Synthesis And Properties Of Polymers Grafted Silica And GO Via Surface Graft Polymerization

Inorganic-organic hybrid materials have been widely applied in electronics, optics,bio-nanotechnology, catalysis, semiconductor and other fields since they were exploited.As new inorganic non-metallic materials, silica nanoparticles and graphene oxide(GO) are good carriers for polymeric materials, and the hybrid materials obtained have been widely favored for their excellent physicochemical stability. In this study, silica/graphene oxide-polymer hybrid materials were prepared by combination of reversible addition-fragmentation chain transfer(RAFT) polymerization and coupling reactions involving quaternization reaction and epoxy-carboxyl ring-opening reaction via surface grafting processes. On this basis, the surface properties, thermal properties and dispersibility of the hybrid materials were explored. The main contents are as follows.The research in Part 1 primarily aimed at synthesis and properties of silica nanoparticles grafted with quaternized linear, comblike and toothbrushlike copolymers. As a versatile platform for postpolymerization modification, poly(N,N-dimethylaminoethyl methacrylate)(PDMA) grafted silica nanoparticles(Si O2-g-PDMA, G1) were initially prepared by tandem approach comprising simultaneous alkoxysilane-hydroxyl coupling reaction and RAFT polymerization mediated by a couplable RAFT agent 4-(trimethoxysilyl)benzyl dithiobenzoate(TBDB). On this basis, bromide-functionalized small molecules and polymers were attached onto surface-tethered PDMA backbone to form linear and comblike copolymers grafted silica via “grafting onto” method, and tandem quaternization and RAFT process using difunctional 3-bromopropyl 4-benzodithioyl-4-cyanopentanoate(BBCP) were used to generate toothbrushlike copolymers grafted silica. During synthesis of comblike and toothbrushlike copolymers grafted silica, the grafted polymers usually had controlled molecular weight and low polydispersity(PDI = 1.08-1.14). As the grafted chains had molecular weight within the range 2710-7510 g mol-1, their molar grafting ratio was estimated to be 38.3-80.4 μmol g-1. The Tg of G1 was slightly higher than the Tg of PDMA, and DLS results showed that PDMA segments had a significant increase in the hydrodynamic diameter with a shift of hydrophilic to hydrophobic at 44 o C. The surface wettability of the quaternized membrane varied within a wide range(CA(25 o C) = 21.3o ~89.1o, CA(50oC) = 30.2o~ 85.4o), and all the hybrid membranes could exhibit more or less temperature-dependent surface wettability. This study affords a straightforward and versatile method to construct quaternized macromolecular architectures grafted onto hydroxyl-rich solid substrates, and the resultant silica-polymer hybrids may have a great potential in stimuli-responsive emulsifiers, surface and antibacterial materials.The research in Part 2 aimed at synthesis and characterization of graphene oxide grafted with homopolymers, di-, tri- and tetrablock copolymers. Glycidyl 4-benzodithioyl-4-cyanopentanoate(GBCP) mediated RAFT polymerization and the subsequent chain extension polymerization afforded well-defined homopolymers, di- and triblock copolymers bearing terminal epoxy functionality. On this basis, tandem epoxy-carboxyl ring-opening reaction and RAFT polymerization were performed to give homopolymers,di-, tri- and tetrablock copolymers grafted GO, in which GBCP and macro RAFT agents acted as both coupling agent and RAFT agent. As selective hydrolysis of surface-tethered poly(tert-butyl acrylate) segments were performed, p H sensitve GO-polymer composites containing hydrophilic poly(acrylic acid)(PAA) segments were obtained. 1H NMR and GPC were used to characterize free and grafted polymers, and IR, Raman, XRD, TGA,XPS and other tests were operated to characterize the structure and properties of the resultant composites. As determined by TGA results, the weight ratio of grafted polymers to GO 66.9-172%. The weight grafting ratio and grafting density were relatively high,revealing the good compatibility between ring-opening reaction and RAFT polymerization.The dispersibility of composites in various solvents was investigated, and GO-polymer composites could exhibit lamellar, spherical and network-like morphologies as given by SEM and TEM images. When PAA-bearing composites were dispersed in an aqueous solution(p H = 10), granular and petaloid like morphologies were obtained. Therefore, an efficient method to prepare GO-polymer composites was developed in this study, and the resultant nanocomposites may have a great potential in functional membranes, modifiers and additives.In summary, linear, comblike, and toothbrushlike(co)polymers were successfully grafted onto the surface of silica nanoparticles and graphene oxide, and the structure,composition, performance of the hybrid materials were studied. Their potential applications in stimuli-responsive surface materials were explored. The study provides a new method to prepare functional inorganic-organic hybrid materials, and the facile synthesis can be conducted under mild conditions. The straightforward and versatile method can be extended to construct quaternized or linear polymers grafted onto hydroxyl-rich solid substrates, and thus it is meaningful for surface modification and functionalization of various supports.