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Narrow Polydispersities (narrow + polydispersity)
Selected AbstractsTitanium and zirconium complexes containing modified TREN ligands for the polymerization of 1-alkenes,A comparative studyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007Padmanabhan Sudhakar Abstract The titanium and zirconium complexes in C3 and Cs symmetric forms synthesized from corresponding aminotriols in combination with MAO polymerized 1-hexene in a controlled manner. When the polymerization temperature was lowered, they gave high molecular weight monodisperse polyhexene with narrow polydispersities indicating quazi-living systems. The isotactic polyhexene obtained from C3 titanium catalyst has the molecular weight of around 46,500 with PDI of 1.3 and the hemi-isotactic polymer from Cs titanium catalyst has the molecular weight of around 617,000 with PDI of 1.3. The analogues zirconium complexes upon activation with MAO polymerize hexene to give polyhexene having molecular weight of 53,000 (C3) and 626,000 (pseudo-Cs) with PDI ranging from 1.2 to 1.4. The MIX-titanium catalyst prepared from the 50:50 mixture of aminotriols was also able to polymerize 1-hexene and the GPC traces of the polyhexene suggests that even though the catalyst was formed from the mixture of aminotriols, the C3 and Cs symmetry of the catalysts retain its originality avoiding the formation of aggregates or polymeric forms. When one of the arms of aminotriol was methylated yield C2 and meso aminodiol ligands and their corresponding titanium and zirconium complexes gave higher molecular weight polyhexenes with lower PDI (C2 -Zr- Mn: 260,000; PDI: 1.05,1.10; mesoZr- Mn: 220,000; PDI: 1.05,1.10) possibly suggesting that these systems are close to living systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5470,5479, 2007 [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] Ambient-temperature copper-catalyzed atom transfer radical polymerization of methacrylates in ethylene glycol solventsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2005Solomon M. Kimani Abstract The use of ethylene glycol solvents in the room-temperature atom transfer radical polymerization (ATRP) of various hydrophobic and hydrophilic methacrylates is demonstrated. Unlike many of the very polar solvents described in the literature for room-temperature ATRP, these solvents have good solvency for a wide range of polymers and monomers and are cheap and relatively nontoxic. Ethylene glycols with one hydroxyl and one methoxy group, such as tri(ethylene glycol) monomethyl ether (TEGMME), provide optimal results. The polymerization of methyl methacrylate in TEGMME with CuBr/N,N,N,N,,N,-pentamethyldiethylenetriamine as the catalyst requires the addition of CuCl2 at the beginning of the reaction to produce well-controlled polymerizations. This leads to polymers with predictable molecular weights and relatively narrow polydispersities. Polymerization in solvents that are fully methoxy-capped terminate prematurely because of catalyst precipitation. The electrochemical behavior of copper complexes in selected solvents is examined to determine why these solvents provide good rates at room temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1588,1598, 2005 [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] Living free-radical polymerization (reversible addition,fragmentation chain transfer) of 6-[4-(4,-methoxyphenyl)phenoxy]hexyl methacrylate: A route to architectural control of side-chain liquid-crystalline polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2003Xiaojuan Hao Abstract Side-chain liquid-crystalline polymers of 6-[4-(4,-methoxyphenyl)phenoxy]hexyl methacrylate with controlled molecular weights and narrow polydispersities were prepared via reversible addition,fragmentation chain transfer (RAFT) polymerization with 2-(2-cyanopropyl) dithiobenzoate as the RAFT agent. Differential scanning calorimetry studies showed that the polymers produced via the RAFT process had a narrower thermal stability range of the liquid-crystalline mesophase than the polymers formed via conventional free-radical polymerization. In addition, a chain length dependence of this stability range was found. The generated RAFT polymers displayed optical textures similar to those of polymers produced via conventional free-radical polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2949,2963, 2003 [source] Synthesis of a novel hybrid liquid-crystalline rod,coil diblock copolymerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2003Yi Yi Abstract A series of novel rod,coil diblock copolymers on the basis of mesogen-jacketed liquid-crystalline polymer were successfully prepared by atom transfer radical polymerization from the flexible polydimethylsiloxane (PDMS) macroinitiator. The hybrid diblock copolymers, poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene}- block -polydimethylsiloxane, had number-average molecular weights (Mn's) ranging from 9500 to 30,900 and relatively narrow polydispersities (,1.34). The polymerization proceeded with first-order kinetics. Data from differential scanning calorimetry validated the microphase separation of the diblock copolymers. All block copolymers exhibited thermotropic liquid-crystalline behavior except for the one with Mn being 9500. Four liquid-crystalline diblock copolymers with PDMS weight fractions of more than 18% had two distinctive glass-transition temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1799,1806, 2003 [source] Stannous(II) trifluoromethane sulfonate: a versatile catalyst for the controlled ring-opening polymerization of lactides: Formation of stereoregular surfaces from polylactide "brushes"JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2001Michael Möller Abstract A general method for the controlled synthesis of polylactide in solution and from solid supports is presented. The evaluation of stannous(II) trifluoromethane sulfonate [Sn(OTf)2] and scandium(III) trifluoromethane sulfonate [Sc(OTf)3] as catalysts for the ring-opening polymerization (ROP) of L -, D -, and L,D -lactide is described as a route to polylactide using mild and highly selective conditions. These triflate catalysts must be used in conjunction with a nucleophilic compound such as an alcohol that is the actual initiating species via the active metal alkoxide species. Consistent with this process, 1H NMR analysis revealed that the ,-chain-end bears the ester from the initiating alcohol, and upon hydrolysis of the active metal alkoxide chain end, a ,-hydroxyl chain end was clearly detected. Polymers of predictable molecular weights and narrow polydispersities were obtained in high yields in accordance with a controlled polymerization process. The addition of base either as a solvent or additive significantly enhanced the polymerization rate with minimal loss to the polymerization control. The ROP of lactide isomers from an initiator, HO(CH2CH2O)3(CH2)11SH, self-assembled onto a gold surface using Sn(OTf)2 produced polylactide brushes under living conditions and provides the opportunity to prepare stereoregular or chiral surfaces by polymerization of enantiomerically pure monomers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3529,3538, 2001 [source] Synthesis of Comb Tri- and Tetrablock Copolymers Catalyzed by the Grubbs First Generation CatalystMACROMOLECULAR RAPID COMMUNICATIONS, Issue 16 2009M. Brett Runge Abstract High molecular weight tri- and tetrablock copolymers were synthesized from the commercially available Grubbs first generation catalyst for the first time. These polymers had degrees of polymerization from 430 to 1,100, molecular weights up to 419,000 g,·,mol,1, and narrow polydispersities. Oxanorbornene monomers were chosen due to their fast rates of polymerization and slow rates of cross metathesis. Polystyrene arms were grown from selected blocks by atom transfer radical polymerization to yield architecturally complex comb tri- and tetrablock copolymers. These polymers self-assembled in the solid state into ordered morphologies that were characterized by scanning electron microscopy. [source] Synthesis of Well-Defined Figure-of-Eight-Shaped Polymers by a Combination of ATRP and Click ChemistryMACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2008Gang-Yin Shi Abstract Well-defined figure-of-eight-shaped (8-shaped) polystyrene (PS) with controlled molecular weight and narrow polydispersities has been prepared by the combination of atom transfer radical polymerization (ATRP) and click chemistry. The synthesis involves two steps: 1) Preparation of a linear tetrafunctional PS with two azido groups, one at each end of the polymer chain, and two acetylene groups at the middle of the chain. 2) Intramolecular cyclization of the linear tetrafunctional PS at a very low concentration by a click reaction to produce the 8-shaped polystyrenes. The resulting intermediates and the target polymers were characterized by 1H NMR and FT-IR spectroscopy, and gel permeation chromatography. The glass transition temperatures (Tgs) were determined by differential scanning calorimetry and it was found that the decrease in chain mobility by cyclization resulted in higher Tgs for 8-shaped polystyrenes as compared to their corresponding precursors. [source] Synthesis of Amphiphilic ABC Triblock Copolymers with PEO as the Middle BlockMACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2004Surbhi Mahajan Abstract Summary: Stepwise anionic polymerization, catalytic hydrogenation, and atom transfer radical polymerization were performed to synthesize an amphiphilic ABC triblock copolymer, poly(ethylene- alt -propylene)- block -poly(ethylene oxide)- block -poly(hexyl methacrylate) (PEP- b -PEO- b -PHMA), with hydrophilic PEO as the middle block. The resulting block copolymers have well-defined molecular weights and narrow molecular weight distributions as revealed by 1H NMR spectroscopy and gel permeation chromatography. GPC chromatograms of an ABC triblock copolymer, PEP- b -PEO- b -PHMA, and its intermediate precursors exhibiting narrow polydispersities. [source] Fluorocarbon End-functionalized Polymers from Poly(arylether) Dendritic InitiatorsMACROMOLECULAR SYMPOSIA, Issue 1 2005A. Pillay Narrainen Abstract Fréchet-type poly(arylether) first and second generation (G1 and G2 respectively) dendrons were prepared from 1-(bromomethyl)-3,5-bis(trifluoromethyl)benzene. The latter and the brominated versions of the two dendrons were successfully employed in the copper mediated living radical polymerization (LRP) of styrene-d8 giving polymers of predictable molecular weights and narrow polydispersities. Contact angle measurements and ion beam analysis were used to explore the adsorption of these materials to the air-polymer surface in blended films with unfunctionalized hydrogenous polystyrene. Although contact angle analysis indicated only modest changes in the hydrophobicity and lipophobicity of the surface, ion beam analysis clearly showed the formation of an excess layer of dendron functionalized polymer at the exposed surface that increased with increasing fluorine content. [source] Synthesis of block copolymers by combination of ATRP and photoiniferter processesPOLYMER INTERNATIONAL, Issue 10 2008Yasemin Yuksel Durmaz Abstract BACKGROUND: Block copolymers of monomers polymerizing by different mechanisms can be prepared by the transformation approach. A wide range of combinations of different polymerization modes has been reported in the literature. In this work, the transformation approach was further extended to the preparation of block copolymers by combining atom transfer radical polymerization (ATRP) and photoiniferter processes. RESULTS: Photoactive morpholine-4-dithiocarbamate-terminated polystyrene (MDC-PS-MDC) was prepared by the reaction of dibrominated polystyrene, obtained by ATRP, with morpholine-4-dithiocarbamate sodium salt in dimethylformamide. The structure of MDC-PS-MDC was confirmed by 1H NMR and UV-visible spectral analysis. The ability of MDC-PS-MDC to act as a photoiniferter for the block copolymerization of methyl acrylate was examined. The polymerization shows a ,living' character at up to 25% conversion and produces well-defined polymers with molecular weights close to those predicted from theory and relatively narrow polydispersities (Mw/Mn , 1.40). CONCLUSION: It is demonstrated that the end groups of polymers obtained by ATRP can be converted into morpholino-4-dithiocarbamate groups which act as photoiniferters. In this way, the desired mechanistic transformation between two controlled free radical polymerization methods can be achieved. Copyright © 2008 Society of Chemical Industry [source] Copolymerization of Cyclohexene Oxide with CO2 by Using Intramolecular Dinuclear Zinc CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2005Youli Xiao Abstract The intramolecular dinuclear zinc complexes generated in situ from the reaction of multidentate semi-azacrown ether ligands with Et2Zn, followed by treatment with an alcohol additive, were found to promote the copolymerization of CO2 and cyclohexene oxide (CHO) with completely alternating polycarbonate selectivity and high efficiency. With this type of novel initiator, the copolymerization could be accomplished under mild conditions at 1 atm pressure of CO2, which represents a significant advantage over most catalytic systems developed for this reaction so far. The copolymerization reaction was demonstrated to be a living process as a result of the narrow polydispersities and the linear increase in the molecular weight with conversion of CHO. In addition, the solid-state structure of the dinuclear zinc complex was characterized by X-ray crystal structural analysis and can be considered as a model of the active catalyst. On the basis of the various efforts made to understand the mechanisms of the catalytic reaction, including MALDI-TOF mass analysis of the copolymers' end-groups, the effect of alcohol additives on the catalysis and CO2 pressure on the conversion of CHO, as well as the kinetic data gained from in situ IR spectroscopy, a plausible catalytic cycle for the present reaction system is outlined. The copolymerization is initiated by the insertion of CO2 into the ZnOEt bond to afford a carbonate,ester-bridged complex. The dinuclear zinc structure of the catalyst remains intact throughout the copolymerization. The bridged zinc centers may have a synergistic effect on the copolymerization reaction; one zinc center could activate the epoxide through its coordination and the second zinc atom may be responsible for carbonate propagation by nucleophilic attack by the carbonate ester on the back side of the cis -epoxide ring to afford the carbonate. The mechanistic implication of this is particularly important for future research into the design of efficient and practical catalysts for the copolymerization of epoxides with CO2. [source] Preparation of polyacrylonitrile with improved isotacticity and low polydispersityJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Jianguo Jiang Abstract The preparation of a polymer with both low polydispersity and high tacticity is one current challenge we face and warrants thorough investigation from both the theoretical and experimental standpoints. In this study, we synthesized polyacrylonitrile (PAN) with simultaneously controlled molecular weight and tacticity on the basis of the strategy of the atom transfer radical polymerization (ATRP) of acrylonitrile (AN) in the presence of Lewis acids. A new combined initiation system of 3-bromopropionitrile (3-BPN)/Cu2O/N,N,N,,N,-tetramethylethylenediamine (TMEDA) was used for the ATRP of AN for the first time. When the polymerization was performed with the ratio [AN]0/[Initiator]0/[Cu2O]0/[TMEDA]0 = 190/1/0.5/1.5 (where the subscript 0 indicates the initial conditions) in ethylene carbonate at 60°C for 48 h, the polydispersity of the obtained PAN was 1.13, and the molecular weight was up to 13,710. The polymerization kinetics results show that the polymerizations proceeded with a living/controlled nature except that an induction period existed during the polymerization process because of the lower initiating activity of 3-BPN. Also, two kinds of Lewis acid, AlCl3 and yttrium trifluororomethanesulflnate, were used in the ATRP system of AN for the tacticity control. The addition of 0.01 equiv (relative to AN) of the Lewis acid AlCl3 in the polymerization afforded PAN with an improved isotacticity [meso/meso triad (mm) = 0.32] and a very narrow polydispersity (1.06). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Functional syndiotactic poly(,-hydroxyalkanoate)s via stereoselective ring-opening copolymerization of rac -,-butyrolactone and rac -allyl-,-butyrolactoneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2009Noureddine Ajellal Abstract The copolymerization of racemic ,-butyrolactone (rac -BLMe) with racemic "allyl-,-butyrolactone" (rac -BLallyl) in toluene, catalyzed by the discrete amino-alkoxy-bis(phenolate) yttrium-amido complex 1, gave new poly(,-hydroxyalkanoate)s with unsaturated side chains. The poly(BLMe - co -BLallyl) copolymers produced have a highly syndiotactic backbone structure (Pr = 0.80,0.84) with a random enchainment of monomer units, as evidenced by 13C NMR, and high molecular weight (Mn up to 58,000 g mol,1) with a narrow polydispersity (Mw/Mn = 1.07,1.37), as determined by GPC. The comonomer incorporation (5,50 mol % rac -BLallyl) was a linear function of the feed ratio. The pendant vinyl bond of the side-chains in those poly(BLMe - co -BLallyl) copolymers allowed the effective introduction of hydroxy or epoxy groups via dihydroxylation, hydroboration-oxidation or epoxidation reactions. NMR studies indicated that all of these transformations proceed in an essentially quantitative conversion and do not affect the macromolecular architecture. Some thermal properties (Tm, ,Hm, Tg) of the prepared polymers have been also evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3177,3189, 2009 [source] Ferrocenyl-functionalized long chain branched polydienesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2009Frederik Wurm Abstract A convenient two-step approach for the synthesis of ferrocenyl-functionalized long chain branched polydienes, based on both butadiene and isoprene, respectively, is presented. Classical living anionic polymerization was used to synthesize different ABn type poly(diene) macromonomers with moderate molecular weights between 1700 and 3200 g/mol and narrow polydispersity. Quantitative end-capping with chlorodimethylsilane resulted in the desired ABn macromonomer structures. In the ensuing Pt-catalyzed hydrosilylation polyaddition, branched, functionalized polydienes were obtained by a concurrent ABn + AR type of copolymerization with mono- and difunctional ferrocenyl silanes (fcSiMe2H or fc2SiMeH). Molecular weights of the branched polymers were in the range of 10,000 to 44,000 g/mol (SEC/MALLS). Because of the large number of functional end groups, high loading with ferrocene units up to 63 wt % of ferrocene was achieved. Detailed studies showed full conversion of the functional silanes and incorporation into the branched polymer. Further studies using DSC, TGA, and cyclovoltammetry (CV) measurements have been performed. Electrochemical studies demonstrated different electrochemical properties for fcSiMe2 - and fc2SiMe-units. The CVs of polymers modified with diferrocenylsilane units exhibit the pattern of communicating ferrocenyl sites with two distinct, separate oxidation waves. The polymers were also deposited on an electrode surface and the electrodes investigated via CV, showing formation of electroactive films with promising results for the use of the materials in biosensors. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2518,2529, 2009 [source] A novel rate-accelerating additive for atom transfer radical polymerization of styreneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2007Zhuang Jiaming Abstract The polymerization of styrene was mediated by copper (I) bromide/pentramethldiethyltriamine (PMDETA) using ethyl 2-bromopropionate (EBP) as initiator and a catalytic amount of malononitrile (MN) as a novel rate-accelerating additive. The optimal molar ratios of MN/EBP under which the polymerization of styrene can proceed fastest was 4:1. The rate-enhancement-efficiency had a dependence on temperature and the apparent rate constant of polymerization improved by a factor of 2.67 at 85 °C. Polymerization resulted in a conversion as high as 87% in 4.3 h in the presence of MN, while a conversion of 79.7% was gained even in 10 h without MN at 85 °C. The polymerizations of styrene in the presence of MN proceeded in a living fashion indicated by the first-order kinetic plots, with the increase of Mn with respect to conversion and the relatively narrow polydispersity. The possible rate enhancing mechanism is that the addition of MN weakens the coordination between the copper center and ligand and facilitates the atom transfer process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4082,4090, 2007 [source] Atom transfer radical homo- and block copolymerization of methyl 1-bicyclobutanecarboxylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2002Xiao-Ping Chen Abstract A non-olefinic monomer, methyl 1-bicyclobutanecarboxylate (MBC), was successfully polymerized by the controlled/"living" atom transfer radical polymerization (ATRP) technique, resulting in a well-defined homopolymer, PMBC, with only cyclobutane ring units in the polymer chain. An AB block copolymer poly(methyl 1-bicyclobutanecarboxylate)- b -polystyrene (PMBC- b -PS), having an all-ring unit segment, was also synthesized with narrow polydispersity and designed number-average molecular weight in addition to precise end groups. The 1H NMR spectra, glass-transition temperature, and thermal stability of PMBC, PMBC- b -PS, and PS- b -PMBC were investigated. The experimental results showed that the cyclobutane rings in the two block polymers improved their thermal stability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1929,1936, 2002 [source] Novel Amphiphilic Styrene-Based Block Copolymers for Induced Surface ReconstructionMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2008Lutz Funk Abstract This paper describes the synthesis of amphiphilic block copolymers by living radical polymerization (NMP) of new styrene-like monomers. The polar monomers (ethylene oxide side chains and free hydroxyl- or amino-groups after deprotection) were polymerized in a "protected form" to adjust the solubility of the monomers. In this way high molar mass polymers with a narrow polydispersity (around or below 1.2) were accessible. In the bulk state hydrophobic and hydrophilic domains demix. By exposing thin films of these polymers to vacuum (air) or alternatively to water or a hydrophilic surface it becomes possible to switch the surface polarity reversibly between contact angles of about 105° and 83° as a result of surface reconstruction. Through side chains of different length and with different functionalities, it was possible to adjust the glass transition temperatures to values between ,2,°C to 140,°C for the hydrophilic blocks and ,30,°C to 100,°C for the hydrophobic block. The wide range of the glass temperatures allowed it to find a block copolymer system with a slow kinetic concerning the surface reconstruction process, so that a mechanistic examination of the process by AFM was possible. It got, thereby, possible to detect the break-up of the hydrophobic surface lamella and the upfold of the hydrophilic lamella in contact with water. [source] A Novel Strategy to Synthesize Double Comb-Shaped Water Soluble Copolymer by RAFT PolymerizationMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2006De-Hui Han Abstract Summary: A double comb-shaped water soluble copolymer, poly[poly(ethylene oxide) methyl ether methacrylate]- block -poly(N -isopropylacrylamide)- block -poly[poly (ethylene oxide) methyl ether methacrylate], abbreviated as [P(MA-MPEO)- block -PNIPAM- block -P(MA-MPEO)], with a controlled molecular weight and narrow polydispersity was successively synthesized using a macromonomer technique. The 60Co , irradiation polymerization of MA-MPEO in the presence of dibenzyl trithiocarbonate (DBTTC) at room temperature afforded a polymer, P(MA-MPEO)-SC(S)S-P(MA-MPEO), which was subsequently used as a macro RAFT agent in the RAFT polymerization of N -isopropylacrylamide, and water soluble double comb-shaped copolymers, P(MA-MPEO)- block -PNIPAM- block -P(MA-MPEO), were successfully obtained. Structure of the double comb-shaped copolymer. [source] Cloud-Point Pressure Curves of Ethene/Poly[ethylene- co -((meth)acrylic acid)] MixturesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2003Michael Buback Abstract Ethene-methacrylic acid (MAA) and ethene-acrylic acid (AA) copolymers of narrow polydispersity and high chemical homogeneity have been synthesized at acid unit copolymer contents up to 9 mol-% within a continuously operated stirred tank reactor at overall monomer conversions of about 2%. Cloud-point pressures (CPPs) of mixtures of 3 wt.-% copolymer in ethene (E) have been measured in an optical high-pressure cell at pressures and temperatures up to 3,000 bar and 260,°C, respectively. The CPP weakly increases with acid copolymer content up to about 3.5 mol-%. Toward higher acid contents, the CPP is strongly enhanced, in particular at the lower edge of the experimental temperature range at around 200,°C. This increase in CPP is more pronounced for the AA than for the MAA systems. The data suggest that hydrogen-bonding interactions are operative in the pressurized E/poly(E- co -(M)AA) mixtures at temperatures of 260,°C and perhaps even above. E-AA and E-MAA copolymers with acid contents of about 5.6 mol-% have also been completely methyl-esterified to yield the associated methyl esters. The CPPs of the resulting E-methyl acrylate and E-methyl methacrylate copolymers in mixtures with E are significantly below the CPPs of the corresponding E/poly(E- co -(M)AA) systems. Cloud-point pressure vs temperature curves for several E/poly(E- co -methacrylic acid) systems. The subscripts denote copolymer content in mol-%. A cloud-point pressure curve for E/polyethylene (PE) is included for comparison. [source] Defined Poly[styrene- block -(ferrocenylmethyl methacrylate)] Diblock Copolymers via Living Anionic PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2009Markus Gallei Abstract Ferrocenylmethyl methacrylate (FMMA) is one of the very few metallocene-based monomers that are promising candidates for truly living anionic polymerization. Nevertheless, FMMA homopolymers with a narrow polydispersity, or block copolymerization studies that result in satisfying blocking efficiencies, are unknown so far. Here we describe a procedure that leads to highly regular FMMA-based polymers for the first time, characterized by polydispersity indices (PDI) of less that 1.05 and very high blocking efficiencies (>95%) in sequential copolymerization with styrene. Some of the obtained poly[styrene- block -(ferrocenylmethyl methacrylate)]s show unusual microphase morphologies, presumably the consequence of high Tgs causing ,frustrated' non-equilibrium states. [source] Synthesis and Cyclohexene Oxide/Carbon Dioxide Copolymerizations of Zinc Acetate Complexes Bearing Bidentate Pyridine-Alkoxide LigandsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2004Il Kim Abstract Summary: The reaction of 2-lithio-6-methylpyridine or 2-lithiopyridine and the appropriate diaryl ketone followed by hydrolysis yields 6-Me-pyCAr2OH pyridine alcohols or pyCAr2OH pyridine alcohols. The reactions of zinc acetate with 1 equiv. of the lithiated products of the ligands proceed rapidly to afford LiOAc salt and mono-ligand complexes (6-Me-pyCAr2O)Zn(OAc) and (pyCAr2O)Zn(OAc), respectively, in high yield. The copolymerizations of carbon dioxide with cyclohexene oxide were investigated. The (6-Me-pyCAr2O)Zn(OAc) showed moderate yield and CO2 incorporation. The [6-Me-pyC(4-Cl-C6H4)2O]Zn(OAc) complex gave large polymers with high proportions of carbonate linkage (>60%) and narrow polydispersity, indicating single active sites. The monoligated Zn complexes synthesized and used here as catalysts for the copolymerization of cyclohexene oxide and carbon dioxide. [source] Electroactive Linear,Hyperbranched Block Copolymers Based on Linear Poly(ferrocenylsilane)s and Hyperbranched Poly(carbosilane)sCHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2009Frederik Wurm Dipl.-Chem. Abstract A convenient two-step protocol is presented for synthesis of linear-hyperbranched diblock copolymers consisting of a linear, organometallic poly(ferrocenylsilane) (PFS) block and hyperbranched poly(carbosilane) (hbPCS) segments. Linear PFS diblock copolymers were synthesized through photolytic ring-opening polymerization of dimethyl[1]silaferrocenophane as the first block and methylvinyl[1]silaferrocenophane as the second. These block copolymers served as polyfunctional cores in a subsequent hydrosilylation polyaddition of different silane-based AB2 monomers. Three AB2 monomers (methyldiallylsilane; methyldiundecenylsilane, and ferrocenyldiallylsilane) were investigated; they introduced structural diversity to the hyperbranched block and showed variable reactivity for the hydrosilylation reaction. In the case with the additional ferrocene moiety in the ferrocenyldiallylsilane monomer, an electroactive hyperbranched block was generated. No slow monomer addition was necessary for molecular-weight control of the hyperbranching polyaddition, as the core had much higher functionality and reactivity than the carbosilane monomers. Different block ratios were targeted and hybrid block copolymers with narrow polydispersity (<1.2) were obtained. All the resulting polymers were investigated and characterized by size exclusion chromatography, NMR spectroscopy, cyclic voltammetry, and TEM, and exhibited strongly anisotropic aggregation. [source] | ||||||||||