Topological Effect Of Block Copolymer In Polymerization-induced Self-assembly And The Preparation Of Functional Nanoparticles

Compared with traditional block polymer self-assembly methods,the emergence of the polymerization-induced self-assembly(PISA)method has greatly simplified the production process of polymer nanoparticles.Meanwhile,the concentration of prepared nanoparticles is quite high(10-50%),which gives PISA a bright prospect for mass production of polymer nanoparticles.So far,the reversible addition-fragmentation chain transfer(RAFT)polymerization method is the most widely used method among the polymerization methods in PISA.By adjusting the topology of the macromolecular chain transfer agent,the amount and composition of feeding monomer,the polymerization time and other factors,it is very convenient to obtain block copolymer nanoparticles with different morphologies or functionalities via RAFT-PISA.According to the principle of RAFT polymerization,we synthesized the corresponding macromolecular chain transfer agents and used them to prepare and characterize block copolymer nanoparticles with different morphologies or functionalities by PISA method conveniently.The results of the study are as follows:1.To explore the influence of the branched topology of the hydrophilic segment in polymerization-induced self-assembly.First,macromolecular chain transfer agents(macro-CTAs)lPEG-PETTC and bPEG-PETTC with trithioester-modified end group and similar molecular weight but different topology were synthesized.Then the copolymer nanoparticles PEG-b-PBzMA/PEG-b-PS with different morphologies(micelles,worms and vesicles)were obtained by using them as macromolecular RAFT reagents in the dispersion polymerization of benzyl methacrylate(BzMA)and styrene.Compared with its linear homologue,macro-CTA with branched hydrophilic segment contributed to the formation of micron-sized giant vesicles.This phenomenon may be attributed to enlargement of molecular area(a0)and the alternation of the chain conformation generated from branched hydrophilic block,resulting in the decrease of curvature and the expansion of radius of the assemblies.The kinetic studies of the polymerization of BzMA indicated that the branched topology of the hydrophilic segment of macromolecular chain transfer agent contributed to shortening the nucleation period during PISA,which may be due to the larger molecular area of macro-CTAs with branched topologies compared to linear homologues,and thus required less monomer and shorter time to polymerize to reach the critical solvophobic block length for nucleation.In order to verify the universality of the above conclusions,bPEG-PETTC was applied to the polymerization of 2-(diisopropylamino)ethyl methacrylate(DIPEMA)monomer.Giant polymer vesicles with the size of more than 1 μm were obtained.It was proved that the morphology difference of block copolymer self-assemblies was caused by the topological structure of macro-CTA.2.Preparation of responsive near-white light-emitting nanoparticles by polymerization-induced self-assembly method.The spiropyran-based monomer SPMA with UV light responsiveness was firstly synthesized.At the same time,based on the molecular design of the pyrene group,the monomer PyAMA which could realize blue-green fluorescence light color switching was also synthesized.These two fluorescent monomers were copolymerized with benzyl methacrylate(BzMA)applying the RAFT-PISA method to conveniently prepare near-white light-emitting responsive polymer nanoparticles.Transmission electron microscopy(TEM)images showed that the PEG-b-P(BzMA-co-PyAMA-co-SPMA)copolymer nanoparticles underwent a typical morphological evolution from micelles to nanowires and vesicles as the DP of solvophoblic segment gradually increased.365 nm was not only the excitation wavelength of the fluorescence emission of pyrene monomer,but also the ring-opening wavelength of spiropyran.Since the excitation spectrum of the merocyanine overlaps with the emission spectrum of the pyrene excimer,efficient Forster resonance energy transfer(FRET)could occur between them.The fluorescence spectrum results illustrated that when the comonomer feeding ratio was BzMA:PyAMA:SPMA=94:4:2 and the degree of polymerization was 40,the polymer nanoparticles appeared as nanowires with the coordinate of fluorescence located at(0.30,0.30)at an excitation wavelength of 365 nm.When the dispersion of copolymer nanoparticles was irradiated under UV light,the near-white light emission of the diluted polymer nanoparticle suspension could be observed with the naked eye,which proved that the near-white light emission was successfully achieved.With the prolongation of irradiation time,the white light disappeared and turned into red light emission,which indicated that the emission of copolymer nanoparticles was UV-responsive.