispersion polymerization of St mediated by PDMA-TTC-PDMA can obtain sphere,worm and vesicle nano-objects,while the dispersion polymerization mediated by PDMA-TTC under the same conditions only obtain spherical particles with a size of tens of nanometers.2.The dispersion polymerization of St mediated by PDMA-TTC-PDMA macro-CTA in ethanol/water mixture solvent was investigated systematically.The effect of solvent composition,solid content and[PDMA-TTC-PDMA]/[AIBN]molar ratio on the morphology block copolymers micelles were researched in detail.PDMA-TTC-PDMA and PDMA-TTC were used to regulate the dispersion polymerization of St,and the influence of[PDMA-TTC-PDMA]/[PDMA-TTC]molar ratio on aggregate morphology was investigated.The results show that as the ethanol content in the co-solvent gradually increased,higher order morphologies become more common,such as vesicles and hexagonally packed hollow hoops structure.It is clear that high monomer concentrations tend to form large-size vesicles and particles with special structures.At high monomer concentrations,the chance for the inter-sphere fusion is more frequent,and the excess monomers also act as co-solvent to solvate the solvophobic PS block,which could promote the adhesion of particles and further induce phase separation of the immiscible blocks,leading to the formation of higher order morphologies.At higher molar ratio of[PDMA-TTC-PDMA]/[AIBN],it tend to form vesicle micelles.Adding PDMA-TTC in PDMA-TTC-PDMA,the dispersion polymerization system of St is conducive to form large-sized particles.When[PDMA-TTC-PDMA]/[PDMA-TTC]=8:2,particles with a bicontinuous structure can be obtained.3.The RAFT dispersion polymerization of St mediated by bi-functional macro-CTA agent polyhydroxyethyl acrylate(PHEA-TTC-PHEA)in ethanol/water medium.The effect of solvent composition and solid content on the morphology block copolymers particles were researched in detail.The results indicate that as the water content of the mixed solvent increase,the polymerization rate of St were reased,and the morphologies of PHEA-b-PSt-b-PHEA copolymer micelles changes from vesicles to porous spherical micelles.At high solid content,large-sized micelle particles were obtained.4.The continuous activator regenerative atom transfer radical polymerization(ICAR ATRP)dispersion polymerization of St in ethanol was mediated by polymethoxypolyethylene glycol acrylate(PPEGA)as macroinitiator.The effects of polymerization degree of PS block and the solid content on the morphology of PPEGA-b-PSt micelle particles were investigated.The results show that more spherical and worm micelles obtained by increasing the polymerization degree of PSt.However,worm particles did not evolve into vesicle micelles after formation of worm micelles.By increasing the solid content of the system,the number of "strung" spherical micelleswere decreased,and separate spherical micelles in the system can be observed in 40 wt%soild content system.