RAFT Mediated Living Radical Polymerization: Synthesis Of Functional Block Copolymers And Application In Polymer-Functionalized Carbon

Over the last decade, reversible addition fragmentation chain transfer mediated polymerization (RAFT), one of a number of leading living radical polymerization techniques, has attracted considerable interest. It provides molecular weights predetermined by the chain transfer agent and conversion, and, more importantly, produces polymers that can be reactived for chain extension with respect to the types of monomers and the reaction conditions. Thus the RAFT process has become the most versatile controlled polymerization that enabled the design and synthesis of a wide range of macromolecules with well-defined complex polymeric architectures, compositions, low polydispersity and functionalities with relative ease. Although the mechanism of the process has not reached agreement, a constantly growing body of work had demonstrated the successful application in the development of advanced polymeric materials.Carbon nanotubes have been an area of intense research due to its potential untility in numerous areas, such as molecular wires and electronic, sensors, high-strength fibers, and field emission displays. For a number of applications, the spatial organization of carbon nanotubes in matrix is very important. Nevertheless, the problem of insolubility in solvents and processability due to strong intertube van der Walls attraction remains a severe limitation to the extensive use. The functionalizationof carbon nanotubes is a vital tool in tailoring their properties and engineering devices, and many efforts have been undertaken with respect to this functionalization.The main purpose of this work is to study the synthesis of well-defined functional polymers via the RAFT process and surface-modification of carbon nanotubes with polymers resulting from living radical polymerization. This dissertation contains the following aspects:1 Functional monomers γ-methacropropyl trimethoxylsilane (MPS), tert-butyl methacrylate (t-BMA) and glycidyl methacrylate (GMA) were polymerized by RAFT with cumyl dithiobenzoate as a chain transfer agent and AIBN as initiator. The process showed living characteristic and the functional polymers were obtained with controlled molecular weights and polymer polydispersity indices less than 1.35. Block copolymers of PMPS-b-PtBMA, PMPS-b-PGMA, PtBMA-b-PGMA and PGMA-b-PS were synthesized by the chain extension of PtBMA and PGMA macro-chain transfer agent respectively. The functional groups such as hydrolyzable trimethoxyl silyl, tert-butyl and epoxy were introduced into the block copolymers at the same time. Meanwhile, the β-cyclodextrin containing block copolymers were synthesized by reaction of amino-modified β-cyclodextrin with the epoxy group of PGMA-b-PS.2 Copolymerization of styrene and acrylonitrile was carried out via RAFT process in the presence of cumyl dithiobenzoate with AIBN as initiator. Copolymerization proceeded in a controlled/ "living" fashion, and the copolymer composition depended on the feed ratio of monomer pairs. Block copolymers comprising styrene and acrylonitrile (SAN) segments and various functional blocks were synthesized through chain extension using the first blocks as macromolecular chain transfer agents (macroCTAs). Since the polymerization of both blocks proceeded through the RAFT process, the resulting block copolymers exhibited relatively narrow molecular weight distribution, with polydispersity indices in the range of 1.29-1.46. Gel permeation chromatography (GPC), ~1HNMR and FT-IR measurements confirmed the successful synthesis of the functionalized block copolymers.3 Block copolymers PMMA-b-P(MMA-co-GMA), PtBMA-b-P(tBMA-co-GMA) and PMMA-b-P(MMA-co-GMA)-b-PtBMA containing small amount of epoxy groups in the middle or terminal part of the chain were synthesized by sequential polymerization of functional monomers using macro-chain transfer agent viaRAFT process. At one time PMMA and PtBMA were grafted onto single-walled carbon nanotubes and multi-walled carbon nanotubes by the reaction of expoxy groups in the block copolymers and carboxylic groups on the surface of tubes, resulting in the functionalized carbon nanotubes repectively PMMA-g-MWCNT-g-PtBMA and PMMA-g-SWCNT-g-PtBMA. Amphiphilic polymers grafted tubes PMMA-g-SWCNT-g-PMAA were prepared by subsequent hydrolysis of the tert-butyl group into carboxylic group. PMMA-g-SWCNT-g-PMAA self assemble at the interfaces of chloroform and water, or toluene and water.4 Multi-walled carbon nanotubes (MWCNT) were grafted with polystyrene by in situ nitroxide mediated radical polymerization in the presence of TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) functionalized MWCNT, which was synthesized by the reaction between 4-hydroxyl-TEMPO (HO-TEMPO) and carbonyl chloride groups on the MWCNT. Although the controllability of the polymerization was not high, highly soluble grafted MWCNTs were indeed obtained, indicating that the graft polymerization was efficient. The resulting polystyrene grafted MWCNTs were easily defunctionalized at room temperature using 3-chloroperoxybenzioc acid. TEM, SEM, and TGA were employed to determine the structure, morphology, and the grafting quantities of the resulting products.