Thermoresponsive hydrogel of poly(glycidyl methacrylate‐co‐N‐isopropylacrylamide) as a nanoreactor of gold nanoparticles

The synthesis of a thermoresponsive hydrogel of poly(glycidyl methacrylate‐co‐N‐isopropylacrylamide) (PGMA‐co‐PNIPAM) and its application as a nanoreactor of gold nanoparticles are studied. The thermoresponsive copolymer of PGMA‐co‐PNIPAM is first synthesized by the copolymerization of glycidyl methacrylate and N‐isopropylacrylamide using 2,2′‐azobis(isobutyronitrile) as an initiator in tetrahydrofuran at 70 °C and then crosslinked with diethylenetriamine to form a thermoresponsive hydrogel. The lower critical solution temperature (LCST) of the thermoresponsive hydrogel is about 50 °C. The hydrogel exists as 280‐nm spheres below the LCST. The diameter of the spherical hydrogel gradually decreases to a minimum constant of 113 nm when the temperature increases to 75 °C. The hydrogel can act as a nanoreactor of gold nanoparticles because of the coordination of nitrogen atoms of the crosslinker with gold ions, on which a hydrogel/gold nanocomposite is synthesized. The LCST of the resultant hydrogel/gold nanocomposite is similar to that of the hydrogel. The size of the resultant gold nanoparticles is about 15 nm. The hydrogel/gold nanocomposite can act as a smart and recyclable catalyst. At a temperature below the LCST, the thermoresponsive nanocomposite is a homogeneous and efficient catalyst, whereas at a temperature above the LCST, it becomes a heterogeneous one, and its catalytic activity greatly decreases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2812–2819, 2007     

Tuning the low critical solution temperature of polymer brushes grafted on single‐walled carbon nanotubes and temperature dependent loading and release properties

A nondestructive method was developed for grafting and retrieving polymer brushes from single‐walled carbon nanotubes (SWCNT)s based on mussel‐inspired chemistry. Thermo‐responsive polymer brushes were grafted on SWCNTs by coating the tubes with polydopamine as a reactive underlayer and sequential surface‐initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate (OEGMA, M_n = 475) and 2‐(2'‐methoxyethoxy)ethyl methacrylate (MEO2MA). Copolymer brushes were retrieved from the SWCNTs using 1 M NaOH to destroy the crosslinked polydopamine coating, and after that, the pristine properties of the SWCNTs were preserved. The low critical solution temperature (LCST) and molecular weight of the copolymer were measured using a nephelometer and gel permeation chromatograph, respectively. The loading and release behavior of Rhodamine 6G on responsive polymer‐grafted SWCNTs demonstrates that the copolymer brushes confer the SWCNTs an LCST dependence. This method can accurately confirm the molecular weights and polydispersity of stimuli‐responsive polymers grafted on any other nanoparticles and predict their controlled release behavior. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1807–1814     

Stimuli‐responsive diblock copolymer brushes via combination of “click chemistry” and living radical polymerization

pH‐ and temperature‐responsive poly(N‐isopropylacrylamide‐block?4‐vinylbenzoic acid) (poly(NIPAAm‐b‐VBA)) diblock copolymer brushes on silicon wafers have been successfully prepared by combining click reaction, single‐electron transfer‐living radical polymerization (SET‐LRP), and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization. Azide‐terminated poly(NIPAAm) brushes were obtained by SET‐LRP followed by reaction with sodium azide. A click reaction was utilized to exchange the azide end group of a poly(NIPAAm) brushes to form a surface‐immobilized macro‐RAFT agent, which was successfully chain extended via RAFT polymerization to produce poly(NIPAAm‐b‐VBA) brushes. The addition of sacrificial initiator and/or chain‐transfer agent permitted the formation of well‐defined diblock copolymer brushes and free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Ellipsometry, contact angle measurements, grazing angle‐Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy were used to characterize the immobilization of initiator on the silicon wafer, poly(NIPAAm) brush formation via SET‐LRP, click reaction, and poly(NIPAAm‐b‐VBA) brush formation via RAFT polymerization. The poly(NIPAAm‐b‐VBA) brushes demonstrate stimuli‐responsive behavior with respect to pH and temperature. The swollen brush thickness of poly(NIPAAm‐b‐VBA) brush increases with increasing pH, and decreases with increasing temperature. These results can provide guidance for the design of smart materials based on copolymer brushes. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2677–2685     

Novel thermo‐responsive self‐assembly micelles from a double brush‐shaped PNIPAM‐g‐(PA‐b‐PEG‐b‐PA)‐g‐PNIPAM block copolymer with PNIPAM polymers as side chains

A novel double brush‐shaped copolymer with amphiphilic polyacrylate‐b‐poly(ethylene glycol)‐b‐poly acrylate copolymer (PA‐b‐PEG‐b‐PA) as a backbone and thermosensitive poly(N‐isopropylacrylamide) (PNIPAM) long side chains at both ends of the PEG was synthesized via an atom transfer radical polymerization (ATRP) route, and the structure was confirmed by FTIR, ¹H NMR, and SEC. The thermosensitive self‐assembly behavior was examined via UV‐vis, TEM, DLS, and surface tension measurements, etc. The self‐assembled micelles, with low critical solution temperatures (LCST) of 34–38 ^°C, form irregular fusiform and/or spherical morphologies with single, double, and petaling cores in aqueous solution at room temperature, while above the LCST the micelles took on more regular and smooth spherical shapes with diameter ranges from 45 to 100 nm. The micelle exhibits high stabilities even in simulated physiological media, with low critical micellization concentration (CMC) up to 5.50, 4.89, and 5.05 mg L^?1 in aqueous solution, pH 1.4 and 7.4 PBS solutions, respectively. The TEM and DLS determination reveled that the copolymer micelle had broad size distribution below its LCST while it produces narrow and homogeneous size above the LCST. The cytotoxicity was investigated by MTT assays to elucidate the application potential of the as‐prepared block polymer brushes as drug controlled release vehicles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Homopolymer and block copolymer brushes on gold by living anionic surface‐initiated polymerization in a polar solvent

Living anionic surface‐initiated polymerization on flat gold substrates has been conducted to create uniform homopolymer and diblock copolymer brushes. A 1,1‐diphenylethylene (DPE) self‐assembled monolayer was used as the immobilized precursor initiator. n‐BuLi was used to activate the DPE in tetrahydrofuran at –78 °C to initiate the polymerization of different monomers (styrene, isoprene, ethylene oxide, and methyl methacrylate). Poly(styrene) (PS) and poly(ethylene oxide) (PEO) in particular were first investigated as grafted homopolymers, followed by their copolymers, including poly(isoprene)‐b‐poly(methylmethacrylate) (PI‐b‐PMMA). A combined approach of spectroscopic (Fourier transform infrared spectroscopy, surface plasmon spectroscopy, ellipsometry, X‐ray photoelectron spectroscopy) and microscopic (atomic force microscopy) surface analysis was used to investigate the formation of the polymer brushes in polar solvent media. The chemical nature of the outermost layer of these brushes was studied by water contact angle measurements. The effect of the experimental conditions (solvent, temperature, initiator concentration) on the surface properties of the polymer brushes was also investigated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 769–782, 2006     

Temperature‐induced phase transition of poly(N‐n‐propylacrylamide‐co‐butyl methacrylate‐co‐N,N‐diethylaminoethyl methacrylate)

Terpolymers composed of N‐n‐propylacrylamide (NPAAm), butyl methacrylate (BMA), and N,N‐diethylaminoethyl methacrylate (DEAEMA) were prepared in an attempt to investigate the temperature‐induced phase transition and its mechanism. Poly(NPAAm) showed the lower critical solution temperature (LCST) around 24°C in water. With the incorporation of DEAEMA with NPAAm, the LCST change was characterized by an initial increase. However, the LCST was shifted to the lower temperature at the later stage. This might be explained in terms of hydrophilic/hydrophobic contribution of DEAEMA to the LCST. The swelling behavior of copolymer gel in the various solvents and spin‐lattice relaxation time (T₁) study by NMR strongly suggested the hydrophilic/hydrophobic contribution of DEAEMA to the LCST depending on the local environment. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1407–1411, 1999     

Multifunctional ATRP initiators: Synthesis of four‐arm star homopolymers of methyl methacrylate and graft copolymers of polystyrene and poly(t‐butyl methacrylate)

Tetrakis bromomethyl benzene was used as a tetrafunctional initiator in the synthesis of four‐armed star polymers of methyl methacrylate via atom transfer radical polymerization (ATRP) with a CuBr/2,2 bipyridine catalytic system and benzene as a solvent. Relatively low polydispersities were achieved, and the experimental molecular weights were in agreement with the theoretical ones. A combination of 2,2,6,6‐tetramethyl piperidine‐N‐oxyl‐mediated free‐radical polymerization and ATRP was used to synthesize various graft copolymers with polystyrene backbones and poly(t‐butyl methacrylate) grafts. In this case, the backbone was produced with a 2,2,6,6‐tetramethyl piperidine‐N‐oxyl‐mediated stable free‐radical polymerization process from the copolymerization of styrene and p‐(chloromethyl) styrene. This polychloromethylated polymer was used as an ATRP multifunctional initiator for t‐butyl methacrylate polymerization, giving the desired graft copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 650–655, 2001     

A new thermo‐responsive block copolymer with tunable upper critical solution temperature and lower critical solution temperature in the alcohol/water mixture

The multi‐thermo‐responsive block copolymer of poly[2‐(2‐methoxyethoxy)ethyl methacrylate]‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PMEO₂MA‐b‐PVEA) displaying phase transition at both the lower critical solution temperature (LCST) and the upper critical solution temperature (UCST) in the alcohol/water mixture is synthesized by reversible addition‐fragmentation chain transfer polymerization. The poly[2‐(2‐methoxyethoxy)ethyl methacrylate] (PMEO₂MA) block exhibits the UCST phase transition in alcohol and the LCST phase transition in water, while the poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PVEA) block shows the UCST phase transition in isopropanol and the LCST phase transition in the alcohol/water mixture. Both the polymer molecular weight and the co‐solvent/nonsolvent exert great influence on the LCST or UCST of the block copolymer. By adjusting the solvent character including the water content and the temperature, the block copolymer undergoes multiphase transition at LCST or UCST, and various block copolymer morphologies including inverted micelles, core‐corona micelles, and corona‐collapsed micelles are prepared. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4399–4412     

Schiff base as a novel kind of catalyst for reversible complexation‐mediated radical polymerization of methyl methacrylate

Two kinds of Schiff base, N,N′‐dibenzylidene‐1,2‐diaminoethane (NDBE) and N,N′‐disalicylidene‐1,2‐diaminoethane, have been found as efficient organic catalyst for reversible complexation‐mediated radical polymerization (RCMP) of methyl methacrylate (MMA) for the first time. The polymerization results show obvious features of “living”/controlled radical polymerization. Well‐defined and low‐polydispersity polymers (M_w/M_n = 1.20–1.40) are obtained in RCMP of MMA catalyzed by Schiff base at mild temperature (65–80°C). Moreover, Schiff base also exhibits a particularly high reactivity for RCMP of MMA with in situ formed alkyl iodide initiator. The polymer molecular weight and its polydispersity (M_w/M_n is around 1.20) are well controlled even with high monomer conversion. Notably, when the dosage of azo initiator is same as the dosage of iodine, the polymerization could also be realized in the presence of NDBE. The living feature of synthesized polymer is confirmed through the chain extension experiment. In short, Schiff base is a kind of high‐efficient catalyst for RCMP and reverse RCMP of MMA, which can be one of the most powerful and robust techniques for polymer synthesis. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1653–1663     

Temperature and pH dual stimuli responsive PCL‐b‐PNIPAAm block copolymer assemblies and the cargo release studies

A new atom transfer radical polymerization (ATRP) initiator, namely, 2‐(1‐(2‐azidoethoxy)ethoxy)ethyl 2‐bromo‐2‐methylpropanoate containing both “cleavable” acetal linkage and “clickable” azido group was synthesized. Well‐defined azido‐terminated poly(N‐isopropylacrylamide)s (PNIPAAm‐N₃)s with molecular weights and dispersity in the range 11,000–19,000 g mol^?1 and 1.20–1.28, respectively, were synthesized employing the initiator by ATRP. Acetal containing PCL‐b‐PNIPAAm block copolymer was obtained by alkyne–azide click reaction of azido‐terminated PNIPAAm‐N₃ with propargyl‐terminated PCL. Critical aggregation concentration (CAC) of PCL‐b‐PNIPAAm copolymer in aqueous solution was found to be 8.99 × 10^?6 M. Lower critical solution temperature (LCST) of PCL‐b‐PNIPAAm copolymer was found to be 32 °C which was lower than that of the precursor PNIPAAm‐N₃ (36.4 °C). The effect of dual stimuli viz . temperature and pH on size and morphology of the assemblies of PCL‐b‐PNIPAAm block copolymer revealed that the copolymer below LCST assembled in spherical micelles which subsequently transformed to unstable vesicles above the LCST. Heating these assemblies above 40 °C led to the precipitation of PCL‐b‐PNIPAAm block copolymer. Whereas, at decreased pH, micelles of PCL‐b‐PNIPAAm copolymer disintegrate due to the cleavage of acetal linkage and precipitation of hydrophobic hydroxyl‐terminated PCL. The encapsulated pyrene release kinetics from the micelles of synthesized PCL‐b‐PNIPAAm copolymer was found to be faster at higher temperature and at lower pH. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1383–1396     

N‐chloro amides,lactams, carbamates,and imides. New classes of initiators for the metal‐catalyzed living radical polymerization of methacrylates

Metal‐catalyzed living radical polymerization of methyl methacrylate initiated with N‐chloro amides (N‐chloro N‐ethyl propionamide, N‐chloro benzanilide, N‐chloro methylbenzamide, and N‐chloro acetanilide), lactams (N‐chloro caprolactam and N‐chloro 2‐pyrrolidinone), carbamates or urethanes (N‐chloro ethylcarbamate or N‐chlorourethane), imides (N‐chloro phtalimide, N‐chloro succinimide, trichloroisocyanuric acid, and N‐chloro saccharin) and catalyzed with the self‐regulated catalytic system Cu₂S/2,2′‐bipyridine is reported. The initiation efficiency of these initiators is determined by their structure. Regardless of the initiator efficiency, in all cases, poly (methyl methacrylate) with narrow molecular weight distribution and functionalized chain‐ends was obtained. These new classes of initiators open new strategies for the functionalization of polymer chain‐ends and for the synthesis of complex architectures by graft copolymerization initiated from N‐chloro proteins, aliphatic, aromatic and semiaromatic polyamides, and polyurethanes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5283–5299, 2005     

Solid‐supported amphiphilic triblock copolymer membranes grafted from gold surface

Gold‐supported amphiphilic triblock copolymer brushes composed of two hydrophilic poly(2‐hydroxyethyl methacrylate) (PHEMA) blocks and a hydrophobic poly(n‐butyl methacrylate) (PBMA) middle part were synthesized using a surface‐initiated ATRP. Attenuated total reflectance Fourier transform infrared spectroscopy, polarization modulation infrared reflection absorption spectroscopy (PM‐IRRAS), ellipsometry, contact angle measurements, and atomic force microscopy were used for the characterization of PHEMA‐co‐PBMA‐co‐PHEMA brushes. The PM‐IRRAS analysis revealed an increase of the chain tilt toward the gold surface during growth of the individual blocks. We suggest that the orientation of the amphiphilic polymer brushes is influenced by both the chain length and the interchain interactions. Additionally, a detachment of the polymer membranes from the solid support and subsequent gel permeation chromatography analyses allowed us to establish their compositions. We applied block‐selective solvents (water and hexane) as well as a good solvent for the whole polymer chain (ethanol) to study the morphology and solvent responsive behavior of the amphiphilic brushes. The presented results could serve as a good starting point for the fabrication of functional solid‐supported membranes for biosensing applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1–13, 2009     

Thermosensitive and control release behavior of poly (N‐isopropylacrylamide‐co‐acrylic acid) latex particles

In this work, poly(N‐isopropylacrylamide‐co‐acrylic acid) (poly(NIPAAm‐AA)) copolymer latex particles (microgels) were synthesized by the method of soapless emulsion polymerization. Poly(NIPAAm‐AA) copolymer microgels have the property of being thermosensitive. The concentration of acrylic acid (AA) and crosslinking agent N,N′‐methylenebisacrylamide were important factors to influence the lower critical solution temperature (LCST) of poly(NIPAAm‐AA) microgels. The effects of AA and crosslinking agent on the swelling behavior of poly(NIPAAm‐AA) microgels were also studied. The poly(NIPAAm‐AA) copolymer microgels were then used as a thermosensitive drug carrier to load caffeine. The effects of concentration of AA and crosslinking agent on the control release of caffeine were investigated. How the AA content and crosslinking agent influenced the morphology and LCST of the microgels was discussed in detail. The relationship of morphology, swelling, and control release behavior of these thermosensitive microgels was established. A new scheme was proposed to interpret the control release of the microgels with different morphological structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5734–5741, 2008     

Quantification of ATRP initiator density on polymer latex particles by fluorescence labeling technique using copper‐catalyzed azide‐alkyne cycloaddition

We developed a novel fluorescence labeling technique for quantification of surface densities of atom transfer radical polymerization (ATRP) initiators on polymer particles. The cationic P(St‐CPEM‐C₄DMAEMA) and anionic P(St‐CPEM) polymer latex particles carrying ATRP‐initiating chlorine groups were prepared by emulsifier‐free emulsion polymerization of styrene (St), 2‐(2‐chloropropionyloxy)ethyl methacrylate (CPEM), and N‐n‐butyl‐N,N‐dimethyl‐N‐(2‐methacryloyloxy)ethylammonium bromide (C₄DMAEMA). ATRP initiators on the surface of polymer particles were converted into azide groups by sodium azide, followed by fluorescent labeling with 5‐(N,N‐dimethylamino)‐N′‐(prop‐2‐yn‐1‐yl)naphthalene‐1‐sulfonamide (Dansyl‐alkyne) by copper‐catalyzed azide‐alkyne cycloaddition (CuAAC). The reaction time required for both azidation of ATRP‐initiating groups and successive fluorescence labeling of azide groups with Dansyl‐alkyne by CuAAC were investigated in detail by FTIR and fluorescence spectral measurement, respectively. The ATRP initiator densities on the cationic P(St‐CPEM‐C₄DMAEMA) and anionic P(St‐CPEM) particle surfaces were estimated to be 0.21 and 0.15 molecules nm^?2, respectively, which gave close agreement with values previously determined by a conductometric titration method. The fluorescence labeling through click chemistry proposed herein is a versatile technique to quantify the surface ATRP initiator density both on anionic and cationic polymer particles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4042–4051     

Dual stimuli‐responsive polyamines derived from modified N‐vinylpyrrolidones through CuAAC click chemistry

The synthesis via copper(I)‐catalyzed azide alkyne cycloaddition (CuAAC) of three new monomer derivatives of N‐vinyl‐2‐pyrrolidone (VP) carrying cyclic pyrrolidine, piperidine, and piperazine groups and the corresponding copolymers with unmodified VP is shown. The systems bearing pyrrolidine and piperidine displayed both thermo‐ and pH‐response, which has not been reported previously for a polymer with polyvinylpyrrolidone (PVP) backbone. A broad modulation of the LCST with the copolymer composition and pH was observed in a temperature range 0–100 °C. The polymers carrying piperazine exhibited broad buffering regions and no thermosensitivity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1098–1108     

Preparation,morphology, and thermoresponsive properties of poly(N‐isopropylacrylamide)‐based copolymer microgels

In this research, thermoresponsive copolymer latex particles with an average diameter of about 200–500 nm were prepared via surfactant‐free emulsion polymerization. The thermoresponsive properties of these particles were designed by the addition of hydrophilic monomers [acrylic acid (AA) and sodium acrylate (SA)] to copolymerize with N‐isopropylacrylamide (NIPAAm). The effects of the comonomers and composition on the synthesis mechanism, kinetics, particle size, morphology, and thermoresponsive properties of the copolymer latex were also studied to determine the relationships between the synthesis conditions, the particle morphology, and the thermoresponsive properties. The results showed that the addition of hydrophilic AA or SA affected the mechanism and kinetics of polymerization. The lower critical solution temperature (LCST) of the latex copolymerized with AA rose to a higher temperature. However, because the strong hydrophilic and ionic properties of SA caused a core–shell structure, where NIPAAm was in the inner core and SA was in the outer shell, the LCST of the latex copolymerized with SA was still the same as that of pure poly(N‐isopropylacrylamide) latex. It was concluded that these submicrometer copolymer latex particles with different thermoresponsive properties could be applied in many fields. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 356–370, 2006     

Temperature‐induced aggregation of the copolymers of N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate in aqueous solutions

A series of random copolymers of N‐isopropylacrylamide (NIPAM) and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate (AMPS) was synthesized by free‐radical copolymerization. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol %. The lower critical‐solution temperature (LCST) of copolymers in water increased strongly with an increasing content of AMPS. The influence of polymer concentration on the LCST of the copolymers was studied. For the copolymers with a higher AMPS content, the LCST decreased faster with an increasing concentration than for copolymers with a low content of AMPS. For a copolymer containing 1.1 mol % of AMPS the LCST dropped by about 3 °C when the concentration increased from 1 to 10 g/L, whereas for a copolymer containing 9.6 mol % of AMPS the LCST dropped by about 10 °C in the concentration range from 2 to 10 g/L. It was observed that the ionic strength of the aqueous polymer solution very strongly influences the LCST. This effect was most visible for the copolymer with the highest content of AMPS (9.6 mol %) for which an increase in the ionic strength from 0.2 to 2.0 resulted in a decrease in the LCST by about 27 °C (from 55 to 28 °C), whereas for the copolymer containing 1.1 mol % of AMPS the LCST decreased only by about 6 °C (from 37 to 31 °C) when the ionic strength increased from 0.005 to 0.3. The reactivity ratios for the AMPS and NIPAM monomer pairs were determined using different methods. The values of r_AMPS and r_NIPAM obtained were 11.0–11.6 and 2.1–2.4, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2784–2792, 2001     

Spontaneous Cu(I)Br–PMDETA‐mediated polymerization of isobornyl methacrylate in heterogeneous aqueous medium at ambient temperature

Isobornyl methacrylate (IBMA), a bulky hydrophobic methacrylate, undergoes very fast polymerization, in bulk, with Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA)/ethyl‐2‐bromoisobutyrate system, at ambient temperature. IBMA also undergoes a spontaneous initiator‐free polymerization, at ambient temperature, with Cu(I)Br/PMDETA catalytic system in dimethyl sulfoxide–water mixtures. The rate of the polymerization is seen to increase with the water content up to 80 mol % of water. A possible intervention of air in initiation is proposed. The active Cu(0) formed by the disproportionation of Cu(I) species in aqueous medium probably plays a vital role for a possible air‐initiation of IBMA via single electron transfer‐living radical polymerization (SET‐LRP) mechanism. A high tolerance level to water under SET‐LRP conditions is demonstrated. The poly(IBMA) samples obtained exhibit low molecular weight distributions (1.1–1.3). Similar behavior was not observed with other common methacrylates such as methyl methacrylate, t‐butyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of PS and PDMAEMA mixed polymer brushes on the surface of layered silicate and their application in pickering suspension polymerization

An ammonium free radical initiator was ion exchanged onto the surface of clay layers. Polystyrene (PS) and poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) mixed polymer brushes on the surface of clay layers were prepared by in situ free radical polymerization. PS colloid particles armored by clay layers with mixed polymer brushes were prepared by Pickering suspension polymerization. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the structure and morphology of the colloid particles. Clay layers on the surface of PS colloid particles can be observed. Because of the cationic nature of the PDMAEMA brushes the colloid particles have positive zeta potentials at low pH values. X‐ray photoelectron spectroscopy (XPS) was used to analyze the surface of the colloid particles. N_1s binding energy of PDMAEMA chains on the surface of clay layers was detected by XPS. The two peaks of the N_1s binding energy indicate two different nitrogen environments on the surface of clay layers. The peak with a lower binding energy is characteristic of neutral nitrogen on PDMAEMA chains, and the peak with a higher binding energy is attributed to protonated nitrogen on PDMAEMA chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5759–5769, 2007     

Poly(2‐hydroxyethyl methacrylate‐co‐N,O‐dimethacryloylhydroxylamine) particles by dispersion polymerization

Poly(2‐hydroxyethyl methacrylate‐co‐N,O‐dimethacryloylhydroxylamine) particles were prepared by dispersion polymerization in toluene/2‐methylpropan‐1‐ol medium using cellulose acetate butyrate and dibenzoyl peroxide (BPO) as a steric stabilizer and initiator, respectively. The particle size was reduced with decreasing solvency of the reaction medium (more nuclei were generated) because the critical chain length of the precipitated oligomers decreased with an increasing toluene content, which is a poorer solvent for the polymer than 2‐methylpropan‐1‐ol. There is an optimum initiator concentration (2 wt % BPO relative to monomers) for producing low‐polydispersity particles under given conditions. Additionally, discrete spherical particles were obtained at a low monomer concentration and/or higher polymerization temperature. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1625–1632, 2002