Synthesis And Properties Of Solid Supports Grafted With V-Shaped And Mixed Copolymer Brushes

For solid supports such as silica particles, magnetic iron oxide, graphene oxide (GO) and synthetic resins, the surface modification with polymeric chains to form functional hybrid or composite materials have recently attracted much attention due to their variable properties and potential applications in many fields. This research was aimed at surface modification and properties of copolymer grafted silica particles and graphene oxide by combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and highly efficient coupling reactions. A series of hybrid materials and nanocomposites were efficiently synthesized, their structure and properties were characterized, and their potential applications in membrane materials and template material for biomineralization were explored. The main contents and results were listed as follows.The research in part1was focused on synthesis and properties of GO grafted with well-defined V-shaped copolymers. The target nanocomposites were obtained via combination of RAFT process and coupling reactions involving hydroxyl-alkoxysilane and carboxyl-epoxy linking reactions, and their dispersion properties, surface morphology and amphiphilic properties of complex membrane were investigated. First, functional triblock copolymers were synthesized by two-step RAFT process:(a) Monomethoxy polyethylene glycol (MPEG)-based macro chain transfer agent MPEG-CPDB (A) was used to mediate RAFT polymerization of reactive monomers such as3-(trimethoxysilyl)propyl methacrylate (MPS), tert-butyl acrylate (tBA) and glycidyl methacrylate (GMA) to synthesize MPEG-b-PM1diblock copolymers (AB) with short PM1block;(b) Chain extension polymerization of vinyl monomers such as poly(ethylene glycol) methyl ether methacrylate (PEGMA, Mn=300), styrene (St),N-isopropyl acrylamide (NIPAM), N,N-dimethyl acrylamide (DMA) and methyl acrylate (MA) was performed to prepare the target MPEG-b-PM1-b-PM2triblock copolymers (ABC). All these block copolymers possessed predetermined molecular weight, low polydispersity (PDI=1.04-1.19) and precise chemical structures, evident from GPC and1H NMR analyses. On the basis, the prefabricated reactive triblock copolymers (Mn=6510-18700g/mol) were further grafted onto GO surface by coupling reactions, and GO-V-shaped nanocomposites with molar grafting ratio in the range of0.081-0.531mmol/g were obtained. The resultant composites were characterized by IR, Raman, XPS, TGA, SEM and TEM. The results indicated the composites were of amphiphilicity since they could be efficiently dispersed in various solvents involving toluene and water and stood for a period of time up to months. The composites usually exhibited distinct aggregation behaviors in solvents, and surface morphologies such as nanoparticles, nanosheets and nanotubes (or nanorods) were observed in SEM images. The composite films had water contact angles ranging between19.4°and96.6°, and the amphiphilic properties of composite films with PNIPAM grafted chains were strongly dependent on temperature. Our preliminary results revealed the surface properties of complex films may be affected by some factors such as molecular weight and chemical composition of grafted polymers, grafting density and temperature.The research in part2was aimed at synthesis and properties of silica particles grafted with copolymers brushes with different sequences or compositions. R-functionalized S-4-(trimethoxysilyl)benzyl S’-propyltrithiocarbonate (TBPT) and Z-functionalized S-benzyl S’-trimethoxysilylpropyltrithiocarbonate (BTPT) and S-methoxycarbonyl phenylmethyl,S’-3-trimethoxysilylpropyltrithio carbonate (MPTT) were synthesized and used for synthesis of alkoxysilane-terminated homopolymers, di-and triblock copolymers with predetermined molecular weight and low polydispersity. On this basis, two types of methods, namely, direct coupling approach and tandem coupling and RAFT process were applied for fabrication of silica particles grafted with mixed polymer brushes. Silica supports were mesoporous silica particles with pore size of6.9、11.5and15.2nm and silica nanoparticles with diameter of20nm, and polymer chains were covalently grafted onto particle surface according to AB/BA and B/BA sequences. The resultant silica-copolymer hybrids were characterized by TGA, elemental analysis and IR. Aminolysis and etching were used to de-graft the grafted chains, and the weight grafting ratios and grafting densities of two kinds of grafted chains were obtained. Mixed SiO2-g-(PSt-b-PAA) hybrids were prepared by hydrolysis of SiO2-g-(PSt-b-PtBA), and their surface charge density, aggregate morphology and size were significantly depended on pH values of aqueous solution. Moreover, they had a potential as templates to induce the crystallization of NaCl and CaCO3at different conditions, and some crystalline forms such as calcite, flowerlike, laminated slate and aragonite were noted in SEM images.In summary, highly efficient approaches to synthesis of GO-copolymer nanocomposites and silica particles grafted with mixed polymer brushes were developed, well-defined V-shaped copolymers were successfully grafted onto GO surface via coupling reaction, and the advantages of R-group and Z-group methods were combined to prepare silica particles grafted with mixed copolymer brushes. The progress of this study further promotes the development of synthesis of novel hybrid and composite materials, and some approaches to facile synthesis of inorganic-polymer hybrid materials and graphene oxide-polymer nanocomposites were proposed. Therefore, this study is meaningful and valuable from viewpoints of preparation, properties and potential applications of functional hybrid and composite materials.