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Chain Transfer (chain + transfer)
Kinds of Chain Transfer Terms modified by Chain Transfer Selected AbstractsAb initio Emulsion Polymerization by RAFT (Reversible Addition,Fragmentation Chain Transfer) through the Addition of CyclodextrinsHELVETICA CHIMICA ACTA, Issue 8 2006Bojana Apostolovic Abstract A novel process to produce homo- and copolymers by RAFT polymerization in emulsion is presented. It is known that RAFT-controlled radical polymerization can be conducted in emulsion polymerization without disturbing the radical segregation characteristic of this process, thus leading to polymerization rates identical to those encountered in the corresponding nonliving systems. However, RAFT agents are often characterized by very low water solubility and, therefore, they diffuse very slowly from the monomer droplets, where they are initially solubilized, to the reaction loci, i.e., the polymer particles. Accordingly, when used in emulsion polymerization, they are practically excluded from the reaction. In this work, we show that cyclodextrins, well-known for their ability to form water-soluble complexes with hydrophobic molecules, facilitate the transport across the H2O phase of the RAFT agent to the polymer particles. Accordingly, chains grow through the entire process in a controlled way. This leads to the production of low-polydispersity polymers with well-defined structure and end functionalities as well as to the possibility of synthesizing block copolymers by a radical mechanism. [source] Synthesis of comb polymers via grafting-onto macromolecules bearing pendant diene groups via the hetero-Diels-Alder-RAFT click conceptJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2010Antoine Bousquet Abstract Comb polymers were synthesized by the "grafting-onto" method via a combination of Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization and the hetero-Diels-Alder (HDA) cycloaddition. The HDA reactive monomer trans, trans-hexa-2,4-dienylacrylate (ttHA) was copolymerized with styrene via the RAFT process. Crosslinking was minimized by decreasing the monomer concentration,whilst keeping monomer to polymer conversions low,resulting in reactive backbones with on average one reactive pendant diene groups for 10 styrene units. The HDA cycloaddition was performed between the diene functions of the copolymer and a poly(n -butyl acrylate) (PnBA) prepared via RAFT polymerization with pyridin-2-yldithioformate, which can act as a dienophile. The coupling reactions were performed within 24 h at 50 °C and the grafting yield varies from 75% to 100%, depending on the number average molecular weight of the PnBA (3500 g mol,1 < Mn < 13,000 g mol,1) grafted chain and the reaction stoichiometry. The molecular weights of the grafted block copolymers range from 19,000 g mol,1 to 58,000 g mol,1 with polydispersities close to 1.25. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1773,1781, 2010 [source] Synthesis of Poly(lauryl acrylate) by Single-Electron Transfer/Degenerative Chain Transfer Living Radical Polymerization Catalyzed by Na2S2O4 in WaterMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2007Jorge F. J. Coelho Abstract Living radical polymerization of lauryl acrylate was achieved by SET/DTLRP in water catalyzed by sodium dithionite. The work describes the synthesis of a highly hydrophobic and polar monomer in aqueous medium. The plots of versus conversion and ln[M]0/[M] versus time are linear, indicating a controlled polymerization. This method leads to ,,, -diiodopoly(lauryl acrylate)s that can be further functionalized. The MWDs were determined using a combination of three detectors: RALLS, DV, and RI. The method studied in this work represents a possible route to prepare well-tailored macromolecules made of LA in environment friendly reaction medium. The syndiotactic content is 75%. [source] Chain Transfer to Polymer and Branching in Controlled Radical Polymerizations of n -Butyl AcrylateMACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2009Nasir M. Ahmad Abstract Chain transfer to polymer (CTP) in conventional free-radical polymerizations (FRPs) and controlled radical polymerizations (ATRP, RAFT and NMP) of n -butyl acrylate (BA) has been investigated using 13C NMR measurements of branching in the poly(n -butyl acrylate) produced. The mol-% branches are reduced significantly in the controlled radical polymerizations as compared to conventional FRPs. Several possible explanations for this observation are discussed critically and all except one refuted. The observations are explained in terms of differences in the concentration of highly reactive short-chain radicals which can be expected to undergo both intra- and inter-molecular CTP at much higher rates than long-chain radicals. In conventional FRP, the distribution of radical concentrations is broad and there always is present a significant proportion of short-chain radicals, whereas in controlled radical polymerizations, the distribution is narrow with only a small proportion of short-chain radicals which diminishes as the living chains grow. Hence, irrespective of the type of control, controlled radical polymerizations give rise to lower levels of branching, when performed under otherwise similar conditions to conventional FRP. Similar observations are expected for other acrylates and monomers that undergo chain transfer to polymer during radical polymerization. [source] A Strategy for Synthesis of Ion-Bonded Supramolecular Star Polymers by Reversible Addition-Fragmentation Chain Transfer (RAFT) PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2008Kang Tao Abstract We have developed a novel strategy for the preparation of ion-bonded supramolecular star polymers by RAFT polymerization. An ion-bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert -butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by 1H NMR and GPC. The results show that the polymerization possesses the character of living free-radical polymerization and the ion-bonded supramolecular star polymers PSt, PtBA, and PSt- b -PtBA, with six well-defined arms, were successfully synthesized. [source] Experimental Requirements for an Efficient Control of Free-Radical Polymerizations via the Reversible Addition-Fragmentation Chain Transfer (RAFT) Process,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2006Arnaud Favier Abstract Summary: Reversible addition-fragmentation chain transfer (RAFT) polymerization is a recent and very versatile controlled radical polymerization technique that has enabled the synthesis of a wide range of macromolecules with well-defined structures, compositions, and functionalities. The RAFT process is based on a reversible addition-fragmentation reaction mediated by thiocarbonylthio compounds used as chain transfer agents (CTAs). A great variety of CTAs have been designed and synthesized so far with different kinds of substituents. In this review, all of the CTAs encountered in the literature from 1998 to date are reported and classified according to several criteria : i) the structure of their substituents, ii) the various monomers that they have been polymerized with, and iii) the type of polymerization that has been performed (solution, dispersed media, surface initiated, and copolymerization). Moreover, the influence of various parameters is discussed, especially the CTA structure relative to the monomer and the experimental conditions (temperature, pressure, initiation, CTA/initiator ratio, concentration), in order to optimise the kinetics and the efficiency of the molecular-weight-distribution control. Schematic of the RAFT polymerization. [source] Chain Transfer and Efficiency of End-Group Introduction in Free Radical Polymerization of Methyl Methacrylate in the Presence of Poly(methyl methacrylate) MacromonomerMACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2004Kazuki Miyake Abstract Summary: Experimental and modeling studies of addition,fragmentation chain transfer (AFCT) during radical polymerization of methyl methacrylate in the presence of poly(methyl methacrylate) macromonomer with 2-carbomethoxy-2-propenyl , -ends (PMMA-CO2Me) at 60,°C are reported. The results revealed that AFCT involving PMMA-CO2Me formed in situ during methyl methacrylate polymerization has a negligible effect on the molecular weight distribution. [source] Addition-Fragmentation Chain Transfer to Polymer in the Free Radical Ring-Opening Polymerization of an Eight-membered Cyclic Allylic Sulfide MonomerMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2005Marisa Phelan Abstract Summary: A detailed investigation of chain transfer to polymer during free radical ring-opening polymerization of the eight-membered disulfide monomer 2-methyl-7-methylene-1,5-dithiacyclooctane (MDTO) is presented. It has been shown that extensive chain transfer to polymer occurs involving both poly(MDTO) radicals and cyanoisopropyl radicals. Significant decreases in molecular weight were observed when cyanoisopropyl radicals were generated in the presence of poly(MDTO) in the absence of monomer. The molecular weight distribution (MWD) obtained from polymerization of MDTO in the presence of pre-added poly(MDTO) was markedly different from that obtained without pre-added polymer. A kinetic model was constructed in an attempt to quantitatively describe the chain transfer to polymer process based on the addition fragmentation chain transfer mechanism. It was found however that the simulated MWDs were considerably broader than the experimental MWDs, which were similar to the Schulz-Flory distribution. Mechanism for chain transfer to polymer. [source] Chain transfer to ionic liquid in an anionic polymerization of methyl methacrylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2007Tadeusz Biedro When methyl methacrylate is polymerized with alkyllithium as initiator in imidazolium ionic liquids, low molecular weight polymers are formed in high yield. The head-groups are, however, not those alkyl groups that are present in alkyllithium, but predominantly those that are originally present at 1-position in imidazolium cation indicating extensive chain transfer to imidazolium ionic liquid. [source] Chain Transfer to Polymer and Branching in Controlled Radical Polymerizations of n -Butyl AcrylateMACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2009Nasir M. Ahmad Abstract Chain transfer to polymer (CTP) in conventional free-radical polymerizations (FRPs) and controlled radical polymerizations (ATRP, RAFT and NMP) of n -butyl acrylate (BA) has been investigated using 13C NMR measurements of branching in the poly(n -butyl acrylate) produced. The mol-% branches are reduced significantly in the controlled radical polymerizations as compared to conventional FRPs. Several possible explanations for this observation are discussed critically and all except one refuted. The observations are explained in terms of differences in the concentration of highly reactive short-chain radicals which can be expected to undergo both intra- and inter-molecular CTP at much higher rates than long-chain radicals. In conventional FRP, the distribution of radical concentrations is broad and there always is present a significant proportion of short-chain radicals, whereas in controlled radical polymerizations, the distribution is narrow with only a small proportion of short-chain radicals which diminishes as the living chains grow. Hence, irrespective of the type of control, controlled radical polymerizations give rise to lower levels of branching, when performed under otherwise similar conditions to conventional FRP. Similar observations are expected for other acrylates and monomers that undergo chain transfer to polymer during radical polymerization. [source] Quantification of Grafting Densities Achieved via Modular "Grafting-to" Approaches onto Divinylbenzene MicrospheresADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Leena Nebhani Abstract The surface modification of divinylbenzene (DVB)-based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero-Diels,Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this "grafting-to" method. Two variants of the RAFT-HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number-averaged molecular weight, Mn,=,4200,g,mol,1; polydispersity index, PDI,=,1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2,×,1020 chains per gram of microspheres. In the second approach, the functionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (Mn,=,6000,g,mol,1, PDI,=,1.25; Mn,=,26,000,g,mol,1, PDI,=,1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T,=,60,°C) yet in the absence of a catalyst. In this case the surface grafting density is close to 7,chains,nm,2 for Mn,=,6000,g,mol,1 and 4,chains,nm,2 for Mn,=,26,000,g,mol,1, or 2.82,×,1019 and 1.38,×,1019,chains g,1, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry. [source] Temperature Responsive Solution Partition of Organic,Inorganic Hybrid Poly(N -isopropylacrylamide)-Coated Mesoporous Silica Nanospheres,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2008Po-Wen Chung Abstract A series of poly(N -isopropylacrylamide)-coated mesoporous silica nanoparticle materials (PNiPAm-MSNs) has been synthesized by a surface-initiated living radical polymerization with a reversible addition,fragmentation chain transfer (RAFT) reaction. The structure and the degree of polymerization of the PNiPAm-MSNs has been characterized by a variety of techniques, including nitrogen sorption analysis, 29Si and 13C solid-state NMR spectroscopy, transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). The thermally induced changes of the surface properties of these polymer-coated core,shell nanoparticles have been determined by examining their partition activities in a biphasic solution (water/toluene) at different temperatures. [source] Synthesis of Inorganic,Organic Diblock Copolymers as a Precursor of Ordered Mesoporous SiCN Ceramic,ADVANCED MATERIALS, Issue 17 2007D. Nghiem A novel poly(vinyl)silazane- block -polystyrene diblock copolymer is successfully synthesized by living free-radical polymerization via a reversible addition fragmentation chain transfer (RAFT) route (see figure). The obtained diblock copolymer, having an inorganic volume fraction of 0.69, leads to phase-separation at the nanoscale to form an ordered nanostructure, which is converted to well-ordered mesoporous SiCN ceramic after heating at 800,°C and maintained up to 1400,°C. [source] Distribution of acrylic acid grafted chains introduced into polyethylene film by simultaneous radiation grafting with water and ethanol as solventsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Zhengchi Hou Abstract The graft copolymerization of acrylic acid onto low-density polyethylene films by simultaneous ,-ray irradiation was carried out. The effect of water and ethanol as grafting solvents on the distribution of grafted poly (acrylic acid) in the low-density polyethylene films was studied with optical microscopy observations of dyed and sliced samples and attenuated total reflection/Fourier infrared spectroscopy analysis. When no vigorous homopolymerization occurred, both polyethylene and poly(acrylic acid) existed in the grafted layer, and the thickness of the grafted layer and the poly(acrylic acid) concentration in the grafted layer increased with an increasing degree of grafting, regardless of the grafting conditions, the former increasing faster than the latter. In comparison with water as the solvent, in the absence of the inhibitor, homopolymerization could be suppressed to a certain degree in the ethanol solvent system, whereas in the presence of the inhibitor, obvious homopolymerization occurred at a lower monomer concentration, and both the degree of grafting and the thickness of the grafted layer were lower. Such differences could be explained by the chain transfer and the relatively low solubility of poly(acrylic acid) in ethanol. In addition, an experimental scheme using optical microscopy to observe the dyed and sliced polymers was optimized. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1570,1577, 2007 [source] Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2010Wentian Lin Abstract This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl-B-9-borabicyclononane (Me-B-9-BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]-catalyzed ethylene (Cp2ZrCl2 and rac -Me2Si(2-Me-4-Ph)2ZrCl2 as a catalyst) and styrene (Cp*Ti(OMe)3 as catalyst) polymerizations. The two trialkylboranes were found,in most cases,able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)-terminated PE and s -PS polymers after an oxidative workup process, suggesting the formation of the B-polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp2ZrCl2/MAO, whereas it became less effective when the catalyst changed to rac -Me2Si(2-Me-4-Ph)2ZrCl2. Both TEB and Me-B-9-BBN caused an efficient chain transfer in the Cp2ZrCl2/MAO-catalyzed ethylene polymerization; nevertheless, Me-B-9-BBN failed in vain with rac -Me2Si(2-Me-4-Ph)2ZrCl2/MAO. In the case of styrene polymerization with Cp*Ti(OMe)3/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as BH-bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane-terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534,3541, 2010 [source] Synthesis of magnetic, reactive, and thermoresponsive Fe3O4 nanoparticles via surface-initiated RAFT copolymerization of N -isopropylacrylamide and acroleinJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2010Zhong-Peng Xiao Abstract A reversible addition-fragmentation chain transfer (RAFT) agent was directly anchored onto Fe3O4 nanoparticles in a simple procedure using a ligand exchange reaction of S -1-dodecyl- S,-(,,,,-dimethyl-,,-acetic acid)trithiocarbonate with oleic acid initially present on the surface of pristine Fe3O4 nanoparticles. The RAFT agent-functionalized Fe3O4 nanoparticles were then used for the surface-initiated RAFT copolymerization of N -isopropylacrylamide and acrolein to fabricate structurally well-defined hybrid nanoparticles with reactive and thermoresponsive poly(N -isopropylacrylamide- co -acrolein) shell and magnetic Fe3O4 core. Evidence of a well-controlled surface-initiated RAFT copolymerization was gained from a linear increase of number-average molecular weight with overall monomer conversions and relatively narrow molecular weight distributions of the copolymers grown from the nanoparticles. The resulting novel magnetic, reactive, and thermoresponsive core-shell nanoparticles exhibited temperature-trigged magnetic separation behavior and high ability to immobilize model protein BSA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 542,550, 2010 [source] Macromolecular brushes synthesized by "grafting from" approach based on "click chemistry" and RAFT polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2010Dongxia Wu Abstract Well-defined macromolecular brushes with poly(N -isopropyl acrylamide) (PNIPAM) side chains on random copolymer backbones were synthesized by "grafting from" approach based on click chemistry and reversible addition-fragmentation chain transfer (RAFT) polymerization. To prepare macromolecular brushes, two linear random copolymers of 2-(trimethylsilyloxy)ethyl methacrylate (HEMA-TMS) and methyl methacrylate (MMA) (poly(MMA- co -HEMA-TMS)) were synthesized by atom transfer radical polymerization and were subsequently derivated to azide-containing polymers. Novel alkyne-terminated RAFT chain transfer agent (CTA) was grafted to polymer backbones by copper-catalyzed 1,3-dipolar cycloaddition (azide-alkyne click chemistry), and macro-RAFT CTAs were obtained. PNIPAM side chains were prepared by RAFT polymerization. The macromolecular brushes have well-defined structures, controlled molecular weights, and molecular weight distributions (Mw/Mn , 1.23). The RAFT polymerization of NIPAM exhibited pseudo-first-order kinetics and a linear molecular weight dependence on monomer conversion, and no detectable termination was observed in the polymerization. The macromolecular brushes can self-assemble into micelles in aqueous solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 443,453, 2010 [source] Synthesis and kinetic analysis of DPE controlled radical polymerization of MMAJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009Ying-Da Luo Abstract The 1,1-diphenylethene (DPE) controlled radical polymerization of methyl methacrylate was performed at 80 °C by using AIBN as an initiator and DPE as a control agent. It was found that the molecular weight of polymer remained constant with monomer conversion throughout the polymerization regardless of the amounts of DPE and initiator in formulation. To understand the result of constant molecular weight of living polymers in DPE controlled radical polymerization, a living kinetic model was established in this research to evaluate all the rate constants involved in the DPE mechanism. The rate constant k2, corresponding to the reactivation reaction of the DPE capped dormant chains, was found to be very small at 80 °C (1 × 10,5 s,1), that accounted for the result of constant molecular weight of polymers throughout the polymerization, analogous to a traditional free radical polymerization system that polymer chains were terminated by chain transfer. The polydispersity index (PDI) of living polymers was well controlled <1.5. The low PDI of obtained living polymers was due to the fact that the rate of growing chains capped by DPE was comparable with the rate of propagation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source] Synthesis of high glass transition temperature copolymers based on poly(vinyl chloride) via single electron transfer,Degenerative chain transfer mediated living radical polymerization (SET-DTLRP) of vinyl chloride in waterJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009Jorge F. J. Coelho Abstract ,,,-di(iodo) poly(isobornyl acrylate) macroiniators (,,,-di(iodo)PIA) with number average molecular weight from Mn,TriSEC = 11,456 to Mn,TriSEC = 94,361 were synthesized by single electron transfer-degenerative chain transfer mediated living radical polymerization (SET-DTLRP) of isobornyl acrylate (IA) initiated with iodoform (CHI3) and catalyzed by sodium dithionite (Na2S2O4) in water at 35 °C. The plots of number average molecular weight vs conversion and ln{[M]0/[M]} vs time are linear, indicating a controlled polymerization. ,,,-di(iodo) poly(isobornyl acrylate) have been used as a macroinitiator for the SET-DTLRP of vinyl chloride (VCM) leading to high Tg block copolymers PVC-b-PIA-b-PVC. The dynamic mechanical thermal analysis of the block copolymers suggests just one phase indicating that copolymer behaves as a single material. This technology provides the possibility of synthesizing materials based on PVC with higher Tg in aqueous medium. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source] Well-defined amphiphilic graft copolymer consisting of hydrophilic poly(acrylic acid) backbone and hydrophobic poly(vinyl acetate) side chainsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2009Yaogong Li Abstract A series of well-defined amphiphilic graft copolymers containing hydrophilic poly(acrylic acid) (PAA) backbone and hydrophobic poly(vinyl acetate) (PVAc) side chains were synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization followed by selective hydrolysis of poly(tert -butyl acrylate) backbone. A new Br-containing acrylate monomer, tert -butyl 2-((2-bromopropanoyloxy)methyl) acrylate, was first prepared, which can be polymerized via RAFT in a controlled way to obtain a well-defined homopolymer with narrow molecular weight distribution (Mw/Mn = 1.08). This homopolymer was transformed into xanthate-functionalized macromolecular chain transfer agent by reacting with o -ethyl xanthic acid potassium salt. Grafting-from strategy was employed to synthesize PtBA- g -PVAc well-defined graft copolymers with narrow molecular weight distributions (Mw/Mn < 1.40) via RAFT of vinyl acetate using macromolecular chain transfer agent. The final PAA- g -PVAc amphiphilic graft copolymers were obtained by selective acidic hydrolysis of PtBA backbone in acidic environment without affecting the side chains. The critical micelle concentrations in aqueous media were determined by fluorescence probe technique. The micelle morphologies were found to be spheres. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6032,6043, 2009 [source] Postpolymerization modification of poly(pentafluorophenyl methacrylate): Synthesis of a diverse water-soluble polymer libraryJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2009Matthew I. Gibson Abstract This article explores the feasibility of poly(pentafluorophenyl methacrylate) (PPFMA) prepared by reversible addition fragmentation chain transfer (RAFT) polymerization as a platform for the preparation of diverse libraries of functional polymers via postpolymerization modification with primary amines. Experiments with a broad range of functional amines and PPFMA precursors of different molecular weights indicated that the postpolymerization modification reaction proceeds with good to excellent conversion for a diverse variety of functional amines and is essentially independent of the PPFMA precursor molecular weight. The RAFT end group, which was well preserved throughout the polymerization, is cleaved during postpolymerization modification to generate a thiol end group that provides possibilities for further orthogonal chain-end modification reactions. The degree of postpolymerization modification can be controlled by varying the relative amount of primary amine that is used and random polymethacrylamide copolymers can be prepared via a one-pot/two-step sequential addition procedure. Cytotoxicity experiments revealed that the postpolymerization modification strategy does not lead to any additional toxicity compared with the corresponding polymer obtained via direct polymerization, which makes this approach also of interest for the synthesis of biologically active polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4332,4345, 2009 [source] Controlled/living heterogeneous radical polymerization in supercritical carbon dioxideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2009Per B. Zetterlund Abstract Supercritical carbon dioxide (scCO2) is an inexpensive and environmentally friendly medium for radical polymerizations. ScCO2 is suited for heterogeneous controlled/living radical polymerizations (CLRPs), since the monomer, initiator, and control reagents (nitroxide, etc.) are soluble, but the polymer formed is insoluble beyond a critical degree of polymerization (Jcrit). The precipitated polymer can continue growing in (only) the particle phase giving living polymer of controlled well-defined microstructure. The addition of a colloidal stabilizer gives a dispersion polymerization with well-defined colloidal particles being formed. In recent years, nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT) polymerization have all been conducted as heterogeneous polymerizations in scCO2. This Highlight reviews this recent body of work, and describes the unique characteristics of scCO2 that allows composite particle formation of unique morphology to be achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3711,3728, 2009 [source] RAFT polymerization kinetics: How long are the cross-terminating oligomers?JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2009Dominik Konkolewicz Abstract We extend a new model for the kinetics of reversible addition-fragmentation chain transfer (RAFT) polymerization. The essence of this model is that the termination of the radical intermediate formed by the RAFT process occurs only with very short oligomeric radicals. In this work, we consider cross-termination of oligomers up to two monomers and an initiator fragment. This model accounts for the absence of three-armed stars in the molecular weight distribution, which are predicted by other cross-termination models, since the short third arm makes a negligible difference to the polymer's molecular weight. The model is tested against experiments on styrene mediated by cyano-isopropyl dithiobenzoate, and ESR experiments of the intermediate radical concentration. By comparing our model to experiments, we may determine the significance of cross-termination in RAFT kinetics. Our model suggests that to agree with the known data on RAFT kinetics, the majority of cross-terminating chains are dimeric or shorter. If longer chains are considered in cross-termination reactions, then significant discrepancies with the experiments (distinguishable star polymers in the molecular weight distribution) and quantum calculations will result. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3455,3466, 2009 [source] Core-shell particles with glycopolymer shell and polynucleoside core via RAFT: From micelles to rodsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2009Samuel Pearson Abstract Amphiphilic block copolymers were synthesized via the reversible addition fragmentation chain transfer (RAFT) copolymerisation of 2-methacrylamido glucopyranose (MAG) and 5,- O -methacryloyl uridine (MAU). Homopolymerisations of both monomers using (4-cyanopentanoic acid)-4-dithiobenzoate (CPADB) proceeded with pseudo first order kinetics in a living fashion, displaying linear evolution of molecular weight with conversion and low PDIs. A bimodal molecular weight distribution was observed for PMAU at low conversions courtesy of hybrid behavior between living and conventional free radical polymerization. This effect was more pronounced when a PMAG macroRAFT agent was chain extended with MAU, however, in both cases, good control was attained once the main RAFT equilibrium was established. A stability study on PMAU found that its hydrolysis is diffusion controlled, and is accelerated at physiological pH compared with neutral conditions. Self-assembly of four block copolymers with increasing hydrophobic (PMAU) block lengths produced micelles, which demonstrated an increased tendency to form rods as the PMAU block length increased. Interestingly, none of the block copolymers were surface-active. An initial assessment of PMAU's ability to bind the nucleoside adenosine through base pairing was highly promising, with DSC measurements indicating that adenosine is fully miscible in the PMAU matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1706,1723, 2009 [source] Poly(ethylene glycol)-based amphiphilic model conetworks: Synthesis by RAFT polymerization and characterizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2008Mariliz Achilleos Abstract Poly(ethylene glycol) (PEG)-containing quasi-model amphiphilic polymer conetworks (APCNs) were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using ,,,-bis(2-cyanoprop-2-yl dithiobenzoate)-PEG as a bifunctional RAFT macrochain transfer agent (macro-CTA) and stepwise additions of a hydrophobic monomer and a crosslinker (crosslinker: macro-CTA = 10:1, reaction time 24 h). Three different types of monomers, methyl methacrylate (MMA), n -butyl acrylate and styrene, were employed as the hydrophobic monomers, whereas ethylene glycol dimethacrylate, ethylene glycol diacrylate and 1,4-divinylbenzene served as the respective crosslinkers. PEG homopolymer hydrophilic quasi-model networks were also prepared by RAFT-polymerizing the three crosslinkers directly onto the two active ends of the PEG-based macro-CTA. From the three ABA triblock copolymers prepared, the MMA-containing one was obtained at the highest polymerization yields. The crosslinking yields of the three ABA triblock copolymers with the corresponding crosslinkers were higher than those of the PEG-based macro-CTA with the same crosslinkers. The degrees of swelling (DSs) of all conetworks were measured in water and in tetrahydrofuran (THF). The DSs of the APCNs in THF were higher than those in water, whereas the reverse was true for the DSs of the hydrophilic homopolymer networks. Finally, the aqueous DSs of the APCNs were lower than those of the corresponding hydrophilic homopolymer networks. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7556,7565, 2008 [source] Branched polystyrene with abundant pendant vinyl functional groups from asymmetric divinyl monomerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2008Zhong-Min Dong Abstract Branched polystyrenes with abundant pendant vinyl functional groups were prepared via radical polymerization of an asymmetric divinyl monomer, which possesses a higher reactive styryl and a lower reactive butenyl. Employing a fast reversible addition fragmentation chain transfer (RAFT) equilibrium, the concentration of active propagation chains remained at a low value and thus crosslinking did not occur until a high level of monomer conversion. The combination of a higher reaction temperature (120 °C) and RAFT agent cumyl dithiobenzoate was demonstrated to be optimal for providing both a more highly branched architecture and a higher polymer yield. The molecular weights (Mws) increased with monomer conversions because of the controlled radical polymerization characteristic, whereas the Mw distributions broadened showing a result of the gradual increase of the degree of branching. The evolution of branched structure has been confirmed by a triple detection size exclusion chromatography (TRI-SEC) and NMR technique. Furthermore, the double bonds in the side chains were successfully used for chemical modification reactions. 1H NMR and FTIR measurements reveal that the great mass of pendant vinyl groups were converted to the corresponding objective end-groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6023,6034, 2008 [source] A strategy for synthesis of ion-bonded amphiphilic miktoarm star copolymers via supramolecular macro-RAFT agentJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2008Dairen Lu Abstract Amphiphilic supramolecular miktoarm star copolymers linked by ionic bonds with controlled molecular weight and low polydispersity have been successfully synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization using an ion-bonded macromolecular RAFT agent (macro-RAFT agent). Firstly, a new tetrafunctional initiator, dimethyl 4,6-bis(bromomethyl)-isophthalate, was synthesized and used as an initiator for atom transfer radical polymerization (ATRP) of styrene to form polystyrene (PSt) containing two ester groups at the middle of polymer chain. Then, the ester groups were converted into tertiary amino groups and the ion-bonded supramolecular macro-RAFT agent was obtained through the interaction between the tertiary amino group and 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid (DMP). Finally, ion-bonded amphiphilic miktoarm star copolymer, (PSt)2 -poly(N -isopropyl-acrylamide)2, was prepared by RAFT polymerization of N -isopropylacrylamide (NIPAM) in the presence of the supramolecular macro-RAFT agent. The polymerization kinetics was investigated and the molecular weight and the architecture of the resulting star polymers were characterized by means of 1H-NMR, FTIR, and GPC techniques. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5805,5815, 2008 [source] Simultaneous reversible addition fragmentation chain transfer and ring-opening polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2008Maude Le Hellaye Abstract The simultaneous ring-opening polymerization (ROP) of ,-caprolactone (,-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 ,-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 [source] An efficient synthesis of telechelic poly (N -isopropylacrylamides) and its application to the preparation of ,,,-dicholesteryl and ,,,-dipyrenyl polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008Florence Segui Abstract Poly(N -isopropylacrylamide)s (PNIPAMs) with cholesteryl or pyrenyl moieties at each chain end (CH-PNIPAMs or Py-PNIPAMs) were prepared via end-group modification of ,,,-dimercapto poly(N -isopropylacrylamides), ranging in molecular weight from , 7000 to 45,000 g mol,1 with a polydispersity index of 1.10 or lower. The telechelic thiol functionalized PNIPAMs were obtained by aminolysis of ,,,-di(isobutylthiocarbonylthio)-poly(N -isopropylacrylamide)s (iBu-PNIPAMs) obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization of N -isopropylacrylamide in the presence of the difunctional chain transfer agent, diethylene glycol di(2-(1-isobutyl)sulfanylthiocarbonylsulfanyl-2-methyl propionate) (DEGDIM). The self-assembly of the polymers in water was assessed by fluorescence spectroscopy, using the intrinsic emission of Py-PNIPAM or the emission of pyrene added as a probe in aqueous solutions of CH-PNIPAM. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 314,326, 2008 [source] A doubly responsive AB diblock copolymer: RAFT synthesis and aqueous solution properties of poly (N -isopropylacrylamide- block -4-vinylbenzoic acid)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2007Andrew B. Lowe Abstract We describe herein the synthesis and self-assembly characteristics of a doubly responsive AB diblock copolymer comprised of N -isopropylacrylamide (NIPAM) and 4-vinylbenzoic acid (VBZ). The AB diblock copolymer was prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization in DMF employing a trithiocarbonate-based RAFT agent. PolyNIPAM was employed as the macroRAFT agent. The NIPAM homopolymerization was shown to possess all the characteristics of a controlled process, and the blocking with VBZ was judged, by size exclusion chromatography, to be essentially quantitative. The NIPAM-VBZ block copolymer was subsequently demonstrated to be able to form normal and inverse micelles in the same aqueous solution by taking advantage of the stimuli responsive characteristics of both building blocks. Specifically, and as judged by NMR spectroscopy and dynamic light scattering, raising the temperature to 40 °C (above the lower critical solution temperature of the NIPAM block), while at pH 12 results in supramolecular self-assembly to yield nanosized species that are composed of a hydrophobic NIPAM core stabilized by a hydrophilic VBZ corona. Conversely, lowering the solution pH to 2.0 at ambient temperature results in the formation of aggregates in which the VBZ block is now hydrophobic and in the core, stabilized by the hydrophilic NIPAM block. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5864,5871, 2007 [source] | |||||||||||||||||||||||||