Polydispersity

Distribution by Scientific Domains

Kinds of Polydispersity

  • low polydispersity
  • narrow polydispersity

  • Terms modified by Polydispersity

  • polydispersity index
  • polydispersity index value

  • Selected Abstracts


    Analysis of scattering from polydisperse structure using Mellin convolution

    JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2006
    Norbert Stribeck
    This study extends a mathematical concept for the description of heterogeneity and polydispersity in the structure of materials to multiple dimensions. In one dimension, the description of heterogeneity by means of Mellin convolution is well known. In several papers by the author, the method has been applied to the analysis of data from materials with one-dimensional structure (layer stacks or fibrils along their principal axis). According to this concept, heterogeneous structures built from polydisperse ensembles of structural units are advantageously described by the Mellin convolution of a representative template structure with the size distribution of the templates. Hence, the polydisperse ensemble of similar structural units is generated by superposition of dilated templates. This approach is particularly attractive considering the advantageous mathematical properties enjoyed by the Mellin convolution. Thus, average particle size, and width and skewness of the particle size distribution can be determined from scattering data without the need to model the size distributions themselves. The present theoretical treatment demonstrates that the concept is generally extensible to dilation in multiple dimensions. Moreover, in an analogous manner, a representative cluster of correlated particles (e.g. layer stacks or microfibrils) can be considered as a template on a higher level. Polydispersity of such clusters is, again, described by subjecting the template structure to the generalized Mellin convolution. The proposed theory leads to a simple pathway for the quantitative determination of polydispersity and heterogeneity parameters. Consistency with the established theoretical approach of polydispersity in scattering theory is demonstrated. The method is applied to the best advantage in the field of soft condensed matter when anisotropic nanostructured materials are to be characterized by means of small-angle scattering (SAXS, USAXS, SANS). [source]


    A Bimetallic Ruthenium Complex as a Catalyst Precursor for the Atom Transfer Radical Polymerization of Methacrylates at Ambient Temperature

    ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2006
    Michel Haas
    Abstract The bimetallic ruthenium complex [(1,3,5- i -Pr3C6H3)Ru(,-Cl)3RuCl(C2H4)(PCy3)] has been synthesized by reaction of [(1,3,5- i -Pr3C6H3)RuCl2)]2 with one equivalent of PCy3 in the presence of ethylene. It can be used as a catalyst precursor for the controlled atom transfer radical polymerization of methacrylates at 35,C. The resulting polymers show low polydispersities. [source]


    Effect of initiator type and concentration on polymerization rate and molecular weight in the bimolecular nitroxide-mediated radical polymerization of styrene

    ADVANCES IN POLYMER TECHNOLOGY, Issue 1 2010
    Telma Regina Nogueira
    Abstract To increase the polymerization rate in the bimolecular nitroxide-mediated radical polymerization (NMRP) of styrene, without using expensive non-commercial reagents, an experimental study using 2,2,6,6-tetramethyl-1-piperidinoxyl as a controller and tert-butylperoxy 2-ethylhexyl carbonate (TBEC) as the initiator was carried out. The basis for comparison was the bimolecular NMRP of styrene with dibenzoyl peroxide as initiator. It was found that faster polymerization rates and still relatively low polydispersities were possible using TBEC. 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:11,19, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20170 [source]


    Characterization of pegylated copolymeric micelles and in vivo pharmacokinetics and biodistribution studies

    JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2006
    Wen-Jen Lin
    Abstract The aim of this study was to evaluate the influence of pegylated copolymeric micelle carrier on the biodistribution of drug in rats. The copolymers were synthesized via a modified ring-opening copolymerization of lactone monomers (,-caprolactone, ,-valerolactone, L -lactide) and poly(ethylene glycol) (PEG10,000 and PEG4000). The molecular weights and the polydispersities of synthesized copolymers were in the range of 15,000,31,000 g/mol and 1.7,2.7, respectively. All of the pegylated amphiphilic copolymers were micelles formed with low CMC values in the range of 10,7,10,8M. The drug-loaded micelles were prepared via a dialysis method. The average particle size of micelles was around 150,200 nm. The cytotoxicity in terms of cell viability after treated with PCL,PEG, PVL,PEG, and PLA,PEG micelles was insignificant. PCL,PEG and PVL,PEG micelles without branch side chain in structures had higher drug loading than PLA,PEG micelles. In vitro release profiles indicated the release of indomethacin from these micelles exhibited a sustained release behavior. The similar phenomenon was also observed in vivo in rats. The pegylated copolymeric micelles not only decreased drug uptake by the liver and kidney, but also prolonged drug retention in the blood. 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]


    Swelling and polymer erosion for poly(ethylene oxide) tablets of different molecular weights polydispersities

    JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2010
    Anna Krner
    Abstract The aim of the study was to determine and compare the degree of swelling and the swelling kinetics of poly(ethylene oxide) (PEO) hydrophilic matrix tablets without any additives for matrixes with different molecular weight polydispersities. A wide range of "mixed" polydisperse PEO tablets were obtained by mixing two PEO batches with average molecular weights of 105 and 2,,106, respectively. These were compared with "single-batch" tablets with narrower mono-modal molecular weight distributions. A texture analyzer (TA) was used to determine, during the entire dissolution process, the thickness of the "gel" layer, the height of the dry tablet core and the total height of the tablet. The release of polymer from the tablet was also measured using a chromatographic method. Both the swelling histories and the polymer release rates varied strongly with molecular weight and agitation rate, whereas the rate of dissolution of the solid core varied much less with molecular weight. For single-batch and mixed tablets, tuned to give the same release rate, the swelling process was found to be very similar, regardless of the molecular polydispersity (between 1.2 and 8.8). These results support a previously proposed dissolution model with the key assumption of a constant critical viscosity, independent of time or polymer molecular weight, at the surface of the gel layer of a dissolving tablet. 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1225,1238, 2010 [source]


    Solution, thermal and optical properties of novel poly(pyridinium salt)s derived from conjugated pyridine diamines,

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2010
    Alexi K. Nedeltchev
    Abstract Several novel poly(pyridinium salt)s with heterocyclic pyridine moieties in their backbones with tosylate and triflimide counterions were prepared by either ring-transmutation polymerization reaction of phenylated-bis(pyrylium tosylate) with isomeric pyridine diamines of 4-phenyl-2,6-bis(4-aminophenyl)pyridine in dimethyl sulfoxide (DMSO) for 48 h at 130,140 C or by metathesis reaction of the respective tosylate polymers with lithium triflimide in DMSO at about 60 C. Their chemical structures were characterized by FTIR, 1H, 13C NMR spectroscopy, and elemental analysis. Their number-average molecular weights (Mn) were in the range of 8,000,51,000 and their polydispersities in the range of 1.18,2.13 as determined by gel permeation chromatography. They had excellent thermal stabilities of 340,458 C and high glass transition temperatures >200 C. As they showed good solubilities in common organic solvents, their solution properties were also characterized for their lyotropic liquid-crystalline properties with polarizing optical microscopy (POM) studies. Their photoluminescent properties were examined by using a spectrofluorometer in both solution and solid states. Their quantum yields were rather low, which were in the range of 1.3,2.0%. Additionally, hand-drawn fibers from the melts were examined to determine their morphologies with a number of microscopic techniques including POM, scanning electron microscopy, and transmission electron microscopy. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source]


    Facile syntheses, morphologies, and optical absorptions of P3HT coil-rod-coil triblock copolymers

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2010
    Herman Lim
    Abstract Here we report syntheses, photophysical properties, and morphologies of a series of coil-rod-coil ABA triblock copolymers containing highly regioregular poly(3-hexylthiophene) (P3HT) as the central rod block. A new methodology, based on the coupling reaction between living polymeric anions [polystyrene, polyisoprene, and poly(methyl methacrylate)] and aldehyde terminated P3HT, was successfully developed to synthesize the triblock copolymers with low polydispersities. This coupling reaction was effective for building blocks with a variety of molecular weights; therefore, a good variation in compositions of the triblock copolymers could be feasibly achieved. The non-P3HT coil segments and the solvents were found to exhibit noticeable effects on morphologies of the spin-coated thin films. Attachment of the coil segments to P3HT did not change the optical absorption of the P3HT segment as the block copolymers were dissolved in solution regardless the chemical structure and the molecular weight of the coil segment. Interestingly, different UV,vis absorption behaviors were observed for the spin-coated thin films of the block copolymers, which closely related to their morphologies. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3311,3322, 2010 [source]


    Water-soluble triply-responsive homopolymers of N,N -dimethylaminoethyl methacrylate with a terminal azobenzene moiety

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2010
    Xinde Tang
    Abstract Novel water-soluble triply-responsive homopolymers of N,N -dimethylaminoethyl methacrylate (DMAEMA) containing an azobenzene moiety as the terminal group were synthesized by atom transfer radical polymerization (ATRP) technique. The ATRP process of DMAEMA was initiated by an azobenzene derivative substituted with a 2-bromoisobutyryl group (Azo-Br) in the presence of CuCl/Me6TREN in 1,4-dioxane as a catalyst system. The molecular weights and their polydispersities of the resulting homopolymers (Azo-PDMAEMA) were characterized by gel permeation chromatography (GPC). The homopolymers are soluble in aqueous solution and exhibit a lower critical solution temperature (LCST) that alternated reversibly in response to Ph and photoisomerization of the terminal azobenzene moiety. It was found that the LCST increased as pH decreased in the range of testing. Under UV light irradiation, the trans -to- cis photoisomerization of the azobenzene moiety resulted in a higher LCST, whereas it recovered under visible light irradiation. This kind of polymers should be particularly interesting for a variety of potential applications in some promising areas, such as drug controlled-releasing carriers and intelligent materials because of the multistimuli responsive property. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2564,2570, 2010 [source]


    Synthesis of comb polymers via grafting-onto macromolecules bearing pendant diene groups via the hetero-Diels-Alder-RAFT click concept

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2010
    Antoine Bousquet
    Abstract Comb polymers were synthesized by the "grafting-onto" method via a combination of Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization and the hetero-Diels-Alder (HDA) cycloaddition. The HDA reactive monomer trans, trans-hexa-2,4-dienylacrylate (ttHA) was copolymerized with styrene via the RAFT process. Crosslinking was minimized by decreasing the monomer concentration,whilst keeping monomer to polymer conversions low,resulting in reactive backbones with on average one reactive pendant diene groups for 10 styrene units. The HDA cycloaddition was performed between the diene functions of the copolymer and a poly(n -butyl acrylate) (PnBA) prepared via RAFT polymerization with pyridin-2-yldithioformate, which can act as a dienophile. The coupling reactions were performed within 24 h at 50 C and the grafting yield varies from 75% to 100%, depending on the number average molecular weight of the PnBA (3500 g mol,1 < Mn < 13,000 g mol,1) grafted chain and the reaction stoichiometry. The molecular weights of the grafted block copolymers range from 19,000 g mol,1 to 58,000 g mol,1 with polydispersities close to 1.25. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1773,1781, 2010 [source]


    Cyclic alkoxyamines for nitroxide-mediated radical polymerization

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2008
    Jean Ruehl
    Abstract A 5-membered cyclic alkoxyamine and a 17-membered cyclic alkoxyamine were synthesized and used in the polymerization of styrene. Polymerizations using the 5-membered cyclic alkoxyamine resulted in polymers with uncontrolled molecular weights and high polydispersities. Polymerizations using the 17-membered cyclic alkoxyamine produced oligomeric polymers in which multiple polymer chains are linked through NO-C bonds. EPR homolysis experiments revealed that the 5-membered cyclic alkoxyamine does not dissociate to form a nitroxide species, even at temperatures as high as 403 K. In contrast, the 17-membered cyclic alkoxyamine does dissociate to form nitroxide, but the rate of dissociation is slower than that of parent acyclic alkoxyamine 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8049,8069, 2008 [source]


    Cyclometalated 2-phenylpyridine complex [RuII(o -C6H4 -py)(MeCN)4]PF6 as a tunable catalyst for living radical polymerization

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2008
    F. Diaz Camacho
    Abstract The cyclometalated complex [RuII(o -C6H4 -py)(MeCN)4]PF6 (1) with a ,-RuC bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n -butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2-bromoisobutyrate, methyl 2-bromopropionate, and 1-phenylethyl bromide. The polymerization requires the presence of Al(OiPr)3 and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)3 and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl2 as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion-dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst (1), when the added amount of (1) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the (1)-catalyzed polymerization are discussed. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193,4204, 2008 [source]


    Synthesis of crosslinkable fluorinated polyesters for optical waveguide devices

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2007
    Xu Fei
    Abstract A series of novel crosslinkable, highly fluorinated polyesters were synthesized by copolycondensation reactions of terephthaloyl chloride with 4, 4,-(hexafluoroisopropy-lidene)-diphenol and 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-octane-1,8-diol, followed by reaction with 2-hydroxyethyl methacrylate. The resulting polyesters with the molecular weights (Mn: 12,100,20,000 g mol,1) and polydispersities (1.49,2.25) were useful for the fabrication of polymer optical devices because of their good solubility in common organic solvent and the processable flexibility. The ratios of the components of the polyesters were characterized by FTIR and NMR. The polyesters had high glass transition temperature (Tg,: up to 170 C) and good thermal stabilities (Td: up to 470 C). The refractive index of the polyester film was tuned and controlled in the range of 1.447,1.576 at 1550 nm by monitoring the component fractions during the preparation procedures. Low-loss optical waveguides were fabricated from the resulting polyesters and the propagation loss of the channel waveguides was measured to be around 0.56 dB/cm at 1550 nm. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5923,5931, 2007 [source]


    Titanium and zirconium complexes containing modified TREN ligands for the polymerization of 1-alkenes,A comparative study

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007
    Padmanabhan 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]


    Homogeneous phase polymerization of vinylidene fluoride in supercritical carbon dioxide

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007
    Sabine Beuermann
    Abstract For the first time, stabilizer-free vinylidene fluoride (VDF) homopolymerizations were carried out in homogenous phase with supercritical CO2 using the conventional initiator di- tert butyl peroxide (DTBP). In-line FT-NIR spectroscopy showed that complete monomer conversion may be obtained. Molecular weights were determined via size-exclusion chromatography and polymer endgroup analysis by 1H-NMR spectroscopy. The number average molecular weights were below 104 g mol,1 and polydispersities ranged from 3.1 to 5.7 depending on DTBP and VDF concentration. For allowing isothermal reaction, high CO2 contents ranging from 61 to 83 wt % were used. The high-temperature and high-pressure conditions required for homogeneous polymerization did not alter the amount of defects in VDF chaining. Scanning electron microscopy indicated that regular stack-type particles are obtained upon expansion of the homogeneous polymerization mixture. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5626,5635, 2007 [source]


    Copolymerizations of butyl methacrylate and fluorinated methacrylates via RAFT miniemulsion polymerization

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2007
    Tian-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]


    Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry investigations of polystyrene and poly(methyl methacrylate) produced by monoacylphosphine oxide photoinitiation

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2007
    Faith J. Wyzgoski
    Abstract The chain-end-group composition was determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analyses of low-molecular-weight polystyrene (PS) and poly(methyl methacrylate) (PMMA) produced by free-radical polymerization with a monoacylphosphine oxide, (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO), as a photoinitiator. Gel permeation chromatography (GPC) fractionation of the PS and PMMA samples with initial polydispersities of 1.81 and 2.81, respectively, yielded improved MALDI-TOF MS spectra. Spectral analyses of the PS fractions showed distributions attributable to PS having two diphenylphosphinyl ends and PS having one diphenylphosphinyl end and/or one 2,4,6-trimethylbenzoyl end, indicating that a combination of PS radicals with the highly reactive diphenylphosphine oxide group at one end of the chains was the predominant mode of termination. MALDI-TOF MS results for PMMA fractions provided evidence for termination primarily by disproportionation, but structure determination was confounded by the presence of isobaric peaks. Discernible peaks were obtained by MALDI-TOF MS analyses of GPC fractions of TPO-initiated poly(methyl- d3 methacrylate- d5), in which the major product was PMMA with a diphenylphosphinyl end group and an abstracted deuterium end group, whereas the minor combination product had two diphenylphosphinyl chain ends. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2161,2171, 2007 [source]


    A variety of poly(m -benzamide)s with low polydispersities from inductive effect-assisted chain-growth polycondensation

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2006
    Tomoyuki Ohishi
    Abstract Chain-growth polycondensation of 3-(alkylamino)benzoic acid alkyl esters 1 was investigated for obtaining poly(m -benzamide)s with defined molecular weights and low polydispersities. Polymerization conditions were first studied to find that ethyl 3-(octylamino)benzoate (1b) polymerized in a chain polymerization manner in the presence of lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a base and phenyl 4-methylbenzoate (2b) as an initiator in THF at 0 C. The molecular weight of the polymer was controlled by the feed ratio of monomer to initiator. The polymerization of 1c,i with a variety of N -alkyl groups was then carried out under the established conditions to yield well-defined poly(m -benzamide)s, which showed higher solubility than those of the corresponding poly(p -benzamide)s. Furthermore, the 4-octyloxybenzyl group on the amide nitrogen in poly1i was removed by treatment with trifluoroacetic acid (TFA) to give N -unsubstituted poly(m -benzamide) (poly1j) with a low polydispersity, which is soluble in DMAc and DMSO, contrary to the para-substituted counterpart. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4990,5003, 2006 [source]


    Dendrimer-star polymer and block copolymer prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization with dendritic chain transfer agent

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2005
    Chun-Yan Hong
    Abstract A new reversible addition-fragmentation chain transfer (RAFT) agent, dendritic polyester with 16 dithiobenzoate terminal groups, was prepared and used in the RAFT polymerization of styrene (St) to produce star polystyrene (PSt) with a dendrimer core. It was found that this polymerization was of living characters, the molecular weight of the dendrimer-star polymers could be controlled and the polydispersities were narrow. The dendrimer-star block copolymers of St and methyl acrylate (MA) were also prepared by the successive RAFT polymerization using the dendrimer-star PSt as macro chain transfer agent. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6379,6393, 2005 [source]


    Cyclic poly(pyridine ether)s by the polycondensation of 2,6-difluoropyridine with various diphenols

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2005
    Hans R. Kricheldorf
    Abstract The bistrimethylsilyl derivatives of six different diphenols were polycondensed with 2,6-difluoropyridine in N -methylpyrrolidone in the presence of K2CO3. On the basis of previous studies, the reaction conditions were optimized for almost quantitative conversions. The feed ratio was systematically varied to optimize the molecular weight. A 2 mol % excess of 2,6-difluoropyridine was needed to obtain maximum molecular weights. In the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra of the optimized polyethers, only cycles were found (detectable up to 5000 Da). Obviously, the relatively low molecular weights obtained under optimized conditions resulted from a limitation of the chain growth by cyclization, indicating a high cyclization tendency for poly(pyridine ether)s. The size exclusion chromatography measurements not only proved low molecular weights but also demonstrated the existence of bimodal mass distributions and high polydispersities. Protonation of the poly(pyridine ether)s required strong acids such as methane or trifluoromethane sulfonic acid. The solubilities of the neutral and protonated polyethers derived from bisphenol A were studied in various solvents. The MALDI-TOF mass spectra proved that protonation at 20,25 C did not cause cleavage of ether bonds. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4781,4789, 2005 [source]


    Nitroxide-mediated homo- and block copolymerization of styrene and multifunctional acryl- and methacryl derivatives

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005
    Meizhen Yin
    Abstract The ability of different alkoxyamines (I1, I2, I3, I4, and I5) to initiate controlled radical polymerization of styrene was evaluated. Among them, 2-hydroxymethyl-2-[(2-methyl-1-phenyl-propyl)-(1-phenyl-ethoxy)-amino]-propane-1,3-diol (I5) gave the highest polymerization rate of styrene, and the best control over the molecular weight and the molecular weight distribution of polystyrene. Kinetic studies confirmed that with initiator I5 the polymerization of styrene proceeded in a controlled way. The controlled radical homopolymerization of multifunctional acryl- and methacryl derivatives using initiator I5 could not be realized as demonstrated by the high polydispersities (PD) obtained. However, it was possible to polymerize multifunctional acryl- and methacryl derivatives using a polystyrene macroinitiator (Pst) and, thus, novel amphiphilic block copolymers with a narrow molecular weight distribution were obtained. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1873,1882, 2005 [source]


    Ambient-temperature copper-catalyzed atom transfer radical polymerization of methacrylates in ethylene glycol solvents

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2005
    Solomon 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]


    Syntheses of cyclic polycarbonates by the direct phosgenation of bisphenol M,

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2005
    Hans R. Kricheldorf
    Abstract Bisphenol M was subjected to interfacial polycondensations in an NaOH/CH2Cl2 system with triethylamine as a catalyst. Regardless of the catalyst concentration, similar molecular weights were obtained, and matrix-assisted laser desorption/ionization time-of-flight mass spectra exclusively displayed mass peaks of cycles (detectable up to 15,000 Da). With triethyl benzyl ammonium chloride as a catalyst, linear chains became the main products, but the contents of the cycles and the molecular weights strongly increased with higher catalyst/bisphenol ratios. When the pseudo-high-dilution method was applied, both diphosgene and triphosgene yielded cyclic polycarbonates of low or moderate molecular weights. Size exclusion chromatography measurements, evaluated with the triple-detection method, yielded bimodal mass distribution curves with polydispersities of 5,12. Furthermore, a Mark,Houwink equation was elaborated, and it indicated that the hydrodynamic volume of poly(bisphenol M carbonate) was quite similar to that of poly(bisphenol A carbonate)s with similar concentrations of cyclic species. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1248,1254, 2005 [source]


    Dendrimers as scaffolds for multifunctional reversible addition,fragmentation chain transfer agents: Syntheses and polymerization

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004
    Xiaojuan 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]


    Synthesis and properties of biomimetic poly(L -glutamate)- b -poly(2-acryloyloxyethyllactoside)- b -poly(L -glutamate) triblock copolymers

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2004
    Chang-Ming Dong
    Abstract A novel class of biomimetic glycopolymer,polypeptide triblock copolymers [poly(L -glutamate),poly(2-acryloyloxyethyllactoside),poly(L -glutamate)] was synthesized by the sequential atom transfer radical polymerization of a protected lactose-based glycomonomer and the ring-opening polymerization of ,-benzyl- L -glutamate N -carboxyanhydride. Gel permeation chromatography and nuclear magnetic resonance analyses demonstrated that triblock copolymers with defined architectures, controlled molecular weights, and low polydispersities were successfully obtained. Fourier transform infrared spectroscopy of the triblock copolymers revealed that the ,-helix/,-sheet ratio increased with the poly(benzyl- L -glutamate) block length. Furthermore, the water-soluble triblock copolymers self-assembled into lactose-installed polymeric aggregates; this was investigated with the hydrophobic dye solubilization method and ultraviolet,visible analysis. Notably, this kind of aggregate may be useful as an artificial polyvalent ligand in the investigation of carbohydrate,protein recognition and for the design of site-specific drug-delivery systems. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5754,5765, 2004 [source]


    Homologous series of alkylsilylphenyl-substituted poly (p -phenylenevinylene)s for light-emitting diodes

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2004
    Sung-Ho Jin
    Abstract Substituent-induced electroluminescence polymers,poly[2-(2-dimethyldodecylsilylphenyl)-1,4-phenylenevinylene] [(o -R3Si)PhPPV], poly[2-(3-dimethyldodecylsilylphenyl)-1,4-phenylenevinylene] [(m -R3Si)PhPPV], and poly[2-(4-dimethyldodecylsilylphenyl)-1,4-phenylenevinylene] [(p -R3Si)PhPPV],were synthesized according to the Gilch polymerization method. The band gap and spectroscopic data were tuned by the dimethyldodecylsilyl substituent being changed from the ortho position to the para position in the phenyl side group along the polymer backbone. The weight-average molecular weights and polydispersities were 8.0,96 104 and 3.0,3.4, respectively. The maximum photoluminescence wavelengths for (o -R3Si)PhPPV, (m -R3Si)PhPPV, and (p -R3Si)PhPPV appeared around 500,530 nm in the green emission region. Double-layer light-emitting diodes with an indium tin oxide/poly(3,4-ethylenedioxythiophene)/polymer/Al configuration were fabricated with these polymers. The turn-on voltages and the maximum brightness of (o -R3Si)PhPPV, (m -R3Si)PhPPV, and (p -R3Si)PhPPV were 6.5,8.7 V and 1986,5895 cd/m2, respectively. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2347,2355, 2004 [source]


    Polymer,silicate nanocomposites produced by in situ atom transfer radical polymerization

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2004
    Hanying Zhao
    Abstract Polymer,silicate nanocomposites were synthesized with atom transfer radical polymerization (ATRP). An ATRP initiator, consisting of a quaternary ammonium salt moiety and a 2-bromo-2-methyl propionate moiety, was intercalated into the interlayer spacings of the layered silicate. Subsequent ATRP of styrene, methyl methacrylate, or n -butyl acrylate with Cu(I)X/N,N -bis(2-pyridiylmethyl) octadecylamine, Cu(I)X/N,N,N,,N,,N,-pentamethyldiethylenetriamine, or Cu(I)X/1,1,4,7,10,10-hexamethyltriethylenetetramine (X = Br or Cl) catalysts with the initiator-modified silicate afforded homopolymers with predictable molecular weights and low polydispersities, both characteristics of living radical polymerization. The polystyrene nanocomposites contained both intercalated and exfoliated silicate structures, whereas the poly(methyl methacrylate) nanocomposites were significantly exfoliated. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 916,924, 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 polymers

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2003
    Xiaojuan 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, characterization, and antimicrobial activity of some novel poly(ether ketone)s

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2003
    Samir A. Patel
    Abstract Low molecular weight poly(ether ketone)s were synthesized from phenol, 1,4-phenylenedioxy diacetylchloride, chloroacetylchloride, and dichloroalkanes [1,2-dichloroethane and dichloromethane] by a Friedel,Crafts reaction with anhydrous aluminum chloride as a catalyst and carbon disulfide as a solvent. The conditions for the preparation of the poly(ether ketone)s and the chlorine contents obtained with the Carius method were examined, and a reaction scheme for each resin was established. The molecular weights and polydispersities of the resins were obtained by gel permeation chromatography. The polyketones were characterized by IR spectroscopy. The characteristic frequencies due to different functional groups were assigned. The thermal properties of the resins were studied with thermogravimetry and differential scanning calorimetry. The characteristic temperatures of thermal degradation for the poly(ether ketone)s were evaluated with thermogravimetric analysis. The kinetic parameters for the decomposition reactions of the resins were obtained with Broido and Doyle's method, and the heats of fusion were obtained from differential scanning calorimetry thermograms. The polyketones were thermally stable up to 200 C. All the polyketones were tested for their microbial properties against bacteria, fungi, and yeast. The effect of poly(ether ketone)s on the growth of these microorganisms was investigated, and the polyketones were found to inhibit the growth of the microorganisms to a considerable extent. 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2335,2344, 2003 [source]


    Densely grafted polyisocyanides synthesized by two types of polymerization techniques

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2003
    Yanqing Tian
    Abstract A series of novel polyisocyanide- graft -polystyrenes and polyisocyanide- graft -[polystyrene- block -poly(butyl acrylate)]s were synthesized through the grafting-through and grafting-from routes with two types of living polymerization techniques: polymerization with the Pd,Pt ,-ethynediyl dinuclear complex as the initiator and catalyst for the polyisocyanide backbone and atom transfer radical polymerization for the grafted side chain. Through the introduction of a chiral center at the side chain of the polyisocyanide backbone, helical grafted and graft block polyisocyanides were prepared through the grafting-from method. All of the obtained polymers exhibited polydispersities in the range of 1.07,1.41. This might have been the first time grafted polyisocyanides were prepared, especially helical grafted polyisocyanides, through the operation of two living polymerization techniques. 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1871,1880, 2003 [source]


    Synthesis of a novel hybrid liquid-crystalline rod,coil diblock copolymer

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2003
    Yi 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]