Functionalization of multiwalled carbon nanotube via surface reversible addition fragmentation chain transfer polymerization and as lubricant additives

Polymer‐grafted multiwalled carbon nanotube (MWCNT) hybrid composite which possess a hard backbone of MWCNT and a soft shell of brush‐like polystyrene (PSt) were synthesized. The reversible addition fragmentation chain transfer (RAFT) agents were successfully immobilized onto the surface of MWCNT first, and PSt chains were subsequently grafted from sidewall of MWCNT via RAFT polymerization. Chemical structure of resulting product and the quantities of grafted polymer were determined by Fourier transform infrared, thermal gravimetric analysis, nuclear magnetic resonance, and X‐ray photoelectron spectra. Transmission electron microscopy and field emission scanning electron microscopy images clearly indicate that the nanotubes were coated with a polymer layer. Furthermore, the functionalized MWCNT as additives was added to base lubricant and the tribological property of resultant MWCNT lubricant was investigated with four‐ball machines. The results indicate that the functionalization led to an improvement in the dispersion of MWCNT and as additives it amended the tribological property of base lubricant. The mechanism of the significant improvements on the tribological properties of the functionalized MWCNT as additives was discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3014–3023, 2008     

Isoprene polymerization via reversible addition fragmentation chain transfer polymerization

Until recently, the primary living radical polymerization method available for preparing polyisoprene was nitroxide‐mediated radical polymerization, with reversible addition‐fragmentation chain transfer polymerization being applied only in a few cases within the last couple of years. We report here the preparation of polyisoprene by RAFT in the presence of the trithiocarbonate transfer agent S‐1‐dodecyl‐S′‐(r,r′‐dimethyl‐r′′‐acetic acid)trithiocarbonate and t‐butyl peroxide as the radical initiator. The kinetics of this polymerization at an optimized temperature of 125 °C and radical initiator concentration of 0.2 equiv relative to transfer agent have been studied in triplicate and demonstrate the living nature of the polymerization. These conditions resulted in polymers with narrow polydispersity indices, on the order of 1.2, with monomer conversions up to 30%. Retention of chain‐end functionality was demonstrated by polymerizing styrene as a second block from a polyisoprene macrotransfer agent, resulting in a block copolymer presenting a unimodal gel permeation chromatogram, and narrow molecular weight distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4100–4108, 2007     

The future of reversible addition fragmentation chain transfer polymerization

We examine the reversible addition fragmentation chain transfer (RAFT) process with regard to its potential and limits in future industrial applications (including those conducted on a larger scale) as well as materials science. The outlook for the RAFT process is bright: Its unrivaled inherent process simplicity coupled with a wide tolerance to monomer classes and functionalities makes it a prime candidate for the use in large reactors. At the same time, it allows for ready access to complex macromolecular architectures of variable shape and size. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5715–5723, 2008     

Synthesis of poly(methyl acrylate) loops grafted onto silica nanoparticles via reversible addition‐fragmentation chain transfer polymerization

Reversible addition‐fragmentation chain transfer (RAFT) polymerization was used to produce poly(methyl acrylate) (pMA) loops grafted onto silica nanoparticles using doubly anchored bifunctional RAFT agents 1,4‐bis(3′‐trimethoxysilylpropyltrithiocarbonylmethyl)benzene (Z‐group approach) and 1,6‐bis(o,p‐2′‐trimethoxysilylethylbenzyltrithiocarbonyl)hexane (R‐group approach) as mediators. In both cases, molecular weights of the resulting surface‐confined polymer loops increased with monomer conversion, whereas the grafting density was significantly higher in the case of the R‐group supported RAFT polymerization due to mechanistic differences of the RAFT process at the surface. This result was evident from thermogravimetric analysis and supported by scanning electron microscopy. Polymer loops with molecular weights up to 53,000 g mol^?1 were accessible with polydispersities of about 2.0 without and 1.5 with the addition of free RAFT agent. UV signals of the detached pMA loops measured via size exclusion chromatography were shifted to higher molecular weights compared with the corresponding RI signals, indicating branching reactions caused by the close proximity of growing radicals and polymer at the surface of the silica nanoparticles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7656–7666, 2008     

Synthesis of polymer with defined fluorescent end groups via reversible addition fragmentation transfer polymerization for characterizing the conformations of polymer chains in solutions

A new type of chain transfer agent used in reversible addition fragmentation chain transfer (RAFT) polymerization named 9‐anthracenylmethyl (4‐cyano‐4‐(N‐carbazylcarbodithioate) pentanoate) (ACCP) was synthesized with a total yield over 75% by the incorporation of both fluorescent donor and acceptor chromophores. Polymerization of heterotelechelic α,ω end‐labeled dye‐functionalized polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(n‐butyl methacrylate) (PBMA) with adjustable molecular weights and narrow polydispersity could be conducted by a one‐pot procedure through RAFT polymerization with this bischromophore chain transfer agent. The polymerizations demonstrated “living” controlled characteristics. By taking advantage of the characteristic fluorescence resonance energy transfer (FRET) response between the polymer chain terminals, the variation of chain dimensions in solution from the dilute region to the semidilute region can be monitored by changes in the ratio of the fluorescence intensities of the carbazolyl group to the anthryl group, which lends itself to potential applications in characterizing chain dimensions in solutions for thermodynamic or dynamic studies. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2413–2420     

Dendrimer‐star polymer and block copolymer prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization with dendritic chain transfer agent

A new reversible addition‐fragmentation chain transfer (RAFT) agent, dendritic polyester with 16 dithiobenzoate terminal groups, was prepared and used in the RAFT polymerization of styrene (St) to produce star polystyrene (PSt) with a dendrimer core. It was found that this polymerization was of living characters, the molecular weight of the dendrimer‐star polymers could be controlled and the polydispersities were narrow. The dendrimer‐star block copolymers of St and methyl acrylate (MA) were also prepared by the successive RAFT polymerization using the dendrimer‐star PSt as macro chain transfer agent. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6379–6393, 2005     

Synthesis of ω‐sulfonated polystyrene via reversible addition fragmentation chain transfer polymerization and postpolymerization modification

The synthesis of chain‐end sulfonated polystyrene [PS (ω‐sulfonated PS)] by reversible addition fragmentation chain transfer (RAFT) polymerization followed by postpolymerization modification was investigated by two methods. In the first method, the polymer was converted to a thiol‐terminated polymer by aminolysis. This polymer was then sulfonated by oxidation of the thiol end‐group with m‐chloroperoxybenzoic acid (m‐CPBA) to produce a sulfonic acid end‐group. In the second method, the RAFT‐polymerized polymer was directly sulfonated by oxidation with m‐CPBA. After purification by column chromatography, ω‐sulfonated PS was obtained by both methods with greater than 95% end‐group functionality as measured by titration. The sulfonic acid end‐group could be neutralized with various ammonium or imidazolium counter ions through acid–base or ionic metathesis reactions. The effect of the ionic end‐groups on the glass transition temperature of the PS was found to be consistent with what is known for PS ionomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Kinetic model of reversible addition fragmentation chain transfer polymerization of styrene in seeded emulsion

A detailed model describing the kinetics of living polymerization mediated by reversible addition‐fragmentation chain transfer (RAFT) in seeded emulsion polymerization is developed. The model consists of a set of population balance equations of the different radical species in the aqueous phase and in the particle phase (accounting for radical segregation) as well as for the dormant species in the particle phase. The entire population of radicals was divided into several distinguished species, based on their length and their chain end group. The model results are helpful in understanding inhibition and retardation phenomena that are typical for RAFT emulsion polymerizations. While inhibition is due to the radical loss in form of the RAFT leaving group, retardation is mostly caused by a small amount of short dormant chains in the particle phase, leading to a slight increase of radical loss via RAFT exchange with radicals entering a particle. The model results are compared to a series of experiments, using cumyl dithiobenzoate as a RAFT agent in polymerizations of styrene. The agreement between experimental and model results is good and, notably, the only parameters considered adjustable were the RAFT exchange rate coefficients. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6114–6135, 2006     

Synthetic and characterization aspects of dimethylaminoethyl methacrylate reversible addition fragmentation chain transfer (RAFT) polymerization

2‐cyanoprop‐2‐yl dithiobenzoate (CPDB) mediated RAFT polymerization of dimethylaminoethyl methacrylate (DMAEMA) was carried out in dioxane at 90 °C. The influence of several parameters, such as the monomer to CPDB molar ratio (100 to 500), the monomer concentration (2 mol·L^?1 to 5.9 mol·L^?1), and CPDB to initiator molar ratio (1 to 10), was evaluated with regards to conversion and polymerization duration, as well as control of molar mass and molar mass distributions. Number average molar masses from 10,000 to 70,000 g·mol^?1 can be targeted. The determination of the molar masses has been carried out by size exclusion chromatography (SEC) with a refractometer detector with poly(methyl methacrylate) (PMMA) standards. The experimental values were lower than the expected ones. Then, SEC in aqueous medium with an online laser light scattering detector was used both to get absolute molar masses and to recalibrate the SEC column in THF. Characterization of well‐controlled PDMAEMA samples has been performed by proton NMR spectroscopy and matrix assisted laser desorption ionization time of flight mass spectrometry. Finally, a chain extension experiment was evaluated with regard to living features. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3551–3565, 2005     

可逆加成-断裂链转移策略制备可识别转铁蛋白的抗原决定基印迹微球

应用可逆加成-断裂链转移（RAFT）策略制备了一种抗原决定基表面印迹微球。这一工作以转铁蛋白的抗原决定基N端九肽作为模板,通过共价键合的方式固载于修饰了戊二醛的硅胶颗粒表面。然后以甲基丙烯酸、甲基丙烯酰羟乙酯为功能单体,甲叉基双丙烯酰胺为交联剂,偶氮二异丁腈（AIBN）为引发剂,N,N-二甲基甲酰胺为溶剂,在三硫酯试剂2-（十二烷基三硫代碳酸酯基）-2-甲基丙酸的调控下,于70 ℃进行活性-可控的聚合反应,制备得到分子印迹微球。该材料对模板抗原决定基的识别容量为2.36 mg/g,印迹因子为1.89;对转铁蛋白的识别容量为4.98 mg/g,印迹因子为1.61,120 min内可达到吸附平衡;在多蛋白质竞争识别中,该材料对转铁蛋白识别的印迹因子远高于细胞色素C、乳球蛋白等其他竞争蛋白质的印迹因子。以上结果证明,通过RAFT策略制备得到的抗原决定基分子印迹材料在对抗原决定基具有良好的识别能力的同时,对模板抗原决定基对应的转铁蛋白也具有优良的选择性、较高的识别容量和较快的识别速度。     

Simultaneous reversible addition fragmentation chain transfer and ring‐opening polymerization

The simultaneous ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) and 2‐hydroxyethyl methacrylate (HEMA) polymerization via reversible addition fragmentation chain transfer (RAFT) chemistry and the possible access to graft copolymers with degradable and nondegradable segments is investigated. HEMA and ε‐CL are reacted in the presence of cyanoisopropyl dithiobenzoate (CPDB) and tin(II) 2‐ethylhexanoate (Sn(Oct)₂) under typical ROP conditions (T > 100 °C) using toluene as the solvent in order to lead to the graft copolymer PHEMA‐g‐PCL. Graft copolymer formation is evidenced by a combination of size‐exclusion chromatography (SEC) and NMR analyses as well as confirmed by the hydrolysis of the PCL segments of the copolymer. With targeted copolymers containing at least 10% weight of PHEMA and relatively small PHEMA backbones (ca. 5,000–10,000 g mol^?1) the copolymer grafting density is higher than 90%. The ratio of free HEMA‐PCL homopolymer produced during the “one‐step” process was found to depend on the HEMA concentration, as well as the half‐life time of the radical initiator used. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3058–3067, 2008     

Macromolecular design via reversible addition–fragmentation chain transfer (RAFT)/xanthates (MADIX) polymerization

Among the living radical polymerization techniques, reversible addition–fragmentation chain transfer (RAFT) and macromolecular design via the interchange of xanthates (MADIX) polymerizations appear to be the most versatile processes in terms of the reaction conditions, the variety of monomers for which polymerization can be controlled, tolerance to functionalities, and the range of polymeric architectures that can be produced. This review highlights the progress made in RAFT/MADIX polymerization since the first report in 1998. It addresses, in turn, the mechanism and kinetics of the process, examines the various components of the system, including the synthesis paths of the thiocarbonyl‐thio compounds used as chain‐transfer agents, and the conditions of polymerization, and gives an account of the wide range of monomers that have been successfully polymerized to date, as well as the various polymeric architectures that have been produced. In the last section, this review describes the future challenges that the process will face and shows its opening to a wider scientific community as a synthetic tool for the production of functional macromolecules and materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:5347–5393, 2005     

Preparation,characterization, and chiral recognition of optically active polymers containing pendent chiral units via reversible addition‐fragmentation chain transfer polymerization

Optically active polymers bearing chiral units at the side chain were prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization in the presence of 2,2′‐azobisisobutyronitrile (AIBN)/benzyl dithiobenzoate (BDB), using a synthesized 6‐O‐p‐vinylbenzyl‐1,2:3,4‐Di‐O‐isopropylidene‐D ‐galactopyranose (VBPG) as the monomer. The experimental results suggested that the polymerization of the monomer proceeded in a living fashion, providing chiral group polymers with narrow molecular weight distributions. The optically active nature of the obtained poly (6‐O‐p‐vinylbenzyl‐1,2:3,4‐Di‐O‐isopropylidene‐D ‐galactopyranose) (PVBPG) was studied by investigating the dependence of specific rotation on the molecular weight of PVBPG and the concentration of PVBPG in tetrahydrofuran (THF). The results showed the specific rotation of PVBPG increased greatly with the decrease of the concentration of the PVBPG homopolymer. In addition, the effect of block copolymers of PVBPG on the optically active nature was also investigated by preparing a series of diblock copolymers of poly(methyl methacrylate) (PMMA)‐b‐PVBPG, polystyrene (PS)‐b‐PVBPG, and poly(methyl acrylate) (PMA)‐b‐PVBPG. It was found that both the homopolymer and the diblock copolymers possessed specific rotations. Finally, the ability of chiral recognition of the PVBPG homopolymer was investigated via an enantiomer‐selective adsorption experiment. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3788–3797, 2007     

A cyclic selenium‐based reversible addition‐fragmentation chain transfer agent mediated polymerization of vinyl acetate

A cyclic selenium‐based reversible addition‐fragmentation chain transfer (RAFT) agent, 5,5‐dimethyl‐3‐phenyl‐2‐selenoxo‐1,3‐selenazolidin‐4‐one (RAFT‐Se), was synthesized and utilized in the RAFT polymerizations of vinyl acetate (VAc). Its analog, 5,5‐dimethyl‐3‐phenyl‐2‐thioxothiazolidin‐4‐one (RAFT‐S), was also used in RAFT polymerizations for comparison under identical conditions. The RAFT polymerizations of VAc with RAFT‐Se were moderately controlled evidenced by the increase of molecular weights with conversion, despite the slightly high M_w/M_n (less than 1.90), whereas the molecular weights were poorly controlled in the presence of RAFT‐S (2.00 < M_w/M_n < 2.30). Thanks to its unusual cyclic structure of RAFT‐Se, one or more RAFT‐Se species was incorporated into the resultant poly(VAc) as revealed by the results of cleavage of polymer and atomic absorption spectroscopy. Considering the biorelated functions of both poly(VAc) and Se element, this work undoubtedly provided a successful methodology of how to incorporate high content of Se into a molecular weight controlled poly(VAc). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of cationic N‐[3‐(dimethylamino)propyl]methacrylamide brushes on silicon wafer via surface‐initiated RAFT polymerization

Surface‐initiated reversible addition‐fragmentation chain transfer (SI‐RAFT) polymerization of N‐[3‐(dimethylamino)propyl]methacrylamide (DMAPMA) on the silicon wafer was conducted in attempt to create controllable cationic polymer films. The RAFT agent‐immobilized substrate was prepared by the silanization of hydroxyl groups on silicon wafer with 3‐aminopropylthriethoxysilane (APTS) and by the amide reaction of amine groups of APTS with ester groups of 4‐cyano‐4‐((thiobenzoyl) sulfanyl) pentanoic succinimide ester (CPSE); followed by the RAFT polymerization of DMAPMA using a “free” RAFT agent, that is, 4‐cyanopentanoic acid dithiobenzoate (CPAD) and an initiator, that is, 4,4′‐azobis‐4‐cyanopentanoic acid (CPA). The formation of homogeneous tethered poly(N‐[3‐(dimethylamino)propyl]methacrylamide) [poly(DMAPMA)] brushes, whose thickness can be tuned by reaction time varying, is evidenced by using the combination of grazing angle attenuated total reflectance‐Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, and water contact‐angle measurements. The calculation of grafting parameters from the number‐average molecular weight, M _n (g/mol) and ellipsometric thickness, h (nm) values indicated the synthesis of densely grafted poly(DMAPMA) films and allowed us to predict a polymerization time for forming a “brush‐like” conformation for the chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of thermo‐responsive 4‐arm star‐shaped porphyrin‐centered poly(N,N‐diethylacrylamide) via reversible addition‐fragmentation chain transfer radical polymerization

Tetrafunctional porphyrins‐containing trithiocarbonate groups were synthesized by an ordinary esterification method. This tetrafunctional porphyrin (TPP‐CTA) could be used as a chain transfer agent in a controlled reversible addition‐fragmentation chain transfer (RAFT) radical polymerization to prepare well‐defined 4‐arm star‐shaped polymers. N,N‐Diethylacrylamide was polymerized using TPP‐CTA in 1,4‐dioxane. Poly(N,N‐diethylacrylamide) (PDEA) is known to be a thermo‐responsive polymer, and exhibits a lower critical solution temperature (LCST) in water. The star‐shaped PDEA polymer (TPP‐PDEA) was therefore also thermo‐responsive, as expected. The LCST of this polymer depended on its concentration in water, as confirmed by turbidity, dynamic light scattering (DLS), static light scattering (SLS), and ¹H NMR measurements. The porphyrin cores were compartmentalized in PDEA shells in aqueous media. Below the LCST, the fluorescence intensity of TPP‐PDEA was about six times larger than that of a water‐soluble low molecular weight porphyrin compound (TSPP), whose fluorescence intensity was independent of temperature. Above the LCST, the fluorescence intensity of TPP‐PDEA decreased, while the intensity was about three times higher than that of TSPP. These observations suggested that interpolymer aggregation occurred due to the hydrophobic interactions of the dehydrated PDEA arm chains above the LCST, with self‐quenching of the porphyrin moieties arising from these interactions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Synthesis and characterization of fluorescence end‐labeled polystyrene via reversible addition‐fragmentation chain transfer (RAFT) polymerization

Fluorescence end‐labeled polystyrene (PS) with heteroaromatic carbazole or indole group were prepared conveniently via reversible addition‐fragmentation chain transfer (RAFT) polymerization using dithiocarbamates, ethyl 2‐(9H‐carbazole‐9‐carbonothioylthio)propanoate (ECCP) and benzyl 2‐phenyl‐1H‐indole‐1‐carbodithioate (BPIC) as RAFT agents. The end functionality of obtained PS with different molecular weights was high. The steady‐state and the time‐resolved fluorescence techniques had been used to study the fluorescence behaviors of obtained end‐labeled PS. The fluorescence of dithiocarbamates resulting PS in solid powder cannot be monitored; however, they exhibited structured absorptions and emissions in solvent DMF and the fluorescence lifetimes of PS had no obvious change with molecular weights increasing. These observations suggested that the polymer chains were possibly stretched adequately in DMF, that is, the fluorescence end group was exposed into solvent molecules and little quenching of excited state occurred upon incorporation into polymer chain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6198–6205, 2008