Synthesis of poly(chloromethylstyrene‐b‐styrene) block copolymers by controlled free‐radical polymerization

The controlled free‐radical polymerization of styrene and chloromethylstyrene monomers in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxyl (TEMPO) has been studied with the aim of synthesizing block copolymers with well‐defined structures. First, TEMPO‐capped poly(chloromethylstyrene) was prepared. Among several initiating systems [self‐initiation, dicumyl peroxide, and 2,2′‐azobis(isobutyronitrile)], the last offered the best compromise for obtaining a good control of the polymerization and a fast polymerization rate. The rate of the TEMPO‐mediated polymerization of chloromethylstyrene was independent of the initial concentration of TEMPO but unexpectedly higher than the rate of the thermal self‐initiated polymerization of chloromethylstyrene. Transfer reactions to the chloromethyl groups were thought to play an important role in the polymerization kinetics and the polydispersity index of the resulting poly(chloromethylstyrene). Second, this first block was used as a macroinitiator in the polymerization of styrene to obtain the desired poly(chloromethylstyrene‐b‐styrene) block copolymer. The kinetic modeling of the block copolymerization was in good agreement with experimental data. The block copolymers obtained in this work exhibited a low polydispersity index (weight‐average molecular weight/number‐average molecular weight < 1.5) and could be chemically modified with nucleophilic substitution reactions on the benzylic site, opening the way to a great variety of architectures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3845–3854, 2000     

Multistep and semibatch nitroxide‐mediated controlled free‐radical emulsion polymerization: A significant step toward conceivable industrial processes

Nitroxide‐mediated emulsion polymerizations of n‐butyl acrylate and styrene were performed with a monofunctional, water‐soluble alkoxyamine initiator and a difunctional one. Two different processes were applied, either in two steps or under semibatch conditions. In particular, the polymerization times were strongly reduced, while high conversions and good control over the polymer characteristics were maintained. In all cases, stable latexes were recovered; with the difunctional initiator in particular, they exhibited small particles and narrow particle size distributions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4142–4153, 2006     

Emulsion polymerization of vinyl acetate using iodine‐transfer and RAFT radical polymerizations

This study deals with control of the molecular weight and molecular weight distribution of poly(vinyl acetate) by iodine‐transfer radical polymerization and reversible addition‐fragmentation transfer (RAFT) emulsion polymerizations as the first example. Emulsion polymerization using ethyl iodoacetate as the chain transfer agent more closely approximated the theoretical molecular weights than did the free radical polymerization. Although ¹H NMR spectra indicated that the peaks of α‐ and ω‐terminal groups were observed, the molecular weight distributions show a relatively broad range (M_w/M_n = 2.2–4.0). On the other hand, RAFT polymerizations revealed that the dithiocarbamate 7 is an excellent candidate to control the polymer molecular weight (M_n = 9.1 × 10³, M_w/M_n = 1.48), more so than xanthate 1 (M_n = 10.0 × 10³, M_w/M_n = 1.89) under same condition, with accompanied stable emulsions produced. In the M_n versus conversion plot, M_n increased linearly as a function of conversion. We also performed seed‐emulsion polymerization using poly(nonamethylene L ‐tartrate) as the chiral polyester seed to fabricate emulsions with core‐shell structures. The control of polymer molecular weight and emulsion stability, as well as stereoregularity, is also discussed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and characterization of well‐defined ABC‐type triblock copolymers via atom transfer radical polymerization and stable free‐radical polymerization

An asymmetric difunctional initiator 2‐phenyl‐2‐[(2,2,6,6 tetramethylpiperidino)oxy] ethyl 2‐bromo propanoate ( 1 ) was used for the synthesis of ABC‐type methyl methacrylate (MMA)‐tert‐butylacrylate (tBA)‐styrene (St) triblock copolymers via a combination of atom transfer radical polymerization (ATRP) and stable free‐radical polymerization (SFRP). The ATRP‐ATRP‐SFRP or SFRP‐ATRP‐ATRP route led to ABC‐type triblock copolymers with controlled molecular weight and moderate polydispersity (M_w/M_n < 1.35). The block copolymers were characterized by gel permeation chromatography and ¹H NMR. The retaining chain‐end functionality and the applying halide exchange afforded high blocking efficiency as well as maintained control over entire routes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2025–2032, 2002     

First solvent‐free synthesis of poly(N‐methylolacrylamide) via frontal free‐radical polymerization

We report the first synthesis of poly (N‐methylolacrylamide) (PNMA) via free‐radical frontal polymerization (FP) with solid monomers at ambient pressure. The appropriate amounts of reactants (N‐methylolacrylamide) (NMA) and initiator (ammonium persulfate) were mixed together at ambient temperature without solvent. FP was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self‐propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. To suppress the fingers of molten monomer, a small amount of nanosilica was added. We also produced PNMA with dimethyl sulfoxide (DMSO) or N‐methyl‐2‐pyrrolidone, as solvent by FP, to study the macrokinetics in FP of PNMA without fillers. The front velocity and front temperature dependence on the ammonium persulfate and N‐methyl‐2‐pyrrolidone concentration were investigated. The polymer was analyzed by thermogravimetric analysis. Results show that without postpolymerization solvent removal, waste production can be reduced. Solvent‐free FP could be exploited as a means for preparation of PNMA with the potential advantage of higher throughput than solvent‐based methods. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4322–4330, 2007     

Star‐branched polystyrenes by nitroxide living free‐radical polymerization

Star‐branched polystyrenes, with polydispersity indices of 1.15–1.56 and 4–644 equal arms, were synthesized by the reaction of 2,2,6,6‐tetramethylpiperidin‐1‐yloxy (TEMPO)‐capped polystyrene (PS‐T) with divinylbenzene (DVB). The characterization of PS‐T and the final star polymers was carried out by size exclusion chromatography, low‐angle laser light scattering, and viscometry. The degree of branching of the star polymers depended on the DVB/PS‐T ratio and the PS‐T molecular weight. An asymmetric (or miktoarm) star homopolymer of the PS_nPS′_n type was made by the reaction of the PS_n symmetric star, which had n TEMPO molecules on its nucleus and consisted of a multifunctional initiator, with extra styrene. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 320–325, 2001     

Acrylonitrile‐containing polymers via a combination of metal‐catalyzed living radical and nitroxide‐mediated free‐radical polymerization routes

2‐Phenyl‐2‐[(2,2,6,6‐tetramethylpiperidino)oxy] ethyl 2‐bromopropanoate was successfully used as an initiator in consecutive living radical polymerization routes, such as metal‐catalyzed living radical polymerization and nitroxide‐mediated free‐radical polymerization, to produce various types of acrylonitrile‐containing polymers, such as styrene–acrylonitrile, polystyrene‐b‐styrene–acrylonitrile, polystyrene‐b‐poly(n‐butyl acrylate)‐b‐polyacrylonitrile, and polystyrene‐b‐polyacrylonitrile. The kinetic data were obtained for the metal‐catalyzed living radical polymerization of styrene–acrylonitrile. All the obtained polymers were characterized with ¹H NMR, gel permeation chromatography, and differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3374–3381, 2006     

Continuous flow synthesis of poly(methyl methacrylate) via a light‐mediated controlled radical polymerization

Controlled radical polymerizations have significantly impacted the field of polymer science by facilitating the synthesis of polymers with greater control over molecular weight, structure, and dispersity (Ð). As these synthetic techniques continue to evolve, more degrees of control can be realized via external regulation. Recent work has demonstrated external regulation of a controlled radical polymerization process with light using a photoredox Ir‐catalyst. While light offers many advantages as a stimulus for polymerization, scaling up presents unique challenges such as shallow and uneven penetration of light through the reaction medium, which negatively impacts the rate of polymerization. This work addresses some of the challenges associated with scaling up light‐mediated controlled radical polymerizations by employing a continuous flow microreactor and selecting appropriate reactor materials for oxygen sensitive reactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2693–2698     

Physically controlled,free‐radical polymerization of vaporized fluoromonomer on solid surfaces

Gas/vapor‐deposition polymerization (GDP) of vinyl monomer is expected to exhibit a unique polymerization behavior different from its polymerization in the liquid phase. Free‐radical GDP of 2,2,3,3,3‐pentafluoropropyl methacrylate (FMA) was carried out with a conventional free‐radical initiator (azobisisobutyronitrile) on substrate surfaces. A linear relationship between the number‐average molecular weight and polymer yield was observed, and the consecutive copolymerization of methyl methacrylate (MMA) and FMA led to the formation of block copolymer P(MMA‐block‐FMA). These results suggested that the GDP process on substrate surfaces has a living nature. During the process, the active species at growing chain ends may be immobilized on the deposit surface and restricted from the chain‐transfer reactions, resulting in a continuation of the propagation reaction. The GDP on substrate surfaces is therefore a physically controlled polymerization process. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2621–2630, 2004     

Synthesis of miktoarm star and miktoarm star block copolymers via a combination of atom transfer radical polymerization and stable free‐radical polymerization

A trifunctional initiator, 2‐phenyl‐2‐[(2,2,6,6‐tetramethyl)‐1‐piperidinyloxy] ethyl 2,2‐bis[methyl(2‐bromopropionato)] propionate, was synthesized and used for the synthesis of miktoarm star AB₂ and miktoarm star block AB₂C₂ copolymers via a combination of stable free‐radical polymerization (SFRP) and atom transfer radical polymerization (ATRP) in a two‐step or three‐step reaction sequence, respectively. In the first step, a polystyrene (PSt) macroinitiator with dual ω‐bromo functionality was obtained by SFRP of styrene (St) in bulk at 125 °C. Next, this PSt precursor was used as a macroinitiator for ATRP of tert‐butyl acrylate (tBA) in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 80 °C, affording miktoarm star (PSt)(PtBA)₂ [where PtBA is poly(tert‐butyl acrylate)]. In the third step, the obtained St(tBA)₂ macroinitiator with two terminal bromine groups was further polymerized with methyl methacrylate by ATRP, and this resulted in (PSt)(PtBA)₂(PMMA)₂‐type miktoarm star block copolymer [where PMMA is poly(methyl methacrylate)] with a controlled molecular weight and a moderate polydispersity (weight‐average molecular weight/number‐average molecular weight < 1.38). All polymers were characterized by gel permeation chromatography and ¹H NMR. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2542–2548, 2003     

Polymerization of styrene in alcohol/water mediated by a macro‐RAFT agent of poly(N‐isopropylacrylamide) trithiocarbonate: From homogeneous to heterogeneous RAFT polymerization

The reversible addition fragmentation chain transfer (RAFT) polymerization of styrene in alcohol/water mixture mediated with the poly(N‐isopropylacrylamide) trithiocarbonate macro‐RAFT agent (PNIPAM‐TTC) is studied and compared with the general RAFT dispersion polymerization in the presence of a small molecular RAFT agent. Both the homogeneous/quasi‐homogeneous polymerization before particle nucleation and the heterogeneous polymerization after particle nucleation are involved in the PNIPAM‐TTC‐mediated RAFT polymerization, and the two‐stage increase in the molecular weight (M_n) and nanoparticle size of the synthesized block copolymer is found. In the initial homogeneous/quasi‐homogeneous polymerization, the M_n and nanoparticle size slowly increase with monomer conversion, whereas the M_n and particle size quickly increase in the subsequent heterogeneous RAFT polymerization, which is much different from those in the general RAFT dispersion polymerization. Besides, the PNIPAM‐TTC‐mediated RAFT polymerization runs much faster than the general RAFT dispersion polymerization. This study is anticipated to be helpful to understand the polymer chain extension through RAFT polymerization under dispersion conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Functionalization of iron oxide magnetic nanoparticles with poly(methyl methacrylate) brushes via grafting‐from atom transfer radical polymerization

A key problem with nanomaterials is the difficulty of controlling the dispersion of nanoparticles inside an organic medium. To overcome this problem, functionalization of the nanoparticle surface is required. Poly(methyl methacrylate) (PMMA) brushes were grown on the surface of iron oxide magnetic nanoparticles with atom transfer radical polymerization and a grafting‐from approach. Modified magnetic nanoparticles with a graft density of 0.1 PMMA chains/nm² were obtained. Cu(II), used as a deactivating complex, allowed good control of the polymerization along with a narrow polydispersity of the polymer chains. The functionalized magnetic nanoparticles were characterized with Fourier transform infrared spectroscopy, thermogravimetric analysis, gel permeation chromatography, and atomic force microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 925–932, 2007     

Synthesis of poly(methyl methacrylate)‐b‐polystyrene containing a crown ether unit at the junction point via combination of atom transfer radical polymerization and nitroxide mediated radical polymerization routes

Poly(methyl methacrylate)‐b‐polystyrene (PMMA‐b‐PS) containing a benzo‐15‐crown‐5 unit at the junction point was prepared by combining atom transfer radical polymerization and nitroxide‐mediated radical polymerization. For this purpose, 6,7,9,10,12,13,15,16‐octahydro‐5,8,11,14,17‐pentaoxa‐benzocyclopentadecene‐2‐carboxylic acid 3‐(2‐bromo‐2‐methyl‐propionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethyl‐piperidin‐1‐yloxy)‐ethoxycarbonyl]‐propyl ester ( 3 ) was synthesized and used as an initiator in atom transfer radical polymerization of methyl methacrylate in the presence of CuCl and pentamethyldiethylenetriamine at 60°C. A linear behavior was observed in both plots of ln([M]₀/[M]) versus time and M_n,_GPC versus conversion indicating that the polymerization proceeded in a controlled/living manner. Thus obtained PMMA precursor was used as a macroinitiator in nitroxide‐mediated radical polymerization of styrene (St) at 125°C to give well‐defined PMMA‐b‐PS with crown ether per chain. Kinetic data were also obtained for copolymerization. Moreover, potassium picrate (K⁺ picrate) complexation of 3 and PMMA‐b‐PS copolymer was studied. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3242–3249, 2006     

A new photoiniferter/RAFT agent for ambient temperature rapid and well‐controlled radical polymerization

Phenacyl morpholine‐4‐dithiocarbamate is synthesized and characterized. Its capability to act as both a photoiniferter and reversible addition fragmentation chain transfer agent for the polymerization of styrene is examined. Polymerization carried out in bulk under ultra violet irradiation at above 300 nm at room temperature shows controlled free radical polymerization characteristics up to 50% conversions and produces well‐defined polymers with molecular weights close to those predicted from theory and relatively narrow poyldispersities (M_w/M_n ～ 1.30). End group determination and block copolymerization with methyl acrylate suggest that morpholino dithiocarbamate groups were attained at the end of the polymer. Photolysis and polymerization studies revealed that polymerization proceeds via both reversible termination and RAFT mechanisms. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3387–3395, 2008     

Synthesis of polymeric core–shell particles using surface‐initiated living free‐radical polymerization

An easy and novel approach to the synthesis of functionalized nanostructured polymeric particles is reported. The surfactant‐free emulsion polymerization of methyl methacrylate in the presence of the crosslinking reagent 2‐ethyl‐2‐(hydroxy methyl)‐1,3‐propanediol trimethacrylate was used to in situ crosslink colloid micelles to produce stable, crosslinked polymeric particles (diameter size ～ 100–300 nm). A functionalized methacrylate monomer, 2‐methacryloxyethyl‐2′‐bromoisobutyrate, containing a dormant atom transfer radical polymerization (ATRP) living free‐radical initiator, which is termed an inimer (initiator/monomer), was added to the solution during the polymerization to functionalize the surface of the particles with ATRP initiator groups. The surface‐initiated ATRP of different monomers was then carried out to produce core–shell‐type polymeric nanostructures. This versatile technique can be easily employed for the design of a wide variety of polymeric shells surrounding a crosslinked core while keeping good control over the sizes of the nanostructures. The particles were characterized with scanning electron microscopy, transmission electron microscopy, optical microscopy, dynamic light scattering, and Raman spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1575–1584, 2007     

Synthesis of high molecular weight and narrow molecular weight distribution poly(acrylonitrile) via RAFT polymerization

Well‐defined polyacrylonitrile (PAN) of high viscosity‐average molecular weight (M_η = 405,100 g/mol) was successfully synthesized using reversible addition‐fragmentation chain transfer polymerization. The polymerization exhibits controlled characters: molecular weights of the resultant PANs increasing approximately linearly with monomer conversion and keeping narrow molecular weight distributions. The addition of 0.01 equiv (relative to monomer acrylonitrile) of Lewis acid AlCl₃ in the polymerization system afforded the obtained PAN with an improved isotacticity (by 8%). In addition, the influence of molecular weights and molecular weight distributions of PANs on the morphology of the electrospun fibers was investigated. The results showed that, under the same conditions of electrospinning, average diameter (247–1094 nm) of fibers increased with molecular weights of PANs, and it was much easier to get “uniform” diameter fibers while using PANs with narrow molecular weight distributions as the precursor of electrospinning. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Facile synthesis of poly(hydroxyethyl acrylate) by frontal free‐radical polymerization

We report the first synthesis of poly(hydroxyethyl acrylate) (PHEA) without solvent by free‐radical frontal polymerization (FP) at ambient pressure. In a typical run, the appropriate amounts of reactant (hydroxyethyl acrylate) and initiator (1,1‐di(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane) (Luperox 231) were mixed together at ambient pressure. FP was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self‐propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. To study the macrokinetics, we also produced PHEA frontally with ammonium persulfate as initiator and dimethyl sulfoxide as the solvent. The dependences of the front velocity and front temperature on the initiator concentration and reactant dilution were investigated. The front temperatures were between 124 and 157 °C, depending on the ammonium persulfate concentration. Thermogravimetric analysis indicates that PHEA prepared by FP with ammonium persulfate as initiator had higher thermal stability than solvent‐free frontally prepared PHEA with Luperox 231 as initiator. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 873–881, 2007     

Synthesis of linear and starlike polymers from poly(propylene glycol) methacrylate using controlled radical polymerization

The copper‐catalyzed atom transfer radical polymerization (ATRP) of poly(propylene glycol) methacrylate (PPGM) in solution to produce linear and starlike polymers is reported, using methylethyl ketone as the solvent and a temperature of 80 °C. The ATRP system used was efficient for polymerization of the functionalized monomer without protecting hydroxyl end groups of monomer. The polymerizations were consistent with “living” or controlled processes, as revealed by the linear evolution of molecular weight with conversion. Increasing the [M]₀:[I]₀ ratio resulted in increasing molecular weights, whereas the polydispersity indices remained low (M_w/M_n < 1.4) even at high conversion. Decreasing the [CuBr]₀:[I]₀ ratio resulted in lower conversions, slightly larger polydispersities, and decreased molecular weights, likely resulting from a lower initiation efficiency. Polymers were characterized by ¹H and ¹³C NMR; molecular weights of polymers with low degrees of polymerization were estimated by end‐group analysis from ¹³C NMR spectra obtained using distortionless enhancement by polarization transfer and the gated decoupling techniques. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 334–343, 2002     

Synthesis of well‐designed polymers carrying saccharide moieties via RAFT miniemulsion polymerization

Two hydrophobic vinyl saccharide monomers based on D ‐glucose and D ‐fructose were polymerized by employing the reversible addition‐fragmentation transfer (RAFT) miniemulsion polymerization technique to prepare well‐designed glycopolymers. Three dithiobenzoate‐RAFT agents [S?C(Ph)S? R], 1‐phenylethyl dithiobenzoate (PED), 2‐phenylprop‐2‐yl dithiobenzoate (PPD), and 2‐cyanoprop‐2‐yl dithiobenzoate (CPD), were used to control the growth of polymer chains. The best results were obtained in the presence of the PPD‐RAFT agent and the formed polymers have polydispersity index's (PDI) lower than 1.15. Under adequate miniemulsion polymerization conditions, a glycopolymer with PDI of 1.1 and molecular weight of 5 × 10⁴ g/mol has been successfully synthesized in a short reaction time of 100 min. Furthermore, some block copolymers containing saccharide segment with butyl or methyl methacrylate were prepared. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of bio‐based poly(N‐phenylitaconimide) by atom transfer radical polymerization

Poly(N‐phenylitaconimide) (polyPhII) was prepared using initiators for continuous activator regeneration atom transfer radical polymerization of PhII using FeBr₃ complexes as catalysts. Conversion reached 69% in 24 h, yielding polyPhII with a number average molecular weight M_n = 11,900 and a molecular weight distribution M_w/M_n = 1.52. Copolymerizations of PhII with styrene at various molar ratios were performed providing a range of polyPhII‐copolySt polymers. When the copolymerization was carried out with higher [St]₀ > [PhII]₀ ratio, a one‐pot synthesis of poly(St‐alt‐PhII)‐b‐polySt was achieved. The thermal properties of the obtained copolymers were studied by differential scanning calorimetry. PolyPhII prepared by ATRP showed high glass transition temperature (T_g) of 216 °C and the poly(St‐alt‐PhII)‐b‐polySt exhibited two T_gs, at 162 and 104 °C, corresponding to a poly(St‐alt‐PhII) and polySt segments, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 822–827