Morphology Evolution Of The Nano-objects In Polymerization-Induced Self-Assembly

Polymeric nanomaterials have attracted great attention in various fields,such as drug delivery,Pickering emulsifier,and nanoreacter.Polymerization-induced self-assembly(PISA),which greatly simplifies the process of fabricating polymeric nano-objects by combination of polymerization and self-assembly in one-pot,has been demonstrated to be a powerful approach to produce various polymeric nano-objects.Morphologies of polymeric nano-objects have great influence on their properties.Structural stability of the polymeric nano-objects is another important concern,which is essential to maintain their morphology-or size-dependent performance.In situ cross-linking polymerization-induced self-assembly(PISA)is a straightforward and convenient approach to produce polymeric nano-objects with stabilized structures.However,cross-linking usually lowers the mobility of polymer chain and hence limits the morphology evolution,so fabrication of polymeric nano-objects with higher order morphologies(such as vesicle or worm-like micelles)by in situ cross-linking PISA has ever been a big challenge.In chapter 2,polymeric nano-objects with both of higher order morphologies(such as vesicles,lamella and worm-like micelles)and cross-linked structures are produced by in situ cross-linking PISA using RAFT dispersion copolymerization of 2-(diisopropylamino)ethyl methacrylate(DIPEMA)and divinyl comonomer cystaminebismethacrylamide(CBMA).Due to the slower reaction rate of cross-linker CBMA than that of the monomer DIPEMA,and the process of cross-linking is mainly delayed to the late stage of PISA after the formation of higher order morphologies.What’s more,promoted effects on morphology evolution were observed in the in situ cross-linking PISA system.Compared with conventional PISA(absence of CBMA),higher order morphologies are usually formed in most cases of in situ cross-linking PISA at the same conditions.The branched structures of the solvophobic blocks generates at the early stage of in situ cross-linking PISA,have significantly promoting effects on the morphology evolution.Cleavage of disulfide linkage in CBMA units of the core-forming blocks by glutathione(GSH)induced morphology degradation of the nano-objects,which further demonstrated the promoting effect on morphology transition of in situ cross-linking PISA.Multi-chambered vesicles were successfully prepared by RAFT polymerization-induced self-assembly using styrene(St)as monomer,ethanol/water=7/3(mass ratio)as the solvent and polyethylene glycol(PEG45-PETTC)as macro RAFT reagent.At the same time,RAFT copolymerization-induced self-assembly of styrene(St)and oligoethylene glycol methyl ether methacrylate monomers(OEGMA)were carried out to explore the effect of introducing solvophilic moiety OEGMA into the core-forming blocks on the morphology of the resulting nano-objects.Due to the strong chain rigidity of polystyrene,the introduction of a solvophilic segment into the polystyrene segment to increase the flexibility of the core-forming blocks is a reported method to promote morphology evolution.However,in the polymerization-induced self-assembly system of St and OEGMA in ethanol/water=7/3(mass ratio),the introduction of solvophilic moieties(OEGMA)resulted in the morphology degradation of the resulting nano-objects.With the increase of solvophilic moieties in the core-forming blocks,the resulting nano-objects gradually transformed from multi-chambered vesicles to unicellular vesicles and spherical micelles.Photochromic bowl-like vesicles(BV)with reversible stimuli-responsive chromism were fabricated by PISA using the functional P(4VP-co-SPMA)-CPADB as the macro RAFT agent.The fluorescence emission of SPMA dye in the resulted polymer or nanoparticles was modulated by the UV and visible light.Upon UV irradiation,the spiropyran moieties converted to the open-ring(ME form)structure,and they can turn back to the close-ring(SP form)structure by visible light irradiation.