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Polymer Structures (polymer + structure)
Selected AbstractsUV Laser-Induced Gas-Phase Copolymerization of Carbon Disulfide and EtheneMACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2004Radmila Tomovska Abstract Summary: The laser irradiation at 193 nm of a gaseous mixture of carbon disulfide and ethene induces the copolymerization of both compounds and affords the chemical vapour deposition of a C/S/H polymer, the composition of which indicates the reaction between two to three CS2 molecules and one C2H4 molecule. Polymer structure is interpreted on the basis of X-ray photoelectron and FT-IR spectra as consisting of >CS, >CC<, CH2CH2, (CC)SnC4,,,n, C(CS)S, S(CS)S, and CSSC configurations. The gas-phase copolymerization of carbon disulfide and ethene represents the first example of such a reaction between carbon disulfide and a common monomer. Scheme showing the expected reaction of excited CS2 molecules with other CS2 molecules to form dimers, which then react with another CS2 molecule or add to ethene. [source] Properties of amylopectin/montmorillonite composite films containing a coupling agentJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007D. Nordqvist Abstract The addition of clay to polymers has the combined effects of enhancing both the strength/stiffness and the barrier properties. This investigation presents a novel approach to further enhance the strength/stiffness of cast plasticized amylopectin (AP)/Na+ -montmorillonite clay films using a water-soluble coupling agent, poly[(isobutylene- alt -maleic acid, ammonium salt)- co -(isobutylene- alt -maleic anhydride)], between the filler and the matrix. The addition of clay increased the strength and stiffness of the film and the addition of 0.4 parts of a coupling agent per 1 part clay further increased these properties. The trends were the same after each treatment, and there were always significant differences in stiffness and strength between the films without clay and with clay with 0.4 parts of the coupling agent. The increase in stiffness/strength in the presence of a small amount of the coupling agent suggested that it had a bridging effect, presumably through strong secondary bonds to the clay and to the matrix. Infrared spectroscopy and moisture swelling experiments indicated that ester bonds were formed between the coupling agent and AP. X-ray spectroscopy and transmission electron microscopy revealed that the clay-particle/polymer structure was qualitatively independent of the presence of the coupling agent showing a mixture of intercalated clay stacks and exfoliated platelets. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4160,4167, 2007 [source] Chemical Reactivity of Polypyrrole and Its Relevance to Polypyrrole Based Electrochemical SensorsELECTROANALYSIS, Issue 16 2006Krzysztof MaksymiukArticle first published online: 26 JUL 200 Abstract One of the most frequently used conducting polymers, polypyrrole, can take part in chemical processes with typical components of ambient media: oxygen, acids, bases, redox reactants, water, and organic vapors; it can also incorporate nonreactive ions and surfactants from solutions. The influence of such processes on changes of the polymer structure, composition and on possible degradation is analyzed. The benefits and disadvantages of such processes for analytical characteristic of polypyrrole based electrochemical sensors are considered. This discussion is focused on potentiometric ion sensors, where polypyrrole is either a receptor membrane or an ion-to-electron transducer placed between a solid state electrode support and a typical ion-selective membrane. [source] Magnetically Controllable Silver Nanocomposite with Multifunctional Phosphotriazine Matrix and High Antimicrobial ActivityADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Panagiotis Dallas Abstract A recently developed multi-functional phosphotriazine-based polymer is used as a matrix for embedding ,-Fe2O3 nanoparticles as well as a suitable chemical template for surface modification with silver nanoparticles. For the primary magnetic modification, maghemite nanoparticles are surface modified with oleic acid in order to render them organophilic and to prevent the aggregation of the nanoparticles. This aggregation could occur as the polymer synthesis, based on reaction of phosphonitrilic chlorine and 1,4-phenylenediamine, takes place in toluene. The surface active amine units of the polymer structure enable the reduction of silver cations to silver nanoparticles, which are well attached and finely dispersed on its surface. The developed nanocomposite represents one of the few magnetically controllable antibacterial agents based on silver nanoparticles. Magnetic measurements reveal the completely suppressed interactions among maghemite nanoparticles because of their perfect surface coating with an organic surfactant and fine dispersion inside the polymer matrix. This magnetic nanocomposite exhibits a high antibacterial and antifungal activity as proven by tests with nine bacterial strains and four candida (yeast genus) species. For the majority of the tested species, the minimum-inhibition concentrations are below 100,mg,L,1, which is comparable to their equivalent minimum-inhibition concentrations in colloidal silver systems. [source] Porous Polymer Coatings: a Versatile Approach to Superhydrophobic SurfacesADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Pavel A. Levkin Abstract Here, a facile and inexpensive approach to superhydrophobic polymer coatings is presented. The method involves the in situ polymerization of common monomers in the presence of a porogenic solvent to afford superhydrophobic surfaces with the desired combination of micro- and nanoscale roughness. The method is applicable to a variety of substrates and is not limited to small areas or flat surfaces. The polymerized material can be ground into a superhydrophobic powder, which, once applied to a surface, renders it superhydrophobic. The morphology of the porous polymer structure can be efficiently controlled by composition of the polymerization mixture, while surface chemistry can be adjusted by photografting. Morphology control is used to reduce the globule size of the porous architecture from micro down to nanoscale thereby affording a transparent material. The influence of both surface chemistry as well as the length scale of surface roughness on the superhydrophobicity is discussed. [source] Biodegradable polymers: An updateISRAEL JOURNAL OF CHEMISTRY, Issue 4 2005Ariella Shikanov The use of polymeric materials for the administration of pharmaceuticals, and as biomedical devices has increased dramatically. This review focuses on synthetic biodegradable polymers of current interest for medical use, based on ester and anhydride bonds. Special attention is given to factors affecting biodegradation, including: polymer structure, morphology, molecular weight, radiation, and chemical treatment, as well as the effects of drugs and plasticizers added to the polymer mass. The toxicity and biocompatibility of the polymers and their current and future applications in medicine are also briefly reviewed. [source] Preparation and properties of heat-shrinkable cross-linked low-density polyethyleneADVANCES IN POLYMER TECHNOLOGY, Issue 2 2003J. Morshedian Abstract In this work, heat-shrinkable characteristics of a polyethylene compound were obtained by blending mixtures of low-density polyethylene with varying amount of peroxide. These were then extruded and molded to the required shape and then cross-linked by chemical means, followed by heating and stretching and then cooled to "freeze-in" the oriented polymer structure (elastic memory). A decrease in the melting point and heat of fusion (,Hf), as determined from the DSC melting enthalpies, was observed with an increase in the dicumyl peroxide (DCP) concentration. Tests on the heat shrinkablity of the samples showed that the stretching temperature has a large effect on the shrinkage temperature. The results showed that by increasing the peroxide content, the shrinkage temperature was decreased. The elongation at break decreased with an increase in the DCP concentration. Increasing the temperature in lightly cross-linked samples (low percent DCP) resulted in a reduction in the elongation at break. Increasing the cross-linking density (DCP content) gave an opposite effect. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 112,119, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10041 [source] Synthesis, light emission, and photovoltaic properties of perylene-containing polyacetylenesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2008Jianli Hua Abstract Perylene (Py)-containing polyacetylenes with different skeleton structures [HCC(C6H4)CO2Py]n (P1), [HCC(CH2)8CO2Py]n (P2), and {[(C6H5) CC(CH2)9NH2]co[(C6H5)CC(CH2)9Py]}n (P3) are synthesized in satisfactory yields by Rh-catalyzed polymerization (for P1 and P2) and polymer reaction (for P3). All the polymers are soluble and possess high molecular weights (Mw up to 2.8 × 105). Their structures and properties are characterized and evaluated by IR, NMR, UV, TGA, PL, and photovoltaic (PV) analyses. The polymers are thermally stable, losing little of their weights when heated to 330 °C. When their solutions are irradiated, their perylene pendants emit intense red fluorescence at 610 nm. PV cells with a configuration of ITO/PEDOT:PSS/polymer/LiF/Al are fabricated, which show maximum current density of 10.3 ,A/cm2. The external quantum efficiency is sensitive to the polymer structure, with P3 exhibiting the highest value of 0.23%. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2025,2037, 2008 [source] Synthesis and properties of an ionic polyacetylene with aromatic heterocyclesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007Yeong-Soon Gal Abstract A new ionic polyacetylene with two aromatic heterocycles (pyridyl and thienyl) was prepared by the activation polymerization of 2-ethynylpyridine by using 3-(6-bromohexyloxy)methylthiophene without any additional initiator or catalyst. The activated acetylenic triple bond of N -substituted-2-ethynylpyridinium bromide, formed at first quaternarization process, was susceptible to linear polymerization. The instrumental analysis data on the polymer structure revealed that the polymer have the conjugated polyene backbone structure with the designed two aromatic heterocycles. The photoluminescence peak is located at 510 nm corresponding to a photon energy of 2.43eV. The electrochemical properties of this ionic polyacetylene were also measured and discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5679,5685, 2007 [source] Synthesis and characterization of poly(ethylene oxide- co -ethylene carbonate) macromonomers and their use in the preparation of crosslinked polymer electrolytesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2006Anette Munch Elmér Abstract Methacrylate-functionalized poly(ethylene oxide- co -ethylene carbonate) macromonomers were prepared in two steps by the anionic ring-opening polymerization of ethylene carbonate at 180 °C, with potassium methoxide as the initiator, followed by the reaction of the terminal hydroxyl groups of the polymers with methacryloyl chloride. The molecular weight of the polymer went through a maximum after approximately 45 min of polymerization, and the content of ethylene carbonate units in the polymer decreased with the reaction time. A polymer having a number-average molecular weight of 2650 g mol,1 and an ethylene carbonate content of 28 mol % was selected and used to prepare a macromonomer, which was subsequently polymerized by UV irradiation in the presence of different concentrations of lithium bis(trifluoromethanesulfonyl)imide salt. The resulting self-supportive crosslinked polymer electrolyte membranes reached ionic conductivities of 6.3 × 10,6 S cm,1 at 20 °C. The coordination of the lithium ions by both the ether and carbonate oxygens in the polymer structure was indicated by Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2195,2205, 2006 [source] Using polymers to control substrate, ligand, or catalyst solubilityJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2001David E. Bergbreiter Abstract The attributes and design of soluble polymer supports for catalysis and synthesis are discussed. By manipulating polymer structure, polymer supports can be prepared so that the solubility of an attached reagent, substrate, or ligand is affected by heating, cooling, pH, or solvent identity. Supports with such engineered solubility are useful both in organic synthesis and catalysis. They can be used as purification handles in organic synthesis as a way to recover catalysts, as a way to turn reactions on or off, and more generally, as a handle for separations. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2351,2363, 2001 [source] The tenth anniversary of Suzuki polycondensation (SPC)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2001A. D. Schlüter Abstract This article describes the successful transfer of the Suzuki cross-coupling (SCC) reaction to polymer synthesis, one of the major developments within the last decade of polymer synthesis. The polymers prepared by Suzuki polycondensation (SPC) and its Ni-catalyzed reductive counterpart are soluble and processable poly(arylene)s that, because of their rigid and conjugated backbones, are of interest for the materials sciences. Achievable molar masses easily compete with those of traditional polyesters and polyamides. This article also provides insight into some synthetic problems associated with the transfer of SCC from low molar mass organic chemistry to high molar mass polymer chemistry by addressing issues such as monomer purity, stoichiometric balance, achievable molar masses, and defects in the polymer structure. Although the emphasis of this article is synthetic and structural issues, some potential applications of the polyarylenes obtained are briefly mentioned. Together with the enormous developments in the areas of metallocene, ring-opening metathesis, and acyclic diene metathesis polymerization, the success of SPC impressingly underlines the increasing importance of transition-metal-catalyzed CC-bond-forming reactions in polymer synthesis. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1533,1556, 2001 [source] Polymer plasticization using supercritical carbon dioxide,JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2008Febe Kusmanto The plasticizing effect of supercritical CO2 (scCO2) during the extrusion of polymers was investigated. A modified extrusion system was used to demonstrate the viscosity-reducing effect of scCO2 together with a capability to produce foam-free extrudate with selected polymers, including poly(vinyl chloride). Samples of extrudate and materials prepared off-line by using a pressure vessel were characterized by thermal, mechanical, and X-ray techniques. After gas diffusion from the polymer, there was no long-term effect on polymer structure and properties. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers. [source] Luminescence properties of poly- (phenylene vinylene) derivativesPOLYMER INTERNATIONAL, Issue 3 2008Cuong Ton-That Abstract BACKGROUND: Conjugated polymers, especially those of the poly(phenylene vinylene) (PPV) family, are promising candidates as emission material in light-emitting devices. The aim of this work was to investigate the dependence of the luminescence properties of PPV-based derivatives on their polymer structure, especially side groups. RESULTS: Three PPV derivatives, BEHPPV, MEHPPV and MEHSPPV, were synthesised and characterised by photoluminescence (PL) and cathodoluminescence (CL) spectroscopies in the temperature range 10,300 K. PL and CL spectra of the polymers exhibit similar luminescence peaks, which undergo a blue shift with increasing temperature. The shift in wavelength is accompanied by variations in the relative intensities of emission peaks. Both BEHPPV and MEHPPV display emission characteristics of the PPV backbone, but the peak of MEHPPV shifts to a longer wavelength in comparison with the corresponding peak of BEHPPV at the same temperature. The luminescence spectra of MEHSPPV, which has a sulfanyl incorporated in the side chain, are considerably different from those of the two other derivatives. CONCLUSIONS: The results demonstrate that the luminescence properties depend strongly on the chain conformations of the conjugated backbone, which are affected by polymer side chains. Copyright © 2007 Society of Chemical Industry [source] Electrospray mass spectrometry studies of macromolecules containing 1,3-oxazolidine moietiesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004J. Ma, ska-Solich The polycondensation of terephthalaldehyde with 2-amino-2-methyl-1,3-propanediol using acidic catalysts leads to the formation of linear polymers and macrocyclic compounds with 2-(1,,4,-phenylene)-5-methyl-1-aza-3,7-dioxabicyclo[3.3.0]octane as the repeating unit in all compounds. The structure of the polymer was determined by 1H- and 13C-NMR spectroscopy, and electrospray ionization mass spectrometric (ESI-MS) analysis. ESI-MS measurements were used to study the details of the polymer structure and support the equimolar alternating nature of bicyclo- O,N -acetals of terephthaldehyde in these macromolecules. Copyright © 2004 John Wiley & Sons, Ltd. [source] catena -Poly[[dinitratocadmium(II)]bis[,-bis(2-methyl-1H -imidazol-1-yl)methane-,2N3:N3,]]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2007Chuan-Ming Jin The title compound, [Cd(NO3)2(C9H12N4)2]n, has a one-dimensional double-bridged chain polymer structure with a 16-membered macrometallacyclic tetragonal structural motif. The CdII ion occupies a crystallographic inversion centre and is coordinated by four equatorial N atoms from four distinct bis(2-methylimidazol-1-yl)methane ligands and two apical nitrate O atoms to form a slightly distorted octahedral coordination geometry. [source] CO2 and SnII Adducts of N-Heterocyclic Carbenes as Delayed-Action Catalysts for Polyurethane SynthesisCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2009Bhasker Bantu Abstract Catalytic rivals: Both CO2 -protected tetrahydropyrimidin-2-ylidene-based N-heterocyclic carbenes (NHCs) and SnII -1,3-dimesitylimidazol-2-ylidene, as well as SnII -1,3-dimesitylimidazolin-2-ylidene complexes (example displayed), have been identified as truly latent catalysts for polyurethane (PUR) synthesis rivaling all existing systems both in activity and latency. A series of CO2 -protected pyrimidin-2-ylidenes as well as 1,3-dimesitylimidazol-2-ylidene and dimesitylimidazolin-2-ylidene complexes of SnII have been prepared. Selected single-crystal X-ray structures are reported. The new compounds were investigated for their catalytic behavior in polyurethane (PUR) synthesis. All compounds investigated showed excellent catalytic activity, rivaling the industrially most relevant catalyst dibutyltin dilaurate. Even more important, all compounds displayed pronounced latent behavior, in selected cases rivaling and exceeding the industrially relevant latent catalyst phenylmercury neodecanoate both in terms of latency and catalytic activity. This allows for creating one-component PUR systems with improved pot lifetimes. Pseudo-second-order kinetics were found for both CO2 -protected tetrahyropyrimidin-2-ylidenes and for [SnCl2(1,3-dimesityldihydroimidazol-2-ylidene)], indicating a fast pre-catalyst decomposition prior to polyurethane formation. 1,3-Di(2-propyl)tetrahydropyrimidin-2-ylidene was additionally found to be active in the cyclotrimerization of various isocyanates, offering access to a broad variability in polymer structure, that is, creating both urethane and isocyanurate moieties within the same polymer. [source] Synthetic Strategies for Controlling the Morphology of Proton Conducting Polymer Membranes,,FUEL CELLS, Issue 2 2005Y. Yang Abstract The nanostructure and morphology of proton conducting polymers is of considerable interest in the search for next generation materials and optimization of existing ones. Synthetic methodologies for tailoring molecular structures that promote nanoscopic phase separation of ionic and non-ionic domains, and the effect of phase separation on parameters such as proton conductivity, are considered. Rather than distinguish proton conducting polymers according to chemical class, they are categorized under sub-headings of random, block, and graft copolymers. The synthetic methodology available to access archetypal polymer structures is dependent on the nature of the monomers and restrictive compared to conventional non-ionic polymer systems. Irrespective of the methodology, ionic aggregation and phase separation are consistently found to play an important role in the proton conductivity of low ion exchange capacity,(IEC) membranes, but less of a role in high IEC membranes. Significant research is required to further develop relationships between polymer architecture, morphology, and electrolytic properties. [source] Synthesis and characterization of diphenylmethyltin(IV) mono-, di-, and trichloroacetateHETEROATOM CHEMISTRY, Issue 1 2003Mostafa Mohammadpour Amini Diphenylmethyltin(IV) mono-, di-, and trichloroacetate have been synthesized and characterized by infrared, 1H, 13C, 119Sn NMR, and mass spectroscopy. Infrared spectroscopy indicates that the prepared organotin carboxylates possess chain polymer structures. NMR data show that the mono- and dichloro derivatives do not retain the solid state structure in solution. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:18,22, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10059 [source] Nanostructured Organic,Inorganic Composite Materials by Twin Polymerization of Hybrid MonomersADVANCED MATERIALS, Issue 20 2009Stefan Spange Abstract Forming two structurally different but associated polymer structures in a single step is a possible route for the production of nanostructured materials. By means of twin polymerization of specially constructed monomers consisting of two different covalently bonded building blocks (hybrid monomers), this route is realized. What is important is that two different macromolecular structures are formed from one monomer in a single process. The two polymers formed can be linear, branched, or cross-linked structures. The molecular composition of the hybrid monomer defines the degree of cross-linking of the corresponding macromolecular structures that is theoretically possible. [source] Effects of hyperbranched poly(amido-amine)s structures on synthesis of Ag particlesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Youyi Sun Abstract The synthesis of Ag particles stabilized poly (N,N,-methylene bisacrylamide N -aminoethyl piperazine) (MBA-AEPZ) and poly(N,N,-dodecyl diacrylamide N -aminoethyl piperazine) (MDA-AEPZ) was reported. The effects of hyperbranched polymer structures and hyperbranched polymer concentrations were studied on the size and size distribution of Ag particles, which were determined from the UV plasmon absorption band and transmission electronmicroscopic analyses. The data show that slight change (10.3 and 9.7 nm) and large change on particle size (3.9 and , 200 nm) were observed with increase in concentrations of poly(MBA-AEPZ) and poly(MDA-AEPZ) at the same M:D, respectively. The difference is explained in terms of a mechanism of structure-dependent stabilization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Release mechanisms from gentamicin loaded poly(lactic- co -glycolic acid) (PLGA) microparticlesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2002Wolfgang Friess Abstract To provide local gentamicin delivery for 1 week based on a biodegradable system, poly(lactic- co -glycolic acid) (PLGA) microparticles were developed utilizing a 50/50 blend of Resomer® RG 502H, an uncapped variety of 13.5 kD, and Resomer® RG 503, an endcapped polymer of 36.2 kD. The liberation mechanism was investigated by analysis of morphological changes and thermal analysis focusing on the polymer glass transition temperature (Tg) and the mechanical properties. The release of gentamicin was related to a structural breakdown of the particles reaching a critical molecular weight. A Tg of <,37°C in the hydrated state was not indicative of collapse and agglomeration of the particles because the mechanical strength of the polymer structures in the rubbery state may still render sufficient support. As the gap between incubation temperature and Tg widened, the mechanical stability of the PLGA microparticles decreased and became decisive. Particles prepared with RG 502H show a lower ability to bear mechanical stress than RG 503 and 50/50 RG 502H/RG 503 microparticles. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91: 845,855, 2002 [source] A paradigm for the mechanisms and products of spontaneous polymerizationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009H. K. Hall Jr. Abstract In spontaneous vinyl and ring-opening copolymerizations, polar and resonance effects on the intermediates from bond-forming initiation offer a continuous spectrum of reactivities and polymer structures. In bond-forming initiation, an electron-rich donor monomer forms a bond to an acceptor monomer. The donor monomer may be a vinyl monomer with O, N, or aryl substituent or it may be an aza- or oxacycle. The acceptor monomer may be a vinyl monomer carrying CN, COOR, or SO2R substituent or it may be a cyclic anhydride or maleimide. Beyond this, the donor may have a ,-like strained single bond, whereas the acceptor may be an electrophilic quinodimethane. Lewis acids may be used to enhance the electrophilicity of acceptor monomers. Reaction rates and polymer composition are determined by systematically varying the stability of the first intermediate, designated P (for polymethylene). The nature of the intermediate will vary from a highly reactive trans biradical, which initiates chain alternating copolymerization, to a cis/gauche zwitterion, which can initiate chain ionic homopolymerization, to an extremely stabilized zwitterion, which cannot add monomer, but builds up in concentration and terminates by combination, forming alternating copolymer. This model embraces the existing literature for a wide variety of monomers and possesses predictive power. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source] The role of mid-chain radicals in acrylate free radical polymerization: Branching and scissionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2008Thomas Junkers Abstract The past 5 years have seen a significant increase in the understanding of the fate of so-called mid-chain radicals (MCR), which are formed during the free radical polymerization of monomers that form highly reactive propagating radicals and contain an easily abstractable hydrogen atom. Among these monomers, acrylates are, beside ethylene, among the most prominent. Typically, a secondary propagating acrylate-type macroradical (SPR) can easily transfer its radical functionality via a six-membered transition state to a position within the polymer chain (in a so-called backbiting reaction), creating a tertiary MCR. Alternatively, the radical function can be transferred intramolecularly to any position within the chain (also forming an MCR) or intermolecularly to another polymer strand. This article aims at providing a comprehensive overview of the up-to-date knowledge about the rates at which MCRs are formed, their secondary reactions as well as the consequences of their occurrence under variable reaction conditions. We explore the latest aspects of their detection (via electron spin resonance spectroscopy) as well as the characterization of the polymer structures to which they lead (via high resolution mass spectrometry). The presence of MCRs leads to the formation of branched polymers and the partial formation of polymer networks. They also limit the measurement of kinetic parameters (such as the SPR propagation rate coefficient) with conventional methods. However, their occurrence can also be used as a synthetic handle, for example, the high-temperature preparation of macromonomers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7585,7605, 2008 [source] Thermolyzable polymer networks and star polymers containing a novel, compact, degradable acylal-based dimethacrylate cross-linker: Synthesis, characterization, and thermolysisJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2007Efrosyni Themistou Abstract A compact, cleavable acylal dimethacrylate cross-linker, 1,1-ethylenediol dimethacrylate (EDDMA), was synthesized from the anhydrous iron(III) chloride-catalyzed reaction between methacrylic anhydride and acetaldehyde. The ability of EDDMA to act as cross-linker was demonstrated by using it for the preparation of one neat cross-linker network, four star polymers of methyl methacrylate (MMA), and four randomly cross-linked MMA polymer networks using group transfer polymerization (GTP). For comparison, the corresponding polymer structures based on the commercially available ethylene glycol dimethacrylate (EGDMA) cross-linker (isomer of EDDMA) were also prepared via GTP. The number of arms of the EDDMA-based star polymers was lower than that of the corresponding EGDMA polymers, whereas the degrees of swelling in tetrahydrofuran of the EDDMA-based MMA networks were higher than those of their EGDMA-based counterparts. Although none of the EDDMA-containing polymers could be cleanly hydrolyzed under basic or acidic conditions, they could be thermolyzed at 200 °C within 1 day giving lower molecular weight products. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5811,5823, 2007 [source] Prediction of Polymer Properties from their Structure by Recursive Neural Networks,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2006Celia Duce Abstract Summary: We propose a new approach for predicting polymer properties from structured molecular representations based on recursive neural networks. To this aim, a structured representation is designed for the modeling of polymer structures. This representation can also account for average macromolecule characteristics. Preliminarily, this model is applied to the calculation of the Tg of (meth)acrylic polymers with different stereoregularity. Representation of poly(methyl methacrylate) as a chemical tree and unfolding of the encoding process through its structure. [source] Template-directed patterning of polymers and biomaterialsMICROSCOPY RESEARCH AND TECHNIQUE, Issue 6 2007Amol Chandekar Abstract A novel method of patterning surfaces with synthetic or biological polymers is demonstrated. It consists of using microcontact printing to pattern a gold surface with an adsorbate that imparts hydrophilicity; the remainder of the surface is covered with one that imparts hydrophobicity. 16-Mercaptohexadecanoic acid (MHDA) and 1H,1H,2H,2H-perfluorodecanethiol, respectively, have been used as the hydrophilic and hydrophobic adsorbates. This functionalized gold surface then serves as a template for patterning hydrophilic polymers and biomaterials, which are either spin-coated or drop-cast onto the surface. Using this methodology, it is shown by atomic force microscopy, scanning electron microscopy (SEM), and fluorescence microscopy that micron-scale patterns of a poly(ethylene)- block -poly(ethylene oxide) copolymer, poly- L -tryptophan, and bovine collagen can be fabricated, with these mimicking the MHDA patterns. For the block copolymer, it is found by atomic force microscopy that the heights of the polymer patterns decrease as their widths decrease. This is believed to be due to the inherent instability of tall, narrow polymer structures and the tendency of the polymer to minimize its exposed surface area. For poly- L -tryptophan, two different molecular weights of this polyamino acid have been studied, and different morphologies within the patterned regions are observed. While oligomeric poly- L -tryptophan (1,000,5,000 g/mol) gives smooth MHDA-covered patterns, the higher molecular weight (15,000,50,000 g/mol) yields fibrous ones. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Synthesis and characterization of a novel soluble reactive ladder-like polysilsesquioxane with side-chain 2-(4-chloromethyl phenyl) ethyl groupsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2001Chunqing Liu Abstract A new kind of soluble structure-ordered ladder-like polysilsesquioxane with reactive side-chain 2-(4-chloromethyl phenyl) ethyl groups (L) was first synthesized by stepwise coupling polymerization. The monomer, 2-(4-chloromethyl phenyl) ethyltrichlorosilane (M), was synthesized successfully by hydrosilylation reaction with dicyclopentadienylplatinum(II) chloride (Cp2PtCl2) catalyst. Monomer and polymer structures were characterized by FT-IR, 1H -NMR, 13C -NMR, 29Si -NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vapor pressure osmometry (VPO) and X-ray diffraction (XRD). This novel reactive ladder-like polymer has promise potential applications as initiator for atom transfer radical polymerization, and as precursor for a variety of advanced functional polymers. Copyright © 2001 John Wiley & Sons, Ltd. [source] Semi-online nanoflow liquid chromatography/matrix-assisted laser desorption ionization mass spectrometry of synthetic polymers using an octadecylsilyl-modified monolithic silica capillary columnRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2010Takehiro Watanabe We have designed a semi-online liquid chromatography/matrix-assisted laser desorption/ionization mass spectrometry (LC/MALDI-MS) system to introduce eluent from a octadecylsilyl (ODS) group modified monolithic silica capillary chromatographic column directly onto a sample plate for MALDI-MS analysis. Our novel semi-online system is useful for rapidly and sensitively examining the performance of a monolithic capillary column. An additional advantage is the small elution volume of a monolithic capillary column, which allows delicate eluents, such as 1,1,1,3,3,3,-hexafluoroisopropyl alcohol (HFIP), to be used to achieve cost-effective analysis. Using the semi-online LC/MALDI-MS system, chromatographic separation of polymers by the monolithic column with different eluents was studied. Separation of poly(methyl methacrylate) and Nylon 6/6 showed that the column functioned via size-exclusion separation when tetrahydrofuran or HFIP eluent was used. On the other hand, the separation behavior of Nylon 11 indicated a reversed-phase mode owing to the interaction of the polymer with the modified ODS group in the column. Using tetrahydrofuran/methanol (1:1, v/v) as the eluent, the LC/MALDI-MS spectra of poly(lactic acid), which contains both linear and cyclic polymer structures, showed that the column could separate the hydrophobic cyclic polymer and elute it out relatively slowly. The monolithic column functions basically via size-exclusion separation; the reversed-phase separation by interaction with the ODS functions may have less influence on column separation. The semi-online monolithic capillary LC/MALDI-MS method we have developed should provide a means of effectively analyzing synthetic polymers. Copyright © 2010 John Wiley & Sons, Ltd. [source] Nickel(II) complexes bearing pyrazolylimine ligand: synthesis, structure, and catalytic properties for vinyl-type polymerization of norborneneAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 4 2010Yuan-yuan Wang Abstract Two nickel(II) complexes of {2-[C3HN2(R1)2 -3,5]}[C(R2)N(C6H3iPr2 -2,6)]NiBr2 (complex 1: R1 = CH3, R2 = 2,4,6-trimethylphenyl; complex 2: R1 = R2 = Ph) were synthesized and characterized. The solid-state structure of complex 1 has been confirmed by X-ray single-crystal analysis. Activated by methylaluminoxane (MAO), complexes 1 and 2 are capable of catalyzing the polymerization of norbornene with moderate activities [up to 10.56 × 105 gPNBE (mol Ni h),1] with high molecular weights (Mw,13.56 × 105 g mol,1) and molecular weight distributions were around 2. The influences of polymerization parameters such as reaction temperature and Al,Ni molar ratio on catalytic activity and molecular weight of the polynorbornene were investigated in detail. The obtained polynorbornenes were characterized by means of 1H-NMR and FTIR techniques. The analytical results of polymer structures indicated that the norbornene polymerization is vinyl-type polymerization rather than ROMP. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||