Radical Polymerization Of St Research Articles

Catalytic aerobic radical polymerization in typical redox-non-innocent solvents as potential low-efficiency initiators

Certain complexes of some transition metal cations in the high oxidation state could oxidize some organic substrates with labile C-H moieties, leading to the corresponding cations in the lower" oxidation state and some carbon-centered radicals. The former would form oxidative complexes with molecular dioxygen to continuously oxidize organic substrates, while the latter would initiate polymerization of vinylic monomers. Such catalytic oxidation is adopted to initiate radical polymerization of methyl methacrylate (MMA) and styrene (St) with cyclohexanone (CyHO) and benzylic hydrocarbons as both the solvent and the substrate. Although, a large array of complexes could trigger the polymerization, CuII/2,2′-bipyridine complexes display a maximum turnover frequency above 200 h–1 during the catalytic aerobic radical polymerization of MMA in CyHO at 70–80 °C, but only less than 0.4% of CyHO is involved in chain formatting. CuII/ligand-catalyzed aerobic radical polymerization of St in CyHO exhibit comparable behaviors. Only CoII complexes could catalyze the aerobic radical polymerization of MMA in para-xylene and cumene at 90 °C, but only 0.1% of PX and 0.3% of cumene are involved in chain forming.

Crosslinking-induced morphology change of latex nanoparticles: A study of RAFT-mediated polymerization in aqueous dispersed media using amphiphilic double-brush copolymers as reactive surfactants

Amphiphilic double-brush copolymers (DBCs) with each graft site quantitatively carrying both a hydrophilic poly(ethylene oxide) (PEO) graft and a hydrophobic polystyrene (PSt) graft are synthesized by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening metathesis polymerization (ROMP). These DBCs are used as both surfactants and polyfunctional RAFT agents in the radical polymerization of St in aqueous dispersed media. Miniemulsions with narrowly dispersed St-based nanodroplets are readily obtained after ultrasonication of the reaction mixtures. Without the presence of crosslinker, chain-extension polymerization of St from the DBCs yields well-defined polymeric latexes with narrow size distributions. However, with the presence of divinylbenzene (DVB) as the crosslinker, vesicular polymeric nanoparticles are formed as the major product. Such crosslinking-induced change in morphology of the resulting latex nanomaterials may be ascribed to the increase of interfacial curvature in the heterophase systems during crosslinking polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3250–3259

Synthesis of Well-Defined Poly(vinyl acetate)-b-Polystyrene by Combination of ATRP and RAFT Polymerization

The synthesis of well-defined poly(vinyl acetate)-b-polystyrene (PVAc-b-PSt) by combination of atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization was described. Two difunctional compounds, S-(2-chloropropionoxyethoxycarbonylmethyl) O-ethyl xanthate (2) and S-(2-bromo-2-methylpropionoxyethoxycarbonylmethyl) O-ethyl xanthate (3), with an activated halide group and a xanthate group in the molecule were synthesized. The activated halide group was used as an ATRP initiator to initiate polymerization of St, and the xanthate group was used as a RAFT agent to mediate polymerization of VAc. Thus, 2 was first used to mediate the radical polymerization of VAc, followed by ATRP of St, while 3 was used first to initiate the ATRP of St, followed by the RAFT polymerization of VAc. Both approaches indicate that either the radical polymerization of St or that of VAc is controlled, and well-defined PVAc-b-PSt is obtained as confirmed by gel permeation chromatography and NMR measurements.

Synthesis and characterization of 6‐ and 12‐arm star polymers by nitroxide‐mediated radical polymerization of St and MA from dendritic TIPNO‐based hexafunctional and dodecafunctional macroinitiators

AbstractDendritic multifunctional macroinitiators having six and 12 TIPNO‐based alkoxyamines, TIPNO‐6 and TIPNO‐12, were synthesized and used in the living radical polymerization of styrene (St), methyl acrylate (MA), N,N‐dimethylacrylamide (DMAAm), and isoprene (IP). The polymerizations of St initiated with TIPNO‐6 gave 6‐arm star polymers with narrow polydispersities of 1.14–1.18. In the polymerizations of MA initiated with TIPNO‐6 and TIPNO‐12, the influences of added TIPNO on the polydispersity indexes (PDIs) of the resulting star polymers were first investigated, and this led to the successful formation of poly(MA) star polymers with narrow polydispersities (1.10–1.18). Moreover, the polymerizations of DMAAm and IP from TIPNO‐6 in the presence or absence of TIPNO were briefly investigated. The benzyl ether bonds of the poly(St) and poly(MA) star polymers were cleaved by treating with Me3SiI or Pd/C, and the resulting arm's parts were analyzed with SEC. The PDIs of the resulting arm parts were low (1.19–1.23), and the Mns agreed with the Mn,theor, indicating that the poly(St) and poly(MA) star polymers had well‐controlled arms. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4364–4376, 2007

Syntheses of well-defined poly(siloxane)- b-poly(styrene) and poly(norbornene)- b-poly(styrene) block copolymers using functional alkoxyamines

Functional alkoxyamines, 1-[4-(4-lithiobutoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl- N-oxyl)ethane ( 2) and 1-[4-(2-vinyloxyethoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl- N-oxyl)ethane ( 3) were prepared, and well-defined poly(hexamethylcyclotrisiloxane)- b-poly(styrene)[poly(D 3)- b-poly(St)] and poly(norbornene)- b-poly(St) [poly(NBE)- b-poly(St)] were prepared using the alkoxyamines. The first step was preparation of poly(D 3) and poly(NBE) macroinitiators, which were obtained by the ring-opening anionic polymerization of D 3 using 2 as an initiator and the ring-opening metathesis polymerization of NBE using 3 as a chain transfer. The radical polymerization of St by the poly(D 3) and poly(NBE) macroinitiators proceeded in the ‘living’ fashion to give well-defined poly(D 3)- b-poly(St) and poly(NBE)- b-poly(St) block copolymers.