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Transfer Agent (transfer + agent)
Kinds of Transfer Agent Selected AbstractsUse of Hydroxyl Functionalized (Meth)acrylic Cross-Linked Polymer Microparticles as Chain Transfer Agent in Cationic Photopolymerization of Cycloaliphatic Epoxy Monomer, 1MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2003Ludovic Valette Abstract In the case of cationic-type photopolymerized epoxy networks, a new type of chain transfer agent based on hydroxyl functional acrylic cross-linked polymer microparticles (CPM, also called microgels) has been tested. The CPM functionality was obtained through hydroxyethyl acrylate (HEA) monomer, used as comonomer with butyl acrylate (BA) and hexane diol diacrylate (HDDA). Stabilizing monomers were also required for the synthesis of CPM. In order to compare their particular effects, 4 sets of CPM were synthesized with 4 different stabilizing agents, either hydroxyl functional or not. Consequently, two types of OH groups were present in the particles: primary groups coming from HEA and preferentially located in the particles, and optional hydroxyl groups due to the hydroxyl functional stabilizing agents which were mainly placed onto the particles' surface. The viscoelastic properties of the photopolymerized films have been used to obtain information about the chain transfer reaction and the network microstructure. In all cases, the rubber modulus, was improved because of the decrease of the number of dangling epoxy chains in the epoxy network. When hydroxyl groups were only present in the particles, the mobility of the linkages was assumed to be low, and the mechanical relaxation temperature, T,, strongly increased. However, CPM aggregation occurred at high CPM concentrations, lowering and T,. On the contrary, when OH groups were located both on the surface as well as inside the particles, no large CPM aggregation took place, even with [CPM],=,40 wt.-%. Nevertheless, the presumably higher mobility of the linkages on the particles' surface prevented any T, increase. The water absorption of all systems based on CPM was very low, around 2% whatever the concentration of chain transfer agent. Schematic description of the transfer reaction between a propagating cationic-type epoxy chain and a hydroxyl functional CPM. [source] Radical Telomerisation of Vinyl Phosphonic Acid with a Series of Chain Transfer AgentsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2007Ghislain David Abstract The use of CTAs for the radical polymerisation of VPA has been successfully applied for the first time. Several CTAs were investigated, including thiol, disulfide and halogenated compounds. The use of mercaptoacetic acid led to the synthesis of the mercaptan VPA monoadduct, which was attributed to a high transfer constant (CT,=,ktr/kp) of approximately 7. Transfer reactions with VPA appeared to be unsuccessful when using benzyldisulfide, 1,1,1-trichloroethane and trichloroacetic acid. Application of bromotrichloromethane as a transfer agent led to the oligomerisation of VPA, with final conversion being approximately 80%. The transfer events were characterised by 13C NMR, MALDI-TOF and elemental analysis. Molecular weights of the successful VPA polymerisations showed values ranging from 600 to 5,000 g,·,mol,1, which were in close agreement with the theoretically calculated values. [source] Preparation of high cis -1,4 polyisoprene with narrow molecular weight distribution via coordinative chain transfer polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2010Changliang Fan Abstract High cis -1,4 polyisoprene with narrow molecular weight distribution has been prepared via coordinative chain transfer polymerization (CCTP) using a homogeneous rare earth catalyst composed of neodymium versatate (Nd(vers)3), dimethyldichlorosilane (Me2SiCl2), and diisobutylaluminum hydride (Al(i -Bu)2H) which has strong chain transfer affinity is used as both cocatalyst and chain transfer agent (CTA). Differentiating from the typical chain shuttling polymerization where dual-catalysts/CSA system has been used, one catalyst/CTA system is used in this work, and the growing chain swapping between the identical active sites leads to the formation of high cis -1,4 polyisoprene with narrowly distributed molecular weight. Sequential polymerization proves that irreversible chain termination reactions are negligible. Much smaller molecular weight of polymer obtained than that of stoichiometrically calculated illuminates that, differentiating from the typical living polymerization, several polymer chains can be produced by one neodymium atom. The effectiveness of Al(i -Bu)2H as a CTA is further testified by much broad molecular weight distribution of polymer when triisobutylaluminum (Al(i -Bu)3), a much weaker chain transfer agent, is used as cocatalyst instead of Al(i -Bu)2H. Finally, CCTP polymerization mechanism is validated by continuously decreased Mw/Mn value of polymer when increasing concentration of Al(i -Bu)2H extra added in the Nd(ver)3/Me2SiCl2/Al(i -Bu)3 catalyst system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [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] Kinetic investigation of the RAFT polymerization of p -acetoxystyreneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2010Solène I. Cauët Abstract The kinetics of the RAFT polymerization of p -acetoxystyrene using a trithiocarbonate chain transfer agent, S -1-dodecyl- S,-(,,,,-dimethyl-,,-acetic acid)trithiocarbonate, DDMAT, was investigated. Parameters including temperature, percentage initiator, concentration, monomer-to-chain transfer agent ratio, and solvent were varied and their impact on the rate of polymerization and quality of the final polymer examined. Linear kinetic plots, linear increase of Mn with monomer conversion, and low final molecular weight dispersities were used as criteria for the selection of optimized polymerization conditions, which included a temperature of 70 or 80 °C with 10 mol % AIBN initiator in bulk for low conversions or in 1,4-dioxane at a monomer-to-solvent volume ratio of 1:1 for higher conversions This study opens the way for the use of DDMAT as a chain transfer agent for RAFT polymerization to incorporate p -acetoxystyrene together with other functional monomers into well-defined copolymers, block copolymers, and nanostructures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2517,2524, 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] 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] Novel well-defined glycopolymers synthesized via the reversible addition fragmentation chain transfer process in aqueous mediaJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2009Zhicheng Deng Abstract We describe here the direct synthesis of novel gluconamidoalkyl methacrylamides by reacting D -gluconolactone with aminoalkyl methacrylamides. The glycomonomers were then successfully polymerized via the reversible addition-fragmentation chain transfer process (RAFT) using 4-cyanopentanoic acid dithiobenzoate (CTP) as chain transfer agent and 4,4,-azobis(4-cyanovaleric acid) (ACVA) as the initiator in aqueous media. Well-defined polymers were obtained as revealed by gel permeation chromatography. Diblock copolymers were then synthesized by the macro-CTA approach. The cationic glycopolymers were subsequently used in the formation of nanostructures via the complexation with plasmid DNA. As noted by dynamic light scattering, monodisperse nanoparticles were obtained via the electrostatic interaction of the cationic glycopolymer with DNA. The sizes of the nanoparticles formed were found to be stable and independent of pH. In vitro cell viability studies of the glycopolymers were carried out using HELA cell lines. The RAFT synthesized glycopolymers and cationic glyco-copolymers revealed to be nontoxic. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 614,627, 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] 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] Copolymerizations of butyl methacrylate and fluorinated methacrylates via RAFT miniemulsion polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2007Tian-Ying Guo Abstract Copolymerizations of n -butyl methacrylate (BMA) and fluoro-methacrylates (including 2,2,3,4,4,4-hexafluorobutyl methacrylate, HFBMA and 2,2,2-trifluoroethyl methacrylate, TFEMA) were carried out via reversible addition-fragmentation chain transfer miniemulsion polymerization, using cumyl dithiobenzoate as a chain transfer agent. The experimental results show that the copolymerizations exhibit "living" fashion, with controlled molecular weights and narrow polydispersities. The reactivity ratios of BMA and fluoromethacrylate in this kind of polymerization system were investigated by size exclusion chromatography and nuclear magnetic resonance, from which the Q - and e -values of HFBMA and TFEMA were calculated. Compared with its corresponding non-fluoric methacrylate, fluorinated methacrylate exhibits higher resonance stability of the radical adducts. The Q -value of fluorinated methacrylate is higher (QBMA = 0.82 to QHFBMA = 1.70 and QEMA = 0.76 to QTFEMA = 1.01), and e -value is much larger (eBMA = 0.28 to eHFBMA = 1.24 to and eEMA = 0.17 to eTFEMA = 1.29) for its rather unique high electron-withdrawing inductive effect of the fluoroalkyl ester group. The thermal property and the wetting property of copolymers were also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5067,5075, 2007 [source] RAFT polymerization of styrenic-based phosphonium monomers and a new family of well-defined statistical and block polyampholytesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2007Ran Wang Abstract We describe herein the first example of the controlled reversible addition-fragmentation chain transfer (RAFT) radical homo- and copolymerization of phosphonium-based styrenic monomers mediated with a trithiocarbonate-based RAFT chain transfer agent (CTA) directly in aqueous media. In the case of homopolymer syntheses the polymerizations proceed in a controlled fashion yielding materials with predetermined molecular characteristics as evidenced from the narrow molecular mass distributions (MMD) and the excellent agreement between the theoretical and experimentally determined molecular masses (MM). We also demonstrate the controlled nature of the homopolymerization of 4-vinylbenzoic acid with the same CTA in DMSO. We subsequently prepared both statistical and block copolymers from the phosphonium/4-vinylbenzoic acid monomers to yield the first examples of polyampholytes in which the cationic functional group is a quaternary phosphonium species. We show that the kinetic characteristics of the statistical copolymerizations are different from the homopolymerizations and proceed, generally, at a significantly faster rate although there appears to be a composition dependence on the rate. Given the inherent problems in characterizing such polyampholytic copolymers via aqueous size exclusion chromatography we have qualitatively proved their successful formation via FTIR spectroscopy. Finally, in a preliminary experiment we qualitatively demonstrate the ability of such pH-responsive block copolymers to undergo supramolecular self-assembly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2468,2483, 2007 [source] Dendrimer-star polymer and block copolymer prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization with dendritic chain transfer agentJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2005Chun-Yan Hong Abstract 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 [source] Synthesis of telechelic oligomers by atom transfer radical polymerization: A study of acrylate monomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2005Belkacem Otazaghine Abstract Different acrylate oligomers were synthesized by atom transfer radical polymerization in the presence of a transfer agent and CuBr/1,1,4,7,10,10-hexamethyltriethylenetetramine. The functionality in bromine was determined by 1H NMR. These oligomers were coupled in the presence of Cu(0) and the ligand 2,2,-bipyridine. The coupling yield was determined by size exclusion chromatography and NMR analysis and depended on the nature of the monomer and not on the molecular weight. In other words, the preliminary functionalization of the brominated chain end with styrene increased the coupling yield. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2377-2394, 2005 [source] Synthesis of ethylene/propylene elastomers containing a terminal reactive group: The combination of metallocene catalysis and control chain transfer reactionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005U. Kandil Abstract This article discusses a chemical route to prepare new ethylene/propylene copolymers (EP) containing a terminal reactive group, such as ,-CH3 and OH. The chemistry involves metallocene-mediated ethylene/propylene copolymerization in the presence of a consecutive chain transfer agent,a mixture of hydrogen and styrene derivatives carrying a CH3 (p -MS) or a silane-protected OH (St-OSi). The major challenge is to find suitable reaction conditions that can simultaneously carry out effective ethylene/propylene copolymerization and incorporation of the styrenic molecule (St-f) at the polymer chain end, in other words, altering the St-f incorporation mode from copolymerization to chain transfer. A systematic study was conducted to examine several metallocene catalyst systems and reaction conditions. Both [(C5Me4)SiMe2N(t -Bu)]TiCl2 and rac-Et(Ind)2ZrCl2, under certain H2 pressures, were found to be suitable catalyst systems to perform the combined task. A broad range of St-f terminated EP copolymers (EP- t -p-MS and EP- t -St-OH), with various compositions and molecular weights, have been prepared with polymer molecular weight inversely proportional to the molar ratio of [St-f]/[monomer]. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1858,1872, 2005 [source] Radical Telomerisation of Vinyl Phosphonic Acid with a Series of Chain Transfer AgentsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2007Ghislain David Abstract The use of CTAs for the radical polymerisation of VPA has been successfully applied for the first time. Several CTAs were investigated, including thiol, disulfide and halogenated compounds. The use of mercaptoacetic acid led to the synthesis of the mercaptan VPA monoadduct, which was attributed to a high transfer constant (CT,=,ktr/kp) of approximately 7. Transfer reactions with VPA appeared to be unsuccessful when using benzyldisulfide, 1,1,1-trichloroethane and trichloroacetic acid. Application of bromotrichloromethane as a transfer agent led to the oligomerisation of VPA, with final conversion being approximately 80%. The transfer events were characterised by 13C NMR, MALDI-TOF and elemental analysis. Molecular weights of the successful VPA polymerisations showed values ranging from 600 to 5,000 g,·,mol,1, which were in close agreement with the theoretically calculated values. [source] Atom-Transfer Radical Polymerization: A Strategy for the Synthesis of Halogen-Free Amino-Functionalized Poly(methyl methacrylate) in a One-Pot ReactionMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2004Veera Bhadraiah Sadhu Abstract Summary: An initiator containing an alkyl bromide unit and a protected amine functional group is used with CuBr/N,N,N,,N,,N,-pentamethyldiethylenetriamine (PMDETA), in a 1:2 molar ratio with respect to initiator concentration, in order to obtain amino-group terminated as well as halogen-free poly(methyl methacrylate) (PMMA) in a one-pot atom-transfer radical polymerization (ATRP). The terminal bromines are replaced by hydrogen atoms of the PMDETA ligand, which acts as a transfer agent. However, terminating side reactions like disproportionation or dehydrobromination occur from the beginning of the polymerization. Kinetic studies by in-line Raman spectroscopy and off-line 1H NMR spectroscopy revealed that the controlled character of the ATRP is lost under these conditions. The measured molecular weights were consistently higher than the theoretical ones and the molecular weight distributions are relatively broad. Thermal analysis of the obtained poly(methyl methacrylate) shows two main degradation steps, one starting from unsaturated end groups (depolymerization), and one caused by main-chain scission, a further proof for the occurrence of terminating side reactions. Structural analysis of PMMA by matrix-assisted laser desorption-ionization mass spectrometry. [source] Use of Hydroxyl Functionalized (Meth)acrylic Cross-Linked Polymer Microparticles as Chain Transfer Agent in Cationic Photopolymerization of Cycloaliphatic Epoxy Monomer, 1MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2003Ludovic Valette Abstract In the case of cationic-type photopolymerized epoxy networks, a new type of chain transfer agent based on hydroxyl functional acrylic cross-linked polymer microparticles (CPM, also called microgels) has been tested. The CPM functionality was obtained through hydroxyethyl acrylate (HEA) monomer, used as comonomer with butyl acrylate (BA) and hexane diol diacrylate (HDDA). Stabilizing monomers were also required for the synthesis of CPM. In order to compare their particular effects, 4 sets of CPM were synthesized with 4 different stabilizing agents, either hydroxyl functional or not. Consequently, two types of OH groups were present in the particles: primary groups coming from HEA and preferentially located in the particles, and optional hydroxyl groups due to the hydroxyl functional stabilizing agents which were mainly placed onto the particles' surface. The viscoelastic properties of the photopolymerized films have been used to obtain information about the chain transfer reaction and the network microstructure. In all cases, the rubber modulus, was improved because of the decrease of the number of dangling epoxy chains in the epoxy network. When hydroxyl groups were only present in the particles, the mobility of the linkages was assumed to be low, and the mechanical relaxation temperature, T,, strongly increased. However, CPM aggregation occurred at high CPM concentrations, lowering and T,. On the contrary, when OH groups were located both on the surface as well as inside the particles, no large CPM aggregation took place, even with [CPM],=,40 wt.-%. Nevertheless, the presumably higher mobility of the linkages on the particles' surface prevented any T, increase. The water absorption of all systems based on CPM was very low, around 2% whatever the concentration of chain transfer agent. Schematic description of the transfer reaction between a propagating cationic-type epoxy chain and a hydroxyl functional CPM. [source] Synthesis of Poly(glycidyl methacrylate)- block -Poly(pentafluorostyrene) by RAFT: Precursor to Novel Amphiphilic Poly(glyceryl methacrylate)- block -Poly(pentafluorostyrene)MACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2008Chakravarthy S. Gudipati Abstract Poly(glycidyl methacrylate) (PGMA) was synthesized by the RAFT method in the presence of 2-cyanoprop-2-yl dithiobenzoate (CPDB) chain transfer agent using different [GMA]/[CPDB] molar ratios. The living radical polymerization resulted in controlled molecular weights and narrow polydispersity indices (PDI) of ,1.1. The polymerization of pentafluorostyrene (PFS) with PGMA as the macro-RAFT agent yielded narrow PDIs of ,1.2 at 60,°C and ,1.5 at 80,°C. The epoxy groups of the PGMA block were hydrolyzed to obtain novel amphiphilic copolymer, poly(glyceryl methacrylate)- block -poly(pentafluorostyrene) [PGMA(OH)- b -PPFS]. The PGMA epoxy group hydrolysis was confirmed by 1H NMR and FTIR spectroscopy. DSC investigation revealed that the PGMA- b -PPFS polymer was amorphous while the PGMA(OH)- b -PPFS displayed a high degree of crystallinity. [source] Simultaneous Controllability of PSD and MWD in Emulsion PolymerisationMACROMOLECULAR REACTION ENGINEERING, Issue 5 2008Stephen J. Sweetman Abstract A sensitivity study of particle size distribution (PSD) and molecular weight distribution (MWD) responses to perturbations in initiator, surfactant, monomer and chain transfer agent in a semi-batch emulsion polymerisation is presented. The objective is to provide a systematic study on the ability to simultaneously control both PSD and MWD, towards inferential control of end-use product properties. This would lead towards identification of the practical feasible regions of operability. All inputs appeared to have an intrinsic and simultaneous influence on end-time PSD and MWD. Trends shown in experimental results have been explained in a mechanistic sense and also compared to simulation results from a combined PSD/MWD population balance model. The preliminary comparison between experiment and simulation highlights areas to be focussed on with respect to model improvement. [source] The Role of Allylanisole in Metallocene-Catalyzed Propylene Polymerization and Synthesis of End-Capped OligomersMACROMOLECULAR REACTION ENGINEERING, Issue 4 2008Muhammad Atiqullah Propylene was copolymerized with allylanisole (AA) using Me2Si(Ind)2ZrCl2 and Et(Ind)2ZrCl2, and the methylaluminoxane MAO cocatalyst at 70,°C and a cocatalyst to catalyst (Al:Zr) molar ratio of 1,000. It was fed at 8.5 bar(g). The weight-average molecular weight, , for both metallocenes decreased as the AA feed concentration increased. Therefore, allylanisole acted as an in situ chain transfer agent. The chain transfer constants, ktr/kp, of AA for Et(Ind)2ZrCl2 and Me2Si(Ind)2ZrCl2 turned out to be 0.33 and 0.40, respectively. The characterization of the resulting products by 1H NMR demonstrated that AA end-capped the isotactic poly(propylene) chains which showed to be low molecular weight oligomers; 4.96,×,103,,,,,,9.80,×,103. An appropriate chain transfer mechanism for AA has been proposed. [source] Model Development in Thermal Styrene PolymerizationMACROMOLECULAR SYMPOSIA, Issue 1 2007Bryan Matthews Abstract Summary: The thermal polymerization of styrene is usually modeled by relying on a reaction scheme and a set of equations that were developed more than three decades ago by Hui and Hamielec. Many detailed models of styrene polymerization are available in the open literature and they are mostly based on the work of Hui and Hamielec, which nearly makes this the standard to follow in explaining the behavior of polystyrene reactors. The model of Hui and Hamielec does a very nice job of describing monomer conversion data but discrepancies are seen between observed and predicted values of number and weight average molecular weights, Mn and Mw. Discrepancies in number average molecular weight seem to be the result of random noise. Discrepancies in weight average molecular weight grow as the polymerization temperature decreases and some of the trends observed in the residuals over the entire temperature range cannot be attributed to random noise. Hui and Hamielec attributed the observed deficiencies to a standard deviation of ±10% in their GPC measurements. A new data set with an experimental error of 2% for average molecular weights is presented. The set contains measured values of Mn, Mw and Mz, so the polymerization scheme has been extended to include third order moments. The data set also includes the effect of ethylbenzene as a chain transfer agent. We present the results of comparing model predictions to our measurements and the adjustments made in the original set of kinetic parameters published by Hui and Hamielec. [source] Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and DienesMACROMOLECULAR SYMPOSIA, Issue 1 2004Alain Deffieux Abstract The influence of MgR2 and AlR3 additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s-Bu2Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4- to 1,2- chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R3Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed. Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators. [source] Evaluation of the interfacial state in high impact polystyrene through dynamic mechanical analysis as a function of the synthesis conditions,POLYMER ENGINEERING & SCIENCE, Issue 11 2007R. Díaz de León High impact polystyrene was synthesized using two series of styrene/butadiene (SB) tapered block copolymers with a polystyrene (PS)/polybutadiene (PB) composition of 30/70 and 10/90 wt%. During the synthesis, concentration of initiator, SB and transfer agent were varied. From dynamic mechanical analysis, the corresponding , relaxation of the rubber phase was detected at low temperature (near ,100°C) and that of the glassy PS phase at high temperature (near 100°C). Also, another relaxation at temperature near 40°C was identified, which was associated to the , relaxation of the glassy PS phase. The variations found in the , relaxation of the rubber phase, were attributed to changes in the morphological structure as a consequence of variation in initiator, SB or transfer agent concentrations and in SB composition. , relaxation showed a strong dependency with the interfacial state between the rubber and the glassy phase, where an increase in the amount of graft PS at the interface, which promotes the interfacial adhesion between phases, causes an increase in the magnitude of , relaxation of the PS phase. The results were attributed to variations in the interfacial area as a result of the change in the particle size and to the contribution of molecular chains of each phase in participating in the relaxation process. POLYM. ENG. SCI., 47:1827,1838, 2007. © 2007 Society of Plastics Engineers [source] Telomerization of acrylic acid with mercaptans: Part 2.POLYMER INTERNATIONAL, Issue 4 2001Kinetics of the synthesis of star-shaped macromolecules of acrylic acid Abstract The telomerization of acrylic acid with a polyfunctional transfer agent initiated by 2,2,-azobisisobutyronitrile, was first investigated in an organic medium (THF) at 65,°C. Transfer constants (CT) for three mercaptans, ethylene glycol bisthioglycolate, trimethylolpropane tris(2-mercaptoacetate) and pentaerythritol tetrakis(3-mercaptopropionate) of about 6.1, 6.3 and 7.3, respectively, were determined. From these results, it followed that a well-defined star poly(acrylic acid) could not be synthesized via telomerization of acrylic acid in THF. Nevertheless, the same study was performed with the tetrafunctional transfer agent in water/THF mixtures. This work emphasized that the nature of the solvent plays an important role in determining the transfer constant. Thus, the value of CT for the tetrafunctional transfer agent decreased from 7.3 in THF to 1, the ,ideal' case for telomerization (CT,,,1), for the mixture of solvents water/THF (80%, 20%, v/v). With this route, it seems that acrylic acid star-shaped macromolecules could be synthesized via telomerization. © 2001 Society of Chemical Industry [source] One-Pot Synthesis of Lactide,Styrene Diblock Copolymers via Catalytic Immortal Ring-Opening Polymerization of Lactide and Nitroxide-Mediated Polymerization of StyreneCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 5 2010Valentin Poirier Abstract An efficient, practical, and industrially relevant procedure for the production of polymer materials, in which a part of the oil-derived polyolefins has been replaced by a renewable, biodegradable, and biocompatible poly(lactide) block, is presented. Binary catalytic systems combining innocuous metals (yttrium, zinc, magnesium, or calcium) and bifunctional alcohols (acting as transfer agents) were developed to promote the immortal ring-opening polymerization of lactide directly in styrene. Up to 20,000,equivalents of lactide were polymerized (metal catalyst loading of 50,100,ppm) in a controlled fashion in the presence of 10,100,equivalents of a double-headed transfer agent to give as many end-functionalized poly(lactide) macromolecules that can be used eventually as macroinitiators for the controlled nitroxide-mediated polymerization of styrene. The specific use of the sterically shielded complex [BDI- iPr]Zn-N(SiMe3)2 ([BDI- iPr]=bis(diketiminate) ligand) allowed the efficient, catalytic, and controlled production of poly(lactide)- block -poly(styrene) materials in a one-pot, solvent-free sequential procedure, with nearly 100,% atom-efficiency. [source] Perfluorocyclobutyl-containing Amphiphilic Block Copolymers Synthesized by RAFT PolymerizationCHINESE JOURNAL OF CHEMISTRY, Issue 11 2009Yongjun Chen Abstract Amphiphilic block copolymers containing hydrophobic perfluorocyclobutyl-based (PFCB) polyacrylate and hydrophilic poly(ethylene glycol) (PEG) segments were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. The PFCB-containing acrylate monomer, p -(2-(p -tolyloxy)perfluorocyclobutoxy)-phenyl acrylate, was first synthesized from commercially available compounds in good yields, and this kind of acrylate monomer can be homopolymerized by free radical polymerization or RAFT polymerization. Kinetic study showed the 2,2,-azobis(isobutyronitrile) (AIBN) initiated and cumyl dithiobenzoate (CDB) mediated RAFT polymerization was in a living fashion, as suggested by the fact that the number-average molecular weights (Mn) increased linearly with the conversions of the monomer, while the polydispersity indices kept less than 1.10. The block polymers with narrow molecular weight distributions (Mw/Mn,1.21) were prepared through RAFT polymerization using PEG monomethyl ether capped with 4-cyanopentanoic acid dithiobenzoate end group as the macro chain transfer agent (mPEG-CTA). The length of the hydrophobic segment can be tuned by the feed ratio of the PFCB-based acrylate monomer and the extending of the polymerization time. The micellization behavior of the block copolymers in aqueous media was investigated by the fluorescence probe technique. [source] Electrospray mass spectra of group 6 (Fischer) carbenes in the presence of electron-donor compoundsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2003M. A. Sierra Abstract Fischer carbene complexes 1,7 are not ionized under standard electrospray ionization (ESI) conditions. We report here that unsaturated chromium and tungsten (Fischer) carbene complexes can be ionized in an electrospray ion source in the presence of electron-donor compounds such as hydroquinone (HQ) or tetrathiafulvalene (TTF). The addition of these compounds, which seem to act as electron transfer agents, permits the recording and study of their ESI mass spectra in the negative mode of detection. Both chromium and tungsten(0) carbene complexes undergo in the first fragmentation stage a double simultaneous decarbonylation process. Copyright © 2003 John Wiley & Sons, Ltd. [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] Dendrimers as scaffolds for multifunctional reversible addition,fragmentation chain transfer agents: Syntheses and polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004Xiaojuan Hao Abstract The synthesis and characterization of novel first- and second-generation true dendritic reversible addition,fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3-benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z-group architecture based on 1,1,1-hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1.3 for PS) via bulk free-radical polymerization at 60 °C. The novel dendrimer-based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number-average molecular weight (Mn) with the monomer,polymer conversion, yielding star polymers with molecular weights of up to Mn = 160,000 g mol,1 for PBA (based on a linear PBA calibration) and up to Mn = 70,000 g mol,1 for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1-hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star-shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star-shaped polymeric materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5877,5890, 2004 [source] | |||||||||||||