The Experts below are selected from a list of 1503 Experts worldwide ranked by ideXlab platform
Christopher Barnerkowollik - One of the best experts on this subject based on the ideXlab platform.
-
photo induced ligation of acrylonitrile butadiene rubber selective tetrazole ene coupling of chain end functionalized copolymers of 1 3 butadiene
Macromolecules, 2013Co-Authors: Christoph J Durr, Paul Lederhose, Lebohang Hlalele, Doris Abt, Andreas Kaiser, Sven Brandau, Christopher BarnerkowollikAbstract:A highly selective photo-induced nitrile imine mediated tetrazole–ene coupling (NITEC) of chain-end-functionalized nitrile–butadiene rubber (NBR) is reported, providing nitrile rubbers with molar masses of up to 48 000 g·mol–1. NBR was obtained via the reversible addition–fragmentation chain transfer (RAFT) mediated copolymerization of acrylonitrile and 1,3-butadiene employing a novel photoreactive tetrazole-functionalized Trithiocarbonate. The herein reported tetrazole-functionalized Trithiocarbonate represents—to the best of our knowledge—the first ever reported photoreactive RAFT agent capable of undergoing light-induced ligations with enes. Molar masses of the tetrazole-functionalized NBRs were in the range of 1000 to 38 000 g·mol–1 with dispersities between 1.1 to 1.6. By an appropriate choice of the tetrazole substituents, a reaction of the in situ formed enophile with the double bonds or the nitrile moieties of the incorporated monomer units within the polymer backbone—present in high excess relati...
-
photoinduced conjugation of dithioester and Trithiocarbonate functional raft polymers with alkenes
Macromolecules, 2011Co-Authors: Till Gruendling, Michael Kaupp, James P Blinco, Christopher BarnerkowollikAbstract:We report the photoinduced conjugation of polymers synthesized via reversible addition−fragmentation chain transfer (RAFT) polymerization with a number of low molecular weight (functional) olefins. Upon irradiation of a solution of an aliphatic alkene and the benzyl dithioacetic acid ester (CPDA) or dodecyl Trithiocarbonate (DoPAT) functional poly(alkyl acrylate) at the absorption wavelength of the thiocarbonyl group (315 nm), incorporation of the alkene at the polymer chain-end occurred. The most efficient systems identified with regard to the rate of reaction and yield were poly(butyl acrylate)/CPDA/ethyl vinyl ether (78% monoinsertion product after 1 h) and poly(butyl acrylate)/CPDA/1-pentene (73% insertion product after 7 h) at ambient temperature. An in-depth analysis of the reaction mechanism by 1H NMR and online size-exclusion chromatography-electrospray ionization tandem mass spectrometry (SEC/ESI−MSn) revealed that a possible [2 + 2] photoaddition mechanism of conjugation does not take place. Ins...
-
facile conversion of raft polymers into hydroxyl functional polymers a detailed investigation of variable monomer and raft agent combinations
Polymer Chemistry, 2010Co-Authors: Mathias Dietrich, Mathias Glassner, Till Gruendling, Christina Schmid, Jana Falkenhagen, Christopher BarnerkowollikAbstract:We report the systematic investigation of a recently introduced one-pot radical transformation of methacrylate and acrylate-type polymers prepared via reversible addition fragmentation chain transfer (RAFT) polymerization into hydroxyl functional polymers. The simple reaction procedure involves stirring a solution of the RAFT functional polymer and an azo-initiator in tetrahydrofuran at elevated temperatures (T = 60 °C) in the presence of ambient air. Subsequent reduction of the formed hydroperoxide functional polymers to hydroxyl functional polymers is achieved in a one-pot procedure using triphenylphosphine. Polymers investigated in the current study are poly(methyl acrylate) (pMA), poly(butyl acrylate) (pBA), poly(isobornyl acrylate) (piBoA) and poly(tert-butyl acrylate) (ptBA) carrying a dithiobenzoate or phenyldithioacetate end terminius as well as a symmetrical Trithiocarbonate mid chain function. Quantitative conversion into the hydroperoxyl and hydroxyl terminated product is observed when Trithiocarbonate functional polymers are employed. In the case of dithiobenzoate and phenyldithioacetate functional acrylic polymers, some minor side products due to the oxidation of the RAFT end-group are generated. Size exclusion chromatography (SEC) and size exclusion chromatography–electrospray mass spectrometry (SEC-ESI-MS) were employed to monitor the progress of the reaction and to investigate the proposed reaction mechanism for the model polymers. When Trithiocarbonate functional polymers are employed in the transformation reaction, the SEC analysis shows a bisection of the initial Mn. Collision induced dissociation (CID) MS experiments of the intermediate reaction products were conducted to gain in-depth information about the chemical structure. The new backbone linked hydroxyl group provides a versatile anchor for chemical end-group conversions and conjugation reactions with RAFT prepared polymers, alleviating problems with the rather limited ability of the dithioester end-group to undergo non-radical transformations.
-
controlled living ring closing cyclopolymerization of diallyldimethylammonium chloride via the reversible addition fragmentation chain transfer process
Macromolecules, 2007Co-Authors: Yasser Assem, Christopher Barnerkowollik, Hugh Chaffeymillar, Gerhard Wegner, Seema AgarwalAbstract:For the first time, controlled/living free-radical polymerization of a cyclopolymerizing monomer, that is diallyldimethylammonium chloride (DADMAC), was achieved via reversible addition fragmentation chain transfer (RAFT) chemistry in the presence of both Trithiocarbonate and xanthate RAFT/macromolecular design via the interchange of xanthate (MADIX) agents in aqueous solution at 60, 80, and 90 °C. The structural characterization of the polymers was achieved via nuclear magnetic resonance spectrometry, indicating that during the RAFT polymerization of DADMAC, identical to its equivalent conventional free radical polymerization, five-membered rings are formed almost exclusively. In the case of the Trithiocarbonate agent, there was excellent agreement between the theoretical and experimental number average molecular weights, Mn, with narrow polydispersities (approaching polydispersity index (PDI) ≈ 1.10) being observed (2100 g mol-1 < Mn < 51 000 g mol-1). Chain extension was carried out by sequential batch...
-
controlled living ring closing cyclopolymerization of diallyldimethylammonium chloride via the reversible addition fragmentation chain transfer process
Institute for Future Environments; Science & Engineering Faculty, 2007Co-Authors: Yasser Assem, Christopher Barnerkowollik, Hugh Chaffeymillar, Gerhard Wegner, Seema AgarwalAbstract:For the first time, controlled/living free-radical polymerization of a cyclopolymerizing monomer, that is diallyldimethylammonium chloride (DADMAC), was achieved via reversible addition fragmentation chain transfer (RAFT) chemistry in the presence of both Trithiocarbonate and xanthate RAFT/macromolecular design via the interchange of xanthate (MADIX) agents in aqueous solution at 60, 80, and 90 °C. The structural characterization of the polymers was achieved via nuclear magnetic resonance spectrometry, indicating that during the RAFT polymerization of DADMAC, identical to its equivalent conventional free radical polymerization, five-membered rings are formed almost exclusively. In the case of the Trithiocarbonate agent, there was excellent agreement between the theoretical and experimental number average molecular weights, Mn, with narrow polydispersities (approaching polydispersity index (PDI) ≈ 1.10) being observed (2100 g mol-1 < Mn < 51 000 g mol-1). Chain extension was carried out by sequential batchwise addition of the monomer, confirming the living character of the system. However, the increase in Mn with respect to conversion was not linear in the case of the xanthate agent, yet the PDIs were as low as 1.12, indicating that control was achieved. The inclusion of NaCl into the reaction mixture reduces of the rate of polymerization for both RAFT agents. Such an observation supports the hypothesis that electrostatic repulsion is crucial to fragmentation of the primary propagating radicals from the adduct RAFT radical; that is, it appears that an electrostatic interaction is affecting the (chemical) RAFT equilibrium. © 2007 American Chemical Society.
Martina H Stenzel - One of the best experts on this subject based on the ideXlab platform.
-
shell cross linked vesicles synthesized from block copolymers of poly d l lactide and poly n isopropyl acrylamide as thermoresponsive nanocontainers
Langmuir, 2004Co-Authors: Michelle Hales, Thomas P Davis, Christopher Barnerkowollik, Martina H StenzelAbstract:A polylactide (D,L-PLA) macroRAFT agent was prepared by utilizing a hydroxyl-functional Trithiocarbonate as a coinitiator for the ring-opening polymerization. The length of the resultant polymer was controlled by the concentration of the coinitiator leading to the formation of two PLA polymers with M(n) = 12500 g mol(-)(1) (PDI = 1.46) and M(n) = 20500 g mol(-)(1) (PDI = 1.38) each with omega-Trithiocarbonate functionality. Chain extension of PLA via the RAFT (free radical) polymerization of N-isopropyl acrylamide (NIPAAm) resulted in the formation of amphiphilic block copolymers with the PNIPAAm block increasing in size with conversion. TEM measurements of the aggregates obtained by self-organization of the block copolymers in aqueous solutions indicated the formation of vesicles. The sizes of these aggregates were influenced by the ratio of both blocks and the molecular weight of each block. The lower critical solution temperature (LCST) of the block copolymer was largely unaffected by the size of each block. UV turbidity measurements indicated a higher LCST for the block copolymers than for the corresponding PNIPAAm homopolymers. Stabilization of the vesicles was attained by a cross-linking chain extension of the PNIPAAm block using hexamethylene diacrylate. As the Trithiocarbonate group was located between the PLA and PNIPAAm blocks, the chain extension resulted in a cross-linked layer between the core and corona of the vesicles.
-
Shell-cross-linked vesicles synthesized from block copolymers of poly(D,L-lactide) and poly(N-isopropyl acrylamide) as thermoresponsive nanocontainers
Langmuir, 2004Co-Authors: Michelle Hales, Thomas P Davis, Christopher Barner-kowollik, Martina H StenzelAbstract:A polylactide (D,L-PLA) macroRAFT agent was prepared by utilizing a hydroxyl-functional Trithiocarbonate as a coinitiator for the ring-opening polymerization. The length of the resultant polymer was controlled by the concentration of the coinitiator leading to the formation of two PLA polymers with Mn = 12500 g mol-1 (PDI = 1.46) and Mn = 20500 g mol-1 (PDI = 1.38) each with ω-Trithiocarbonate functionality. Chain extension of PLA via the RAFT (free radical) polymerization of N-isopropyl acrylamide (NIPAAm) resulted in the formation of amphiphilic block copolymers with the PNIPAAm block increasing in size with conversion. TEM measurements of the aggregates obtained by self-organization of the block copolymers in aqueous solutions indicated the formation of vesicles. The sizes of these aggregates were influenced by the ratio of both blocks and the molecular weight of each block. The lower critical solution temperature (LCST) of the block copolymer was largely unaffected by the size of each block. UV turbidity measurements indicated a higher LCST for the block copolymers than for the corresponding PNIPAAm homopolymers. Stabilization of the vesicles was attained by a cross-linking chain extension of the PNIPAAm block using hexamethylene diacrylate. As the Trithiocarbonate group was located between the PLA and PNIPAAm blocks, the chain extension resulted in a cross-linked layer between the core and corona of the vesicles.
-
star polymer synthesis using Trithiocarbonate functional β cyclodextrin cores reversible addition fragmentation chain transfer polymerization
Journal of Polymer Science Part A, 2002Co-Authors: Martina H Stenzel, Thomas P DavisAbstract:Polystyrene stars were synthesized with reversible addition-fragmentation chain-transfer (RAFT) polymerization. The core of the stars comprised a Trithiocarbonate heptafunctional beta-cyclodextrin ring. Polymerizations were performed at 100 and 120 degreesC in the absence of an extraneous initiator and at 60 degreesC in the presence of a radical initiator. Monofunctional Trithiocarbonate was also synthesized and used to make linear polystyrene to allow direct a comparison with the star synthesis. In all cases, the polymerization kinetics conformed to pseudo-first-order behavior. The measured molecular weights of the stars were found to deviate from those predicted on the basis of the monomer/Trithiocarbonate group ratio. The extent of this deviation was dependent on the polymerization temperature, RAFT agent concentration, and conversion. Despite the low radical concentrations, termination reactions are suggested to play a significant role in the seven-arm polystyrene star syntheses. The synthetic method was found to be suitable for generating star block structures. (C) 2002 Wiley Periodicals, Inc.
-
star polymer synthesis using Trithiocarbonate functional β cyclodextrin cores reversible addition fragmentation chain transfer polymerization
Journal of Polymer Science Part A, 2002Co-Authors: Martina H Stenzel, Thomas P DavisAbstract:Polystyrene stars were synthesized with reversible addition–fragmentation chain-transfer (RAFT) polymerization. The core of the stars comprised a Trithiocarbonate heptafunctional β-cyclodextrin ring. Polymerizations were performed at 100 and 120 °C in the absence of an extraneous initiator and at 60 °C in the presence of a radical initiator. Monofunctional Trithiocarbonate was also synthesized and used to make linear polystyrene to allow direct a comparison with the star synthesis. In all cases, the polymerization kinetics conformed to pseudo-first-order behavior. The measured molecular weights of the stars were found to deviate from those predicted on the basis of the monomer/Trithiocarbonate group ratio. The extent of this deviation was dependent on the polymerization temperature, RAFT agent concentration, and conversion. Despite the low radical concentrations, termination reactions are suggested to play a significant role in the seven-arm polystyrene star syntheses. The synthetic method was found to be suitable for generating star block structures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4498–4512, 2002
Thomas P Davis - One of the best experts on this subject based on the ideXlab platform.
-
efficient usage of thiocarbonates for both the production and the biofunctionalization of polymers
Macromolecular Rapid Communications, 2009Co-Authors: Cyrille Boyer, Volga Bulmus, Thomas P DavisAbstract:End group modification of polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization was accomplished by conversion of Trithiocarbonate into reactive functions able to conjugate easily with biomolecules or bioactive functionality. Polymers were prepared by RAFT, and subsequent aminolysis led to sulfhydryl-terminated polymers that reacted in situ with an excess of dithiopyridyl disulfide to yield pyridyl disulfide-terminated macromolecules or in the presence of ene to yield functional polymers. In the first route, the pyridyl disulfide end groups allowed coupling with oligonucleotide and peptide. The second approach exploited thiol-ene chemistry to couple polymers and model compounds such as carbohydrate and biotin with high yield.
-
shell cross linked vesicles synthesized from block copolymers of poly d l lactide and poly n isopropyl acrylamide as thermoresponsive nanocontainers
Langmuir, 2004Co-Authors: Michelle Hales, Thomas P Davis, Christopher Barnerkowollik, Martina H StenzelAbstract:A polylactide (D,L-PLA) macroRAFT agent was prepared by utilizing a hydroxyl-functional Trithiocarbonate as a coinitiator for the ring-opening polymerization. The length of the resultant polymer was controlled by the concentration of the coinitiator leading to the formation of two PLA polymers with M(n) = 12500 g mol(-)(1) (PDI = 1.46) and M(n) = 20500 g mol(-)(1) (PDI = 1.38) each with omega-Trithiocarbonate functionality. Chain extension of PLA via the RAFT (free radical) polymerization of N-isopropyl acrylamide (NIPAAm) resulted in the formation of amphiphilic block copolymers with the PNIPAAm block increasing in size with conversion. TEM measurements of the aggregates obtained by self-organization of the block copolymers in aqueous solutions indicated the formation of vesicles. The sizes of these aggregates were influenced by the ratio of both blocks and the molecular weight of each block. The lower critical solution temperature (LCST) of the block copolymer was largely unaffected by the size of each block. UV turbidity measurements indicated a higher LCST for the block copolymers than for the corresponding PNIPAAm homopolymers. Stabilization of the vesicles was attained by a cross-linking chain extension of the PNIPAAm block using hexamethylene diacrylate. As the Trithiocarbonate group was located between the PLA and PNIPAAm blocks, the chain extension resulted in a cross-linked layer between the core and corona of the vesicles.
-
Shell-cross-linked vesicles synthesized from block copolymers of poly(D,L-lactide) and poly(N-isopropyl acrylamide) as thermoresponsive nanocontainers
Langmuir, 2004Co-Authors: Michelle Hales, Thomas P Davis, Christopher Barner-kowollik, Martina H StenzelAbstract:A polylactide (D,L-PLA) macroRAFT agent was prepared by utilizing a hydroxyl-functional Trithiocarbonate as a coinitiator for the ring-opening polymerization. The length of the resultant polymer was controlled by the concentration of the coinitiator leading to the formation of two PLA polymers with Mn = 12500 g mol-1 (PDI = 1.46) and Mn = 20500 g mol-1 (PDI = 1.38) each with ω-Trithiocarbonate functionality. Chain extension of PLA via the RAFT (free radical) polymerization of N-isopropyl acrylamide (NIPAAm) resulted in the formation of amphiphilic block copolymers with the PNIPAAm block increasing in size with conversion. TEM measurements of the aggregates obtained by self-organization of the block copolymers in aqueous solutions indicated the formation of vesicles. The sizes of these aggregates were influenced by the ratio of both blocks and the molecular weight of each block. The lower critical solution temperature (LCST) of the block copolymer was largely unaffected by the size of each block. UV turbidity measurements indicated a higher LCST for the block copolymers than for the corresponding PNIPAAm homopolymers. Stabilization of the vesicles was attained by a cross-linking chain extension of the PNIPAAm block using hexamethylene diacrylate. As the Trithiocarbonate group was located between the PLA and PNIPAAm blocks, the chain extension resulted in a cross-linked layer between the core and corona of the vesicles.
-
star polymer synthesis using Trithiocarbonate functional β cyclodextrin cores reversible addition fragmentation chain transfer polymerization
Journal of Polymer Science Part A, 2002Co-Authors: Martina H Stenzel, Thomas P DavisAbstract:Polystyrene stars were synthesized with reversible addition-fragmentation chain-transfer (RAFT) polymerization. The core of the stars comprised a Trithiocarbonate heptafunctional beta-cyclodextrin ring. Polymerizations were performed at 100 and 120 degreesC in the absence of an extraneous initiator and at 60 degreesC in the presence of a radical initiator. Monofunctional Trithiocarbonate was also synthesized and used to make linear polystyrene to allow direct a comparison with the star synthesis. In all cases, the polymerization kinetics conformed to pseudo-first-order behavior. The measured molecular weights of the stars were found to deviate from those predicted on the basis of the monomer/Trithiocarbonate group ratio. The extent of this deviation was dependent on the polymerization temperature, RAFT agent concentration, and conversion. Despite the low radical concentrations, termination reactions are suggested to play a significant role in the seven-arm polystyrene star syntheses. The synthetic method was found to be suitable for generating star block structures. (C) 2002 Wiley Periodicals, Inc.
-
star polymer synthesis using Trithiocarbonate functional β cyclodextrin cores reversible addition fragmentation chain transfer polymerization
Journal of Polymer Science Part A, 2002Co-Authors: Martina H Stenzel, Thomas P DavisAbstract:Polystyrene stars were synthesized with reversible addition–fragmentation chain-transfer (RAFT) polymerization. The core of the stars comprised a Trithiocarbonate heptafunctional β-cyclodextrin ring. Polymerizations were performed at 100 and 120 °C in the absence of an extraneous initiator and at 60 °C in the presence of a radical initiator. Monofunctional Trithiocarbonate was also synthesized and used to make linear polystyrene to allow direct a comparison with the star synthesis. In all cases, the polymerization kinetics conformed to pseudo-first-order behavior. The measured molecular weights of the stars were found to deviate from those predicted on the basis of the monomer/Trithiocarbonate group ratio. The extent of this deviation was dependent on the polymerization temperature, RAFT agent concentration, and conversion. Despite the low radical concentrations, termination reactions are suggested to play a significant role in the seven-arm polystyrene star syntheses. The synthetic method was found to be suitable for generating star block structures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4498–4512, 2002
Krzysztof Matyjaszewski - One of the best experts on this subject based on the ideXlab platform.
-
transformation of gels via catalyst free selective raft photoactivation
Polymer Chemistry, 2019Co-Authors: Sivaprakash Shanmugam, Cyrille Boyer, Julia Cuthbert, Jacob Flum, Marco Fantin, Tomasz Kowalewski, Krzysztof MatyjaszewskiAbstract:This work explores the concept of structurally tailored and engineered macromolecular (STEM) networks by proposing a novel metal-free approach to prepare the networks. STEM networks are composed of polymer networks with latent initiator sites affording post-synthesis modification. The proposed approach relies on selectively activating the fragmentation of Trithiocarbonate RAFT agent by relying on visible light RAFT iniferter photolysis coupled with RAFT addition–fragmentation process. The two-step synthesis explored in this work generates networks that are compositionally and mechanically differentiated than their pristine network. In addition, by careful selection of crosslinkers, conventional poly(ethylene glycol) dimethacrylate (Mn = 750) or Trithiocarbonate dimethacrylate crosslinker (bis[(2-propionate)ethyl methacrylate] Trithiocarbonate (bisPEMAT)), and varying concentrations of RAFT inimer (2-(2-(n-butylTrithiocarbonate)-propionate)ethyl methacrylate (BTPEMA)), three different types of primary (STEM-0) poly(methyl methacrylate) (PMMA) networks were generated under green light irradiation. These networks were then modified with methyl acrylate (MA) or N,N-dimethylacrylamide (DMA), under blue light irradiation to yield STEM-1 gels that are either stiffer or softer with different responses to polarity (hydrophilicity/hydrophobicity).
-
responsive gels based on a dynamic covalent Trithiocarbonate cross linker
Macromolecules, 2010Co-Authors: Renaud Nicolay, Jun Kamada, Abigail Van Wassen, Krzysztof MatyjaszewskiAbstract:Dimethacrylate Trithiocarbonate was synthesized and used as a dynamic covalent cross-linker to prepare PMMA and PSt gels via radical polymerization. The swelling properties of the PMMA gels were studied and showed that in the presence of radicals the gels reorganize to accommodate forces generated by the swelling processes. This reshuffling of the cross-link network yields an increase in the swelling ratio (up to 300% increase) of the PMMA gels. Two different radical generators, a thermal initiator and a CuI/L complex, were successfully used to trigger the reorganization of the gels. To illustrate the broad utility of the procedure, three discrete pieces of gels were fused into one single piece to demonstrate that dynamic covalent cross-linkers can be used to prepare materials that can be reprocessed and/or undergo self-repair.
-
dibromoTrithiocarbonate iniferter for concurrent atrp and raft polymerization effect of monomer catalyst and chain transfer agent structure on the polymerization mechanism
Macromolecules, 2008Co-Authors: Yungwan Kwak Renaud Nicolay, Krzysztof MatyjaszewskiAbstract:An iniferter comprising a Trithiocarbonate (TTC) moiety and two bromine chain ends was prepared and used to successfully conduct, independently or concurrently, atom transfer radical polymerization...
Mahdi Abdollahi - One of the best experts on this subject based on the ideXlab platform.
-
Kinetic investigation of the reversible addition-fragmentation chain transfer polymerization of 1,3-butadiene
Journal of Polymer Research, 2013Co-Authors: Pejman Ganjeh-anzabi, Vahid Haddadi-asl, Mehdi Salami-kalajahi, Mahdi AbdollahiAbstract:Reversible addition-fragmentation chain transfer (RAFT) polymerization of 1,3-butadiene using a Trithiocarbonate chain transfer agent, S -1-dodecyl- S′ -( r , r′ -dimethyl- r″ -acetic acid)Trithiocarbonate (DDMAT), was investigated. For the first time, comprehensive kinetic study of solution RAFT polymerization of 1,3-butadiene is reported. Effect of some factors such as RAFT agent and initiator concentration and initial molar ratio of monomer to both RAFT agent and initiator on the rate of polymerization and molecular weight distribution (MWD) were examined experimentally and discussed quantitatively. The validity of quasi-steady state approximation (QSSA) was shown and the rate of polymerization’s equation was obtained. Good compatibility with the experimental and theoretical values of molecular weights was obtained. Also, polybutadiene samples with narrow molecular weight distribution were synthesized.
