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Silica nanoparticles (NSiO2) are modified with mixed polymer brushes derived from a block copolymer precursor, poly(methyl methacrylate)-b-poly(glycidyl methacrylate)-b-poly(tert-butyl methacrylate) with short middle segment of PGMA, through one step “grafting-onto” approach. The block polymer precursors are prepared via reversible addition–fragmentation chain transfer-based polymerization of methyl methacrylate, glycidyl methacrylate, and tert-butyl methacrylate. The grafting is achieved by the reaction of epoxy group in short PGMA segment with silanol functionality of silica. After hydrolysis of poly(tert-butyl methacrylate) segment, amphiphilic NSiO2 with “V-shaped” polymer brushes possessing exact 1:1 molar ratio of different arms were prepared. The functionalized particles self-assemble at oil/water interfaces to form stable large droplets with average diameter ranging from 0.15 ± 0.06 to 2.6 ± 0.75 mm. The amphiphilicity of the particles can be finely tuned by changing the relative lengths of poly(methyl methacrylate) and poly(methacrylic acid) segments, resulting in different assembly behavior. The method may serve as a general way to control the surface property of the particles.

Aminolysis of polystyrene and poly(methyl methacrylate) (PMMA) prepared by reversible addition−fragmentation chain transfer (RAFT) polymerization was investigated. The product of the former contains predominantly double molecular weight species by the formation of disulfide bond, whereas the latter formed coupled species which consequently cleaved to unimolecular weight species. MALDI−TOF MS (matrix-assisted laser desorption ionization time-of-flight mass spectrometry), elemental analysis and 1H NMR indicated that thiolactone terminus was formed after aminolysis of PMMA. We propose that the thiol end groups generated during the aminolysis of PMMA tend to cyclize through “backbiting” to form thiolactone structure. A similar reaction was observed in the case of poly(N, N-dimethylaminoethyl methacrylate) and poly(laury methacrylate). Despite this, the preparation of thiol-end functionalized PMMA was achieved by introducing a short block of polystyrene after the RAFT polymerization of MMA.

Thermal decomposition of dithioesters, e.g., cumyl dithiobenzoate (CDB), poly(methyl methacrylate) (PMMA) end-capped with dithioester, and 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate (EPDB), and the consequent effect on reversible addition-fragmentation chain transfer polymerization were investigated. The former two dithioesters underwent thermal decomposition at 120 °C. The thermal decomposition yielded unsaturated compound and dithiobenzoic acid, leading to some loss of living character of the polymerization, such as retarded reaction rate and broadened molecular weight distribution. Nevertheless, thermal decomposition of EPDB, a model compound for PMMA dithioester, does not yield unsaturated product despite the resemblance of the chemical structures. Thermogravimetric analysis shows that PMMA dithioesters are more thermally unstable than the other two.

A model reaction of dithioester and alkoxyamine is proposed to probe the reversible addition-fragmentation chain transfer (RAFT) process. The kinetics of the model reaction is analyzed and compared with that of pure alkoxyamine homolysis with a Monte Carlo simulation. Although the pure alkoxyamine obeys the law of persistent radical effect, the model reaction results in higher concentration of the persistent radi- cal during the main period of the reaction. However, for a very fast RAFT process or a very low addition rate constant, the time dependence of the persistent radical concen- tration is quite close to that of pure alkoxyamine. Furthermore, the cross termination between the intermediate and alkyl radicals causes a retardation effect for the model reaction when the intermediate is relatively long-lived. The Monte Carlo simulation indicates that it is feasible to measure the individual rate constants of the RAFT pro- cess, such as the rate constant of addition, with a large excess of alkoxyamine. In addi- tion, the special feature of the system with different leaving groups in the alkoxyamine and dithioester is also discussed. V C 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym

Copolymerization of styrene and acrylonitrile was carried out via reversi-ble addition-fragmentation chain transfer process (RAFT) in the presence of cumyldithiobenzoate with AIBN as initiator. Copolymerization proceeded in a controlled/‘‘living’’ fashion, and the copolymer composition depended on the feed ratio of mono-mer pairs. Block copolymers comprising styrene and acrylonitrile (SAN) segmentsand various functional blocks were synthesized through chain extension using thefirst blocks as macromolecular chain transfer agents (macroCTAs). Since the polymer-ization of both blocks proceeded through the RAFT process, the resulting blockcopolymers exhibited relatively narrow molecular weight distribution, with polydis-persity indices in the range of 1.29–1.46. Gel permeation chromatography (GPC), and 1 H NMR and FTIR measurements confirmed the successful synthesis of the function-alized block copolymers. VV C 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:2260–2269, 2006