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Monomer Units (monomer + unit)
Selected AbstractsA Defect-Free Ring Polymer: Size-Controlled Cyclic Poly(tetrahydrofuran) Consisting Exclusively of the Monomer Unit,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2008Yasuyuki Tezuka Abstract A series of size-controlled, cyclic poly(tetrahydrofuran)s ( of 4,400,8,600) that consist exclusively of the monomer, i.e., oxytetramethylene, unit (I) have been prepared in high yield through the metathesis polymer cyclization of a telechelic precursor having allyl groups, 1, in the presence of a Grubbs catalyst, and the subsequent hydrogenation of the linking, i.e., 2-butenoxy, unit in the presence of an Adams' catalyst (PtO2). A remarkable topology effect has subsequently been observed upon the isothermal crystallization of these two model polymers, showing distinctive spherulite growth rates and spherulite morphologies in comparison with the relevant linear poly(tetrahydrofuran) counterpart that has ethoxy end groups (II). [source] Amplified Spontaneous Emission of Poly(ladder-type phenylene)s , The Influence of Photophysical Properties on ASE Thresholds,ADVANCED FUNCTIONAL MATERIALS, Issue 20 2008Frédéric Laquai Abstract Amplified spontaneous emission (ASE) of a series of blue-emitting poly(ladder-type phenylene)s (LPPP)s has been studied in thin film polymer waveguide structures. The chemically well-defined step-ladder polymers consist of an increasing number of bridged phenylene rings per monomer unit starting from fully arylated poly(ladder-type indenofluorene) up to poly(ladder-type pentaphenylene). The ASE characteristics of the polymers including the onset threshold values for ASE, the gain and loss coefficients as well as the photoluminescence (PL) properties, i.e., the solid state fluorescence lifetimes, decay kinetics and solid state quantum efficiencies have been studied by time-resolved PL spectroscopy. A fully arylated polyfluorene has been synthesized and its photophysical properties were compared to the step-ladder polymers. Steady-state photoinduced absorption and ultrafast transient absorption spectroscopy have been used to study excited state absorption of singlet and triplet states and polarons present in the solid state. The results demonstrate a minimum regarding the onset threshold value of ASE for a fully arylated poly(ladder-type indenofluorene) and a successive increase of the ASE threshold for the step-ladder polymers with more bridged phenylene rings. In particular, carbazole-containing step-ladder LPPPs exhibit significantly increased ASE threshold values as compared to their carbazole-free analogues due to a pronounced overlap of stimulated emission (SE) and photoinduced absorption (PA). [source] Donor,Acceptor C60 -Containing Polyferrocenylsilanes: Synthesis, Characterization, and Applications in Photodiode Devices,ADVANCED FUNCTIONAL MATERIALS, Issue 3 2008Masato Nanjo Abstract A series of polyferrocenylsilane (PFS) random copolymers containing covalently bound pendant [C60]fullerene groups, the first well-characterized metallopolymers with pendant C60 units, have been prepared and characterized. The fullerene content of the prepared copolymers ranges from 7 to 24% relative to monomer unit. The desired copolymers were synthesized in three steps: metal-catalyzed ring opening polymerization of sila[1]ferrocenophanes was performed to synthesize random copolymers of poly(ferrocenylmethylphenylsilane -co- ferrocenylchloromethylsilane); the resulting random PFSs were then functionalized by reaction with 11-azido-1-undecanol to give PFSs with pendant azide groups; the desired donor,acceptor C60 -containing PFSs were then synthesized by the reaction of the azide group in the side chains with C60 in toluene at 110,°C. The resulting C60 -containing PFSs are air-stable and soluble in aromatic solvents, chloroform, or THF. The UV-vis spectra of these materials show broad absorption up to 800 nm. Thin films of these materials were examined as the active layer in rare examples of all solid-state sandwich-type diode devices based on ferrocene-fullerene dyads. The devices exhibit photoconducting and photovoltaic responses, with an open circuit potential of ca. 0.3 V under white light illumination. [source] Polymer hydration and microphase decomposition in poly(N -vinylcaprolactam),water complexJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2003Vassili Lebedev Poly(N -vinylcaprolactam) (PVCL) is a synthetic analogue of biomolecules (enzymes, proteins). It demonstrates a specific hydration and undergoes a coil,globule transition. The PVCL,D2O system (PVCL mass M = 106) has been investigated by small-angle neutron scattering (SANS) at T = 296,316,K to identify the structural features of the collapse at concentration C = 0.5,wt% near the threshold of the coil overlap. (The collapse leads to the segregation of the phase enriched with polymer at T > 305,K). The SANS experiments at q = 0.1,5,nm,1 (scales from monomer unit to globule gyration radius RG, 16,nm) have revealed a stretched coil,globule transformation in the range 305,309,K. Using high-resolution SANS (q = 0.002,0.02 nm,1) the globule association to form fractal structures (sponge-like) of surface dimension DF, 2.4,2.6 was examined. The coexistence of globules and disordered chains (regions ,5,10,nm) was found. The growth of the content of globular phase was induced by the conformational transition in disordered molecular fragments from coiled (dimension D, 1.8) to stretched chains (D, 1.2). [source] Effect of conjugated core building block dibenzo[a,c]phenazine unit on ,-conjugated electrochromic polymers: Red-shifted absorptionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2010Elif Kose Unver Abstract A comparative investigation was undertaken for the electrosynthesis and electrochemical properties of three different electroactive polymers having a conjugated core building block, dibenzo[a,c]phenazine. A series of monomers has been synthesized as regards to thiophene based units; thiophene, 3-hexyl thiophene, and 3,4-ethylenedioxythiophene. The effects of different donor substituents on the polymers' electrochemical properties were examined by cyclic voltammetry. Introducing highly electron-donating (ethylene dioxy) group to the monomer enables solubility while also lowering the oxidation potential. The planarity of the monomer unit enhances ,-stacking and consequently lowering the Eg from 2.4 eV (PHTP) to 1.7 (PTBP). Cyclic voltammetry and spectroelectrochemical measurements revealed that 2,7-bis(4-hexylthiophen-2-yl)dibenzo[a,c]phenazine (HTP) and 2,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)dibenzo[a,c]phenazine (TBP) possessed electrochromic behavior. The colorimetry analysis revealed that while PTBP have a color change from red to blue, PHTP has yellow color at neutral state and blue color at oxidized state. Hence the presence of the phenazine derivative as the acceptor unit causes a red shift in the polymers' absorption to have a blue color. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1714,1720, 2010 [source] Direct measurements of the addition and recombination of acrylate radicals: Access to propagation and termination rate constants?JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2006J. Lalevée Abstract Acrylate radicals produced by the addition of an aminoalkyl radical to five acrylate monomers were directly observed by transient absorption spectroscopy, which allowed us to easily follow their chemical reactivity. It was possible (1) to characterize their absorption in the visible part of the spectrum, (2) to calculate their absorption properties, (3) to determine the energy barriers of the addition through quantum mechanical calculations, (4) to monitor the kinetics of the subsequent addition to another monomer unit, and (5) to follow the recombination of two acrylate radicals. These two latter points could mimic the propagation and termination reactions of polymerization-propagating acrylate radicals. Methacrylate and acrylonitrile radicals were also studied. The obtained results were in good agreement with the propagation rate constants determined by the well-established pulsed laser polymerization techniques. Our method could likely provide rapid access to both the propagation and termination rate constants in suitable systems and appears to be powerful and promising for studying and comparing the reactivities of different acrylate monomer structures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3577,3587, 2006 [source] Synthesis and SFM Study of Comb-Like Poly(4-vinylpyridinium) Salts and Their Complexes with SurfactantsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 13 2006Marat O. Gallyamov Abstract Summary: Poly(4-vinylpyridinium) bromides containing octyl and dodecyl pendant groups were synthesized. Bromide anions in these polymer salts were substituted with dodecylsulfate and bis(2-ethylhexylsuccinate) anions using ion-exchange reactions. Initially, P4VP and its derivatives loaded with hydrophobic groups were deposited on a mica surface from diluted solutions in chloroform for visualization. Images of single adsorbed macromolecules were obtained using scanning force microscopy. Original P4VP chains form partially compacted self-intersecting coils. Loading the polymer chains with large hydrophobic groups and especially the increase in the number of alkyl tails (see Figure) per monomer unit of the polymer chain leads to the stretching of the coils, and the comb-like macromolecules adopt more and more extended self-avoiding 2D conformations when deposited on the substrate. Polymer chains with large hydrophobic groups and increasing number of alkyl tails per monomer unit of the polymer chain. [source] Temperature and Pressure Effects on Local Structure and Chain Packing in cis -1,4-Polybutadiene from Detailed Molecular Dynamics SimulationsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006Georgia Tsolou Abstract Summary: We present results for the temperature and pressure dependence of local structure and chain packing in cis -1,4-polybutadiene (cis -1,4-PB) from detailed molecular dynamics (MD) simulations with a united-atom model. The simulations have been executed in the NPT statistical ensemble with a parallel, multiple time step MD algorithm, which allowed us to access simulation times up to 1 µs. Because of this, a 32 chain C128cis -1,4-PB system was successfully simulated over a wide range of temperature (from 430 to 195 K) and pressure (from 1 atm to 3 kbar) conditions. Simulation predictions are reported for the temperature and pressure dependence of the: (a) density; (b) chain characteristic ratio, Cn; (c) intermolecular pair distribution function, g(r), static structure factor, S(q), and first peak position, Qmax, in the S(q) pattern; (d) free volume around each monomer unit along a chain for the simulated polymer system. These were thoroughly compared against available experimental data. One of the most important findings of this work is that the component of the S(q) vs. q plot representing intramolecular contributions in a fully deuterated cis -1,4-PB sample exhibits a monotonic decrease with q which remains completely unaffected by the pressure. In contrast, the intermolecular contribution exhibits a distinct peak (at around 1.4 Ĺ,1) whose position shifts towards higher q values as the pressure is raised, accompanied by a decrease in its intensity. 3D view of the simulation box containing 32 chains of C128cis -1,4-polybutadiene at density ,,=,0.849 g,·,cm,3 and the conformation of a single C128cis -1,4-PB chain fully unwrapped in space. [source] Structure determination of oligomeric alkannin and shikonin derivativesBIOMEDICAL CHROMATOGRAPHY, Issue 7 2005Apostolos Spyros Abstract Monomeric alkannin and shikonin (A/S) are potent pharmaceutical substances with a wide spectrum of biological activity and comprise the active ingredients for several pharmaceutical preparations. Therefore, the determination of the impurities, degradation products or byproducts in alkannin and shikonin samples is of great importance. Oligomeric alkannin and shikonin are formed during biosynthesis of these bioactive secondary metabolites in Boraginaceaous root plants, during tissue culture production of A/S, during alkaline hydrolysis of A/S esters and also thermal treatment of A/S. In the present study, a dimeric alkannin/shikonin compound was isolated by size exclusion chromatography from alkannin and shikonin commercial samples and its structure was determined by one- and two-dimensional NMR spectroscopy. The structure of the most abundant oligomeric species in these samples, a dimeric naphthoquinone, was established for the ,rst time, indicating that coupling of the side chain of one naphthoquinone unit with the aromatic ring of a second naphthoquinone leads to dimer formation. This type of coupling allows further oligomerization by leaving one isohexenyl side chain available at the second monomer unit. Copyright © 2005 John Wiley & Sons, Ltd. [source] Biodegradation of poly(tetramethylene succinate-cotetramethylene abdicate) and poly(tetramethylene succinate) through water-soluble productsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2001Eiichi Kitakuni Abstract Poly(tetramethylene succinate-co-tetramethylene adipate) (PBSA) and poly(tetramethylenesuccinate) (PBS) were hydrolyzed experimentally into water-soluble oligomers and monomers by Chromobacterium extracellular lipase. The oligomers were identified by high-performance liquid chromatography,mass spectrometry and 1H-nuclear magnetic resonance, which indicated that a total of 28 oligomer species were liberated from PBSA, and that 13 of them were identical to the hydrolysates from PBS. Moreover, 20 of the species were polyester-based compounds of monomer units, and the other 8 species were small amounts of diurethane compounds. Bis(hydroxybutyl) succinate (BSB) and bis(hydroxybutyl) hexamethylene dicarbamate (BHB) were the typical oligomers and were chemically synthesized. Biodegradability of BSB and BHB was examined for 28 d in the activated sludge, and analysis of the results of this study indicated that the final conversion rate of constituent carbon to carbon dioxide was estimated at 80 mol% for BSB and 10 mol% for BHB. The remaining amount of carbon in the undegraded BHB was 20 mol%. In the presence of BSB, the biodegradability of BHB was increased by about 1.5 times. The suggestion was made that BSB induced a growth of microorganisms and helped BHB degradation. This is consistent with the observation that the biodegradation of BHB in native soil for 60 d reached > 60%. [source] Synthesis of Components for the Generation of Constitutional Dynamic Analogues of Nucleic AcidsHELVETICA CHIMICA ACTA, Issue 1 2008David Abstract The introduction of dynamic covalent polymers, in which the monomer units are linked by reversible covalent bonds and can undergo component exchange, opens up new possibilities for the generation of functional materials. Extending this approach to the generation of dynamic biopolymers in aqueous media, which are able to adapt constitution (sequence, length) to external factors (e.g., environment, medium, template), would provide an alternative approach to the de novo design of functional dynamic bio-macromolecules. As a first step towards this goal, various mono- and bifunctionalised (hetero- and homotopic) nucleic acid-derived building blocks of type I,X have been synthesised for the generation of dynamic main-chain and side-chain reversible nucleic acid analogues. Hydrazide- and/or acetal (protected carbonyl)-functionalised components were selected, which differ in terms of flexibility, length, net formal charge, and hydrazide/acetal substituents, in order to explore how such factors may affect the properties (structure, solubility, molecular recognition features) of the polymer products that may be generated by polycondensation. [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] Living cationic polymerization of amide-functional vinyl ethers: Specific properties of SnCl4 -based initiating systemJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2008Motomasa Yonezumi Abstract Living cationic copolymerization of amide-functional vinyl ethers with isobutyl vinyl ether (IBVE) was achieved using SnCl4 in the presence of ethyl acetate at 0 °C: the number,average molecular weight of the obtained polymers increased in direct proportion to the monomer conversion with relatively low polydispersity, and the amide-functional monomer units were introduced almost quantitatively. To optimize the reaction conditions, cationic polymerization of IBVE in the presence of amide compounds, as a model reaction, was also examined using various Lewis acids in dichloromethane. The combination of SnCl4 and ethyl acetate induced living cationic polymerization of IBVE at 0 °C when an amide compound, whose nitrogen is adjacent to a phenyl group, was used. The versatile performance of SnCl4 especially for achieving living cationic polymerization of various polar functional monomers was demonstrated in this study as well as in our previous studies. Thus, the specific properties of the SnCl4 initiating system are discussed by comparing with the EtxAlCl3,x systems from viewpoints of hard and soft acids and bases principle and computational chemistry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6129,6141, 2008 [source] Synthesis of comb-like polystyrene with poly(N -phenyl maleimide- alt-p -chloromethyl styrene) as macroinitiatorJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2006Yan Shi Abstract The copolymerization of N -phenyl maleimide and p -chloromethyl styrene via reversible addition,fragmentation chain transfer (RAFT) process with AIBN as initiator and 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N -phenyl maleimide- alt - p -chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2,-bipyridine, well-defined comb-like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069,2075, 2006 [source] Characterization of ring-opening polymerization of genipin and pH-dependent cross-linking reactions between chitosan and genipinJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2005Fwu-Long Mi Abstract In this study, a novel chitosan-based polymeric network was synthesized by crosslinking with a naturally occurring crosslinking agent,genipin. The results showed that the crosslinking reactions were pH-dependent. Under basic conditions, genipin underwent a ring-opening polymerization prior to crosslinking with chitosan. The crosslink bridges consisted of polymerized genipin macromers or oligomers (7 , 88 monomer units). This ring-opening polymerization of genipin was initiated by extracting proton from the hydroxyl groups at C-1 of deoxyloganin aglycone, followed by opening the dihydropyran ring to conduct an aldol condensation. At neutral and acidic conditions, genipin reacted with primary amino groups on chitosan to form heterocyclic amines. The heterocyclic amines were further associated to form crosslinked networks with short chains of dimmer, trimer, and tetramer bridges. An accompanied reaction of nucleophilic substitution of the ester group on genipin by the primary amine group on chitosan would occur in the presence of an acid catalysis. The extent in which chitosan gels crosslinked with genipin was significantly dependent on the crosslinking pH values: 39.9 ± 3.8% at pH 5.0, 96.0 ± 1.9% at pH 7.4, 45.4 ± 1.8% at pH 9.0, and 1.4 ± 1.0% at pH 13.6 (n = 5, p < 0.05). Owing to the different crosslinking extents and different chain lengths of crosslink bridges, the genipin-crosslinked chitosan gels showed significant difference in their swelling capability and their resistance against enzymatic hydrolysis, depending on the pH conditions for crosslinking. These results indicated a direct relationship between the mode of crosslinking reaction, and the swelling and enzymatic hydrolysis properties of the genipin-crosslinked chitosan gels. The ring-opening polymerization of genipin and the pH-dependent crosslinking reactions may provide a novel way for the preparation and exploitation of chitosan-based gels for biomedical applications. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1985,2000, 2005 [source] Synthesis and characterization of poly[phenyl(fluoroalkyloxaalkane)silanediyl]sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2003Vjacheslav V. Zuev Abstract Monomeric fluoroalkoxyalkyl(phenyl)dichlorosilanes were synthesized with quantitative yields by hydrosilylation of allyl ethers of fluoroalcohols with phenyldichlorosilane with Pt(Ph3Sb)2Cl2 complex as a catalyst. Starting from these monomers, corresponding polysilanes with weight-average molecular weights of 2,3 × 104 were obtained by the Wurtz reaction. Increasing the CF2 groups containing two to six monomer units caused the char yields to increase from 3 to 48% at 800 °C in air. The emission characteristics of these polysilanes in a chloroform solution were examined. They had a narrow peak at 344 nm with a small Stokes shift (,20 nm). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3761,3767, 2003 [source] Synthesis of branched polypropylene with isotactic backbone and atactic side chains by binary iron and zirconium single-site catalystsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2003Zhibin Ye Abstract This article reports the use of a binary single-site catalyst system for synthesizing comb-branched polypropylene samples having isotactic polypropylene (iPP) backbones and atactic polypropylene (aPP) side chains from propylene feedstock. This catalyst system consisted of the bisiminepyridine iron catalyst {[2-ArNC(Me)]2C5H3N}FeCl2 [Ar = 2,6-C6H3(Me)2] (1) and the zirconocene catalyst rac -Me2Si(2-MeBenz[e]Ind)2ZrCl2 (2). The former in situ generated 1-propenyl-ended aPP macromonomer, whereas the latter incorporated the macromonomer into the copolymer. The effects of reaction conditions, such as the catalyst addition procedure and the ratio of 1/2 on the branching frequency, were examined. Copolymer samples having a branching density up to 8.6 aPP side chains per 1000 iPP monomer units were obtained. The branched copolymers were characterized by 13C NMR and differential scanning calorimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1152,1159, 2003 [source] Enzymatic Hydrolysis of , - and , -Oligo(L -aspartic acid)s by Poly(aspartic acid) Hydrolases-1 and 2 from Sphingomonas sp.MACROMOLECULAR BIOSCIENCE, Issue 3 2004Abstract Summary: The enzymatic hydrolysis of , - and , -oligo(L -aspartic acid)s by PAA hydrolase-1 and PAA hydrolase-2 (purified from Sphingomonas sp. KT-1) was performed to elucidate the mechanism of the microbial degradation by Sphingomonas sp. KT-1 of the thermally synthesized ,,, -poly(D,L -aspartic acid) (tPAA). GPC analysis of the hydrolyzed products of , - and , -tetra(L -aspartic acid)s by PAA hydrolase-1 has showed that PAA hydrolase-1 is capable of hydrolyzing only the specific amide bonds between , -aspartic acid units. The RP-HPLC analysis of the enzymatic hydrolysis of , -oligo(L -aspartic acid)s (4 and 5 mers) by PAA hydrolase-1 has suggested that the enzymatic hydrolysis of , -oligo(L -aspartic acid)s occurs via an endo-mode cleavage. In contrast, PAA hydrolase-2 hydrolyzed both , - and , -oligo(L -aspartic acid)s via an exo-mode cleavage to yield L -aspartic acid as a final product. A kinetic study on the enzymatic hydrolysis of , -oligo(L -aspartic acid)s (3 to 7 mers) by PAA hydrolase-2 has indicated that Km values are almost independent of the number of monomer units in oligomers of 4 to 7 mers, while that Vmax values are markedly dependent on the chain length and show a maximum value at 5 mer. A proposed mechanism of the enzymatic hydrolysis of tPAA by PAA hydrolase-1 and PAA hydrolase-2 in the cell of Sphingomonas sp. KT-1. [source] Synthesis and Characterization of Poly(N -vinylimidazole- co -acrylonitrile) and Determination of Monomer Reactivity RatiosMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2004Nursel Pekel Abstract Summary: Radical-initiated solution copolymerization of N -vinylimidazole (VIM) and acrylonitrile (AN) was carried out with 2,2, -azobisisobutyronitrile (AIBN) as an initiator in benzene at 70,°C in nitrogen atmosphere. The structure and composition of synthesized copolymers for a wide range of monomer feeds were determined by FTIR, 1H and 13C NMR spectroscopy with the aid of recorded analytical absorption bands for VIM (667 cm,1, CN of imidazole ring) and AN (2,242 cm,1, CN group), as well as by using the areas of proton and carbon atom signals from corresponding functional groups of monomer units. Monomer reactivity ratios for VIM (M1)-AN (M2) pair were determined by nonlinear regression (NLR), Kelen,Tüdös (KT) and Fineman,Ross (FR) methods. They were found to be r1,=,0.24 and r2,=,0.15 for the NLR method, r1,=,0.22 and r2,=,0.094 for the KT method, and r1,=,0.24 and r2,=,0.12 for the FR method, respectively. The relatively high activity observed of VIM growing macroradical and the results of FTIR and 1H NMR structural analysis of copolymers suggest the formation of complexed linkages between monomers and growing radicals in chain propagation reactions. Similar complexation between monomer,comonomer units in the structure of formed macromolecules showed an increase in isotactic triad fractions in the copolymer. Complex formation between the imidazole ring and nitrile group in both the monomer mixture and chain growing reactions. [source] A New View of the Anionic Diene Polymerization MechanismMACROMOLECULAR SYMPOSIA, Issue 1 2004A.Z. Niu Abstract We investigated the anionic polymerization of butadiene in d-heptane solvent using tert -butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: 1H NMR and small angle neutron scattering (SANS). The time resolved 1H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator --- at about 10% monomer conversion --- signals the onset of the normal ,6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non-polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining 1H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large-scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with Nagg >>1000 and Rg , 1000Ĺ were found. [source] Self-Assembly of Rod-Like Copolymers into Monolayers: A Simple Theoretical Estimate of Molecular Recognition QualityMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7-8 2008Anatoly V. Berezkin Abstract A discrete model of a monolayer, consisting of identical rod-like copolymer molecules, is suggested. The influence of the copolymer's composition and sequence on its self-assembly was studied. Thermodynamic quantities of monolayers were calculated. It is shown that the system undergoes an "order-disorder" transition upon temperature increase. The most regular monolayers are formed by copolymers with quasi-random sequences. Nevertheless, the monomer composition of such "good" sequences can vary over a wide range. It is shown that homopolymers, copolymers with a predominance of one-type monomer units and copolymers consisting of a small number of large blocks have a reduced ability to self-assembly. [source] Synthesis and monomer reactivity ratios of ethyl ,-acetoxyacrylate and acrylic acid copolymersPOLYMER INTERNATIONAL, Issue 11 2005Cédric Loubat Abstract The synthesis of ethyl ,-acetoxyacrylate (EAA) and the study of its radical polymerization is described. We report the monomer reactivity ratios for copolymers of EAA and acrylic acid (AA) using three different methods: the Jaacks, the Macret and the Fineman,Ross methods. Copolymers were obtained by free radical polymerization initiated by 2,2,-azobisisobutyronitrile in acetonitrile solutions and were analyzed by NMR and HPLC. The HPLC analysis was used to determine the molar fractions of EAA and AA in the copolymers. The reactivity ratios were estimated to be close to 1 for each monomer. Thus, copolymers of poly(acrylic acid) bearing some biodegradable units of EAA in the chain were subsequently prepared. The study of the hydrolysis of these units shows that only basic conditions were efficient to lead to hydrolyzed monomer units. Copyright © 2005 Society of Chemical Industry [source] Blood cell separation using crosslinkable copolymers containing N,N -dimethylacrylamidePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2007Shizue Hayashi Natori Abstract Amphiphilic copolymers using hydrophilic N,N -dimethylacrylamide (DMA), hydrophobic methyl methacrylate (MMA) and a crosslinkable monomer, 3-methacryloyloxypropyl trimethoxysilane (MTSi), were synthesized and evaluated as coating materials for leukocyte removal filters for whole blood. When filters composed of non-woven fabrics were coated with crosslinked synthesized copolymers, the elution ratios of the copolymers to water were adequately low because of the crosslinking with trimethoxysilane groups of MTSi units in the copolymers. Filters coated with crosslinked poly(DMA- co -MTSi) having a 0.96 mole fraction of DMA units showed a 0.35,±,0.44% platelet permeation ratio and a logarithmic reduction of 4.0,±,0.68 for leukocytes. On the other hand, an increase in the content of MMA units in the DMA-containing copolymers improved the permeation ratio of the platelets dramatically. Filters coated with crosslinked poly(DMA- co -MMA- co -MTSi) containing a 0.39 mole fraction of MMA units and a 0.58 mole fraction of DMA units showed an 86,±,3.0% platelet permeation ratio and a logarithmic reduction of 2.1,±,1.2 for leukocytes. This indicates that an adequate content of hydrophobic monomer units, such as MMA units, is necessary for effective platelet permeation. Copyright © 2007 John Wiley & Sons, Ltd. [source] Molecular Self-Recognition: Rotational Spectra of the Dimeric 2-Fluoroethanol ConformersCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2009Xunchen Liu Abstract Fluoroalcohols show competitive formation of intra- and intermolecular hydrogen bonds, a property that may be crucial for the protein-altering process in a fluoroalcohol/water solution. In this study, we examine the intra- and intermolecular interactions of 2-fluoroethanol (FE) in its dimeric conformers by using rotational spectroscopy and ab initio calculations. Three pairs of homo- and heterochiral dimeric FE conformers are predicted to be local minima at the MP2/6-311++G(d,p) level of theory. They are solely made of the slightly distorted most stable G+g,/G,g+ FE monomer units. Jet-cooled rotational spectra of four out of the six predicted dimeric conformers were observed and unambiguously assigned for the first time. All four observed dimeric conformers have compact geometries in which the fluoromethyl group of the acceptor tilts towards the donor and ensures a large contact area. Experimentally, the insertion of the OH group of one FE subunit into the intramolecular OH,,,F bond of the other was found to lead to a higher stabilisation than the pure association through an intermolecular OH,,,OH link. The hetero- and homochiral combinations were observed to be preferred in the inserted and the associated dimeric conformers, respectively. The experimental rotational constants and the stability ordering are compared with the ab initio calculations at the MP2 level with the 6-311++G(d,p) and aug-cc-pVTZ basis sets. The effects of fluorination and the competing inter- and intramolecular hydrogen bonds on the stability of the dimeric FE conformers are discussed. [source] | |||||||||||||