共查询到20条相似文献,搜索用时 15 毫秒
1.
Anna Tsimelzon David Deamer Rebecca Braslau 《Macromolecular rapid communications》2005,26(23):1872-1877
Summary: An initiator for nitroxide mediated ‘living’ free radical polymerization was prepared with a fluorescent tag attached to the initiating alkyl radical terminus. This was used to synthesize amphiphilic poly(acrylic acid)‐block‐polystyrene diblock copolymers, which self assembled in a tetrahydrofuran/buffer solution to form structures that are visible by fluorescence.
2.
A mechanistic model is developed for high‐temperature (138 °C) styrene semibatch thermally and conventionally initiated FRP, as well as NMP with a two‐component initiating system (tert‐butyl peroxyacetate, 4‐hydroxy‐TEMPO). The model, using kinetic coefficients from literature, provides a good representation of the FRP experimental results. Implementation of a gel effect correlation to represent the change in the diffusion‐controlled termination rate coefficient with conversion improves the fit to the thermally initiated system, but is not required to represent the production of low molecular weight material ( Dalton) by conventionally initiated FRP or NMP. The low initiator efficiency found in NMP is well explained by a reaction network involving combination of free nitroxide with methyl radicals formed from initiator decomposition.
3.
Simone Steig Frauke Cornelius Andreas Heise Rutger J. I. Knoop Gijs J. M. Habraken Cor E. Koning Henning Menzel 《Macromolecular Symposia》2007,248(1):199-206
A double-headed initiator was synthesized yielding two functional groups for the initiation of the nickel mediated ring-opening polymerization of γ-benzyl-L -glutamate-N-carboxyanhydride and controlled radical polymerization of vinyl monomers via ATRP or NMP. Well-defined block copolymers combining polypeptides and synthetic polymers were obtained. 相似文献
4.
Gaël Laruelle Jeanne Franois Laurent Billon 《Macromolecular rapid communications》2004,25(21):1839-1844
Summary: Amphiphilic diblock copolymers consisting of a hydrophilic block, poly(acrylic acid), and a hydrophobic block, polystyrene, were synthesized by direct nitroxide‐mediated polymerization using the PS block as a macro‐initiator for the first time. Several techniques were used to characterize the amphiphilic block copolymers (size exclusion chromatography, NMR spectroscopy). The proposed method can lead to samples with a broad range of composition and molar mass. Preliminary studies of their self‐assembly in aqueous medium using fluorescence spectroscopy and small‐angle neutron scattering are presented.
5.
Junpei Wakamatsu Masahiro Kawasaki Per B. Zetterlund Masayoshi Okubo 《Macromolecular rapid communications》2007,28(24):2346-2353
Nitroxide‐mediated polymerizations of styrene in microemulsion have been carried out at 125 °C using the cationic surfactant tetradecyltrimethylammonium bromide and the nitroxides 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) and N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] nitroxide (SG1). TEMPO‐mediated polymerizations were extremely slow, with large particles (dn = 39–129 nm) and broad molecular weight distributions (MWDs). The origin of the broad MWDs was likely significant alkoxyamine decomposition and differing diffusion rates of monomer and low MW alkoxyamines (and nitroxide) between monomer‐swollen micelles and polymer particles. SG1‐mediated polymerizations proceeded at higher rates, resulting in nanoparticles (dn = 21–37 nm) and lower than for TEMPO.
6.
This review article describes the preparation of polymer brushes by nitroxide‐mediated radical polymerization using either the ‘grafting to’ or the ‘grafting from’ approach. The use of TEMPO as a classical initiator is intensively described. More sophisticated nitroxides are also included in the discussion. Brush formation on flat surfaces such as wafers and also on particles is reported. Finally, some applications of polymer brushes are presented.
7.
Guillaume Delaittre Maud Save Bernadette Charleux 《Macromolecular rapid communications》2007,28(15):1528-1533
Self‐stabilized nanoparticles with a temperature‐responsive poly[(N,N‐diethylacrylamide)‐co‐(N,N′‐methylenebisacrylamide)] microgel core and a covalently attached hairy shell were synthesized via a simple nitroxide‐mediated controlled free‐radical aqueous dispersion polymerization, using a poly(sodium acrylate) alkoxyamine macroinitiator. With this method, high solid content, surfactant‐free particle suspensions were prepared, with diameter ranging from 49 to 118 nm at high temperature, and able to reversibly swell with water at low temperature. The proposed method requires a limited number of reagents in a simple polymerization procedure and thus avoids many drawbacks generally encountered in the synthesis of thermally responsive microgel particles.
8.
Farnesene (Far) is a bio‐based terpene monomer that is similar in structure to commercially used dienes like butadiene and isoprene. Nitroxide‐mediated polymerization (NMP) is adept for the polymerization of dienes, but not particularly effective at controlling the polymerization of methacrylates using commercial nitroxides. In this study, Far is statistically copolymerized with a functional methacrylate, glycidyl methacrylate (GMA), by NMP using N‐succinimidyl modified commercial BlocBuilder (NHS‐BB) initiator. Reactivity ratios are determined to be r Far = 0.54 ± 0.04 and r GMA = 0.24 ± 0.02. The ability of the poly(Far‐stat‐GMA) chains to reinitiate for chain extension with styrene showed a clear shift in molecular weight and monomodal distribution. Copolymerizations using a new alkoxyamine, Dispolreg 007 (D7), is explored as it is shown to homopolymerize methacrylates, but not yet reported for statistical copolymerizations. Bimodal molecular weight distributions are observed when an equimolar ratio of Far and GMA is copolymerized with D7 due to slow decomposition of the initiator, but chain ends are active as shown by successful chain extension with styrene. Both NHS‐BB and D7 initiators are used to synthesize poly[Far‐b‐(GMA‐stat‐Far)] and poly(Far‐b‐GMA) diblock copolymers. While the NHS‐BB initiated polymer chains have lower dispersity, D7 exhibits more linear polymerization kinetics and maintains more active chain ends. 相似文献
9.
Mn(salen)Cl was applied as a low‐cost catalyst for the formation of alkoxyamines from nitroxides and substituted styrenes. These “unimolecular initiators” for nitroxide‐mediated radical polymerization (NMRP) were synthesized using 2,2,6,6‐tetramethyl‐1‐piperidine‐1‐oxyl and 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐oxyl. Functionalized alkoxyamines were obtained from 4‐vinylbenzyl chloride and 4‐vinylbenzyl alcohol. The divinyl compound 1,2‐bis(4‐vinylphenyl)ethane was converted to an alkoxyamine monomer and to bisaminooxy compounds, which can be used as “biradical initiators” for NMRP.
10.
Jian‐Zhuang Chen Kun Cui Shu‐Yuan Zhang Peng Xie Qiao‐Ling Zhao Jin Huang Li‐Ping Shi Guang‐Yu Li Zhi Ma 《Macromolecular rapid communications》2009,30(7):532-538
Well‐defined polymethylene‐block‐polystyrene (PM‐b‐PS) diblock copolymers were synthesized via a combination of living polymerization of ylides and atom transfer radical polymerization (ATRP) of styrene. A series of hydroxyl‐terminated polymethylenes (PM‐OHs) with different molecular weight and narrow molecular weight distribution were prepared using living polymerization of ylides following efficient oxidation in a quantitive functionality. Then, the macroinitiators (PM‐MIs ( = 1 900–15 000; PDI = 1.12–1.23)) transformed from PM‐OHs in ≈ 100% conversion initiated ATRPs of styrene to construct PM‐b‐PS copolymers. The GPC traces indicated the successful extension of PS segment ( of PM‐b‐PS = 5 000–41 800; PDI = 1.08–1.23). Such copolymers were characterized by 1H NMR and DSC.
11.
John W. Ma Michael F. Cunningham Kim B. McAuley Barkev Keoshkerian Michael K. Georges 《Macromolecular theory and simulations》2002,11(9):953-960
A mathematical model has been developed to describe the interfacial mass transfer of TEMPO in a nitroxide‐mediated miniemulsion polymerization (NMMP) system in the absence of chemical reactions. The model is used to examine how the diffusivity of TEMPO in the aqueous and organic droplet phases, the average droplet diameter and the nitroxide partition coefficient influences the time required for the nitroxide to reach phase equilibrium under non‐steady state conditions. Our model predicts that phase equilibrium is achieved quickly (< 1 × 10−4 s) in NMMP systems under typical polymerization conditions and even at high monomer conversions when there is significant resistance to molecular diffusion. The characteristic time for reversible radical deactivation by TEMPO was found to be more than ten times greater than the predicted equilibration times, indicating that phase equilibrium will be achieved before TEMPO has an opportunity to react with active polymer radicals. However, significantly longer equilibration times are predicted, when average droplet diameters are as large as those typically found in emulsion and suspension polymerization systems, indicating that the aqueous and organic phase concentrations of nitroxide may not always be at phase equilibrium during polymerization in these systems.
12.
Per B. Zetterlund 《Macromolecular theory and simulations》2010,19(1):11-23
Compartmentalization and nitroxide partitioning in NMP in dispersed systems have been investigated by modeling and simulations. Compartmentalization comprises the segregation effect on termination and the confined space effect on deactivation. Under certain conditions, it is possible to obtain an improvement in both control and livingness. The particle size threshold for compartmentalization, decreases with any system change that leads to a decrease in the number of propagating radicals and/or nitroxides per particle, and vice versa. There is direct competition between the confined space effect on deactivation and nitroxide exit–the more water‐soluble the nitroxide, the weaker the confined space effect. Nitroxide partitioning leads to an increase in polymerization rate and loss in control/livingness.
13.
Xiangyang Song Qiong Ma Zhengguo Cai Ryo Tanaka Takeshi Shiono Robert B. Grubbs 《Macromolecular rapid communications》2016,37(3):227-231
Ethylene–propylene–methyl methacrylate (MMA) and ethylene–hexene–MMA A‐B‐C block copolymers with high molecular weight (>100 000) are synthesized using fluorenylamide‐ligated titanium complex activated by modified methylaluminoxane and 2,6‐di‐tert‐butyl‐4‐methylphenol for the first time. After diblock copolymerization of olefin is conducted completely, MMA is added and activated by aluminum Lewis acid to promote anionic polymerization. The length of polyolefin and poly (methyl methacrylate) (PMMA) is controllable precisely by the change of the additive amount of olefin and polymerization time, respectively. A soft amorphous polypropylene or polyhexene segment is located between two hard segments of semicrystalline polyethylene and glassy PMMA blocks.
14.
Thomas E. Enright Michael F. Cunningham Barkev Keoshkerian 《Macromolecular rapid communications》2005,26(4):221-225
Summary: Nitroxide‐mediated polymerization of styrene in a continuous tubular reactor has been demonstrated for the first time. The polymerization kinetics in the tubular reactor are similar to those in a batch reactor. The number average molecular weight increases linearly with conversion, and chain extension experiments were successful, indicating that the living nature of the polymerization is maintained in the tubular reactor.
15.
Julia Ryan Fawaz Aldabbagh Per B. Zetterlund Bunichiro Yamada 《Macromolecular rapid communications》2004,25(9):930-934
Summary: The controlled/living radical polymerizations of methyl acrylate in 50% v/v of an ionic liquid initiated by the alkoxyamine generated in situ from 4‐oxo‐2,2,6,6‐tetramethyl‐1‐piperidinyl‐N‐oxyl (4‐oxo‐TEMPO) and 2,2′‐azoisobutyronitrile (AIBN) at 140–155 °C are reported. The number‐average molecular weights increased linearly with conversion, and polydispersity indices are approximately 1.4 in the best case. The rates of polymerization were greater than in anisole, and similar to the rate of spontaneous polymerization in the ionic liquid.
16.
Tao Wu Ying Mei Chang Xu H. C. Michelle Byrd Kathryn L. Beers 《Macromolecular rapid communications》2005,26(13):1037-1042
Summary: Block copolymers of poly(ethylene oxide‐block‐2‐hydroxypropyl methacrylate) (PEO‐b‐PHPMA) with a range of molecular masses of the PHPMA block were obtained by controlled radical polymerization on a chip (CRP chip) using a PEO macroinitiator. A series of well‐controlled polymerizations were carried out at different pumping rates or reaction times with a constant ratio of monomer to initiator. The stoichiometry of the reactants was also adjusted by varying relative flow rates to change the reactant concentrations.
17.
A new synthetic approach for the preparation of block copolymers by mechanistic transformation from atom transfer radical polymerization (ATRP) to visible light‐induced free radical promoted cationic polymerization is described. A series of halide end‐functionalized polystyrenes with different molecular weights synthesized by ATRP were utilized as macro‐coinitiators in dimanganese decacarbonyl [Mn2(CO)10] mediated free radical promoted cationic photopolymerization of cyclohexene oxide or isobutyl vinyl ether. Precursor polymers and corresponding block copolymers were characterized by spectral, chromatographic, and thermal analyses. 相似文献
18.
Catherine Lefay Joël Belleney Bernadette Charleux Olivier Guerret Stphanie Magnet 《Macromolecular rapid communications》2004,25(13):1215-1220
Summary: A low‐molar‐mass poly(acrylic acid) with a narrow molar‐mass distribution, prepared by SG1 nitroxide‐mediated controlled free‐radical polymerization, was subjected to end‐group analysis to confirm its living nature. 1H and 31P NMR spectroscopy confirmed the presence of the SG1‐based alkoxyamine end group. Furthermore, chain extension with styrene and n‐butyl acrylate demonstrated the ability of the homopolymer to initiate the polymerization of a second block. These results open the door to the synthesis of poly(acrylic acid)‐based block copolymers by direct nitroxide‐mediated polymerization of acrylic acid.
19.
Akihiro Yokoyama Tomohiro Masukawa Yuka Yamazaki Tsutomu Yokozawa 《Macromolecular rapid communications》2009,30(1):24-28
Well‐defined diblock condensation copolymers composed of an aromatic polyamide and an aromatic polyether have been synthesized by means of successive chain‐growth condensation polymerizations. Polymerization of a polyamide monomer with an orthogonally difunctional initiator is accompanied with side reactions. On the other hand, polymerization with a monofunctional initiator afforded well‐defined polyamide, which has been converted into a macroinitiator by introduction of a terminal 4‐fluorobenzophenone unit. Well‐defined diblock copolymers are obtained by polymerization of a polyether monomer in the presence of this macroinitiator.
20.
Summary: Simulations based on the kinetics and mechanism of nitroxide‐mediated free radical polymerization (NMP) have been carried out in order to understand the hitherto largely unexplained effects (or lack thereof) of nitroxide partitioning in aqueous miniemulsion NMP. The focus has been on the miniemulsion NMP of styrene mediated by TEMPO and 4‐hydroxy‐TEMPO, two nitroxides with very similar activation‐deactivation equilibria, but very different organic phase‐aqueous phase partition coefficients. The general conclusion is that the organic phase propagating radical and nitroxide concentrations are unaffected by the partition coefficient in the stationary state, but the rate of polymerization and the extent of bimolecular termination increase with increasing nitroxide water solubility in the pre‐stationary state region. Specific NMP systems are, therefore, affected differently by nitroxide partitioning depending on whether polymerization predominantly occurs in the stationary state or not, which in turn is governed mainly by the activation‐deactivation equilibrium constant and the rate of thermal initiation.