Showing papers on "Polymerization published in 1989"

Organic aerogels from the polycondensation of resorcinol with formaldehyde

Abstract: The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer “clusters”. The covalent crosslinking of these “clusters” produces gels which are processed under supercritical conditions to obtain low density, organic aerogels ( ⩽ 0.1 g cm−3). The aerogels are transparent, dark red in colour, and consist of interconnected colloidal-like particles with diameters of approximately 10 nm. The polymerization mechanism, structure and properties of the resorcinol-formaldehyde aerogels are similar to the sol-gel processing of silica.

'Synthetic metals': a novel role for organic polymers

Abstract: Summary form only given. The basic chemistry and physics of polyacetylene, (CH)/sub x/, the prototype conducting polymer which is characteristic of most other conducting polymers, were described together with a description of the polyanilines, a large new class of conducting polymers. Potential technological applications were discussed. Polyacetylene, (CH)/sub x/ is obtained in the form of silvery, flexible films by the polymerization of gaseous acetylene. >

Process and catalyst for producing syndiotactic polyolefins

Abstract: Syndiospecific catalysts and processes for the syndiotactic propagation of a polymer chain derived from an ethylenically unsaturated monomer which contains 3 or more carbon atoms or is a subsituted vinyl compound. The catalysts comprise an unbalanced metallocene cation having sterically dissimilar ring structures joined to a positively charged coordinating transition metal atom and a stable noncoordinating counter anion for the metallocene cation. Both ring structures are substituted cyclopentadienyl rings and one is sterically different from the other. Both are in stereorigid relationship to the coordinating transition metal atom to prevent rotation of the rings by direct stearic hindrence between the ring structures. The catalyst is contacted with a C3+ alpha olefin or other ethylenically unsaturated compound in a polymerization reaction zone and maintained in contact with the catalyst in the reaction zone under polymerization conditions to produce a syndiotactic polymer.

Process for production of a high molecular weight ethylene α-olefin elastomer with a metallocene alumoxane catalyst

Abstract: Disclosed is a process for preparing high molecular weight ethylene-α-olefin elastomers, preferably an ethylene-propylene elastomer, by liquid phase polymerization of the requisite monomers in the presence of a metallocene/alumoxane catalyst system. Preferably, the process is carried out as a slurry polymerization utilizing the metallocene/alumoxane catalyst in supported form on a silica gel support with the α-olefin monomer maintained in liquid state and used in excess to serve as a polymerization diluent. The metallocene component of the catalyst by which the process is practiced is of the formula: ##STR1## wherein M is zirconium, titanium or hafnium; each R 1 independently is a C 1 -C 20 linear, branched or cyclic alkyl group or a C 2 -C 4 cyclic alkylene group which forms a fused ring system group; R 2 is a C 1 -C 6 linear, branched or cyclic alkylene, a Si 1 -Si 2 alkyl substituted silanylene group or an alkyl substituted silaalkylene group; each X independently is an alkyl, aryl, halide, hydride or oxygen bridge of a zirconocene dimer; "y" is a number 2, 3 or 4, and "b" is a number 0 or 1. M is preferably zirconium. Most preferably, the supported zirconocene/alumoxane catalyst is prepolymerized with ethylene or another olefin to provide spherical, free-flowing catalyst particles which give free-flowing particulate elastomer product from the slurry polymerization.

Polymer synthesis and organotransition metal chemistry.

Abstract: Mechanistic and synthetic studies in organometallic chemistry have provided considerable insight into olefin metathesis and Ziegler-Natta polymerization. New homogeneous olefin metathesis catalysts based on high oxidation state transition metals have opened new opportunities in polymer synthesis by providing unprecedented control in ring-opening polymerization of cyclic alkenes. The recent development of living coordinative polymerization systems has led to the preparation of a number of new, interesting materials, including block copolymers, conducting polymers or precursors, and ionophoric polymeric substrates.

Insitu photopolymerization of oriented liquid-crystalline acrylates .3. oriented polymer networks from a mesogenic diacrylate

Abstract: Synthesis, mesomorphism, orientation and photo-initiated chain crosslinking of the liquid-crystalline diacrylate 1,4-phenylene bis{4-[6-(acryloyloxy)hexyloxy]benzoate} (1) are studied. Monomer 1 exhibits a broad nematic phase between 108 and 155°C and a monotropic smectic phase below 88°C. The monomer is uniaxially oriented in its nematic phase at a substrate which has been coated with polyimide and unidirectionally rubbed with tissue. At the transition temperature to the smectic phase the order parameter is measured to be 0,7. During polymerization, the ordering of the mesogens is frozen-in, yielding a uniaxially crosslinked network. The clear films of oriented poly(1) exhibit a birefringence Δn between 0,12 and 0,15, depending on the polymerization temperature. In the highest oriented state of 1 a small reduction of the degree of order is observed during the crosslinking reaction, whereas at higher temperatures and lower ordering of 1, the uniaxially orientation increases upon reaction. A special feature of the oriented networks is that the ordering is maintained while heating at high temperatures. The polymerization of the acrylate groups in the mesomorphic phases proceeds fast and to high conversion. Below 90°C the polymerization behaviour is similar to that of conventional isotropic diacrylates. Above 90°C the polymerization reaction of the liquid-crystalline diacrylate proceeds faster than that of an isotropic diacrylate.

Silicon-based polymer science : a comprehensive resource

Abstract: Introduction: My Favorite Element Organosilicon Chemistry: A Brief Overview Silicon-Containing Polymers Formation of Linear Siloxane Polymers Thermal and Rheological Properties of Alkyl-Substituted Polysiloxanes Pyrid- and 1-Oxypridinyl-Substituted Silanes and Siloxanes New Catalysts for Interfacial Transacylation Reactions Polysiloxane-Based Polymer-Electrolyte Complexes Conformational Analysis of Substituted Polysiloxane Polymers Synthesis and Fractionation Studies of Functionalized Organosiloxanes Novel Poly(imide-siloxane) Polymers and Copolymers Polysiloxane-Thermoplastic Interpenetrating Polymer Networks Non-Gaussian Effects and Intermolecular Correlations in Bimodal Networks of Poly(dimethyisiloxane) New Inorganic-Organic Hybrid Materials Through the Sol-Gel Approach Structure and Growth of Silica Condensation Polymers Hydrolysis and Condensation Kinetics of Dimeric Sol-Gel Species by ^2]9Si NMR Spectroscopy A Silicate Substitution Route to Organosilicon Compounds Organosilicon Polymers for Microlithographic Applications Modifications of Well-Defined Polysilanes Mechanistic Studies of Polysilane Polymerization Polymers and Copolymers of Disilacyclohexadiene: A Non-Alkali-Metal Route to Polysilanes Transition-Metal-Substituted Oligo- and Polysilanes Structures, Phase Transitions, and Morophology of Polysilylenes Order-Disorder Transitions and Thermochromism of Polysilylenes in Solution: Theory and Experiment Configurational Properties of a Stiff-Chain Diaryl-Substituted Polysilane in Dilute Solution Radiation Sensitivity of Soluble Polysilane Derivatives Exciton-Exciton Annihilation in Polysilanes Electronic Transport in Polysilylenes Synthesis and Properties of Silicon-Branched Organosilicon Polymers Electronic Structures of Silicon-Based Polymers Band Structure and Optical Absorption Properties of Polysilane Chains Ground States and Ionization Energies of Polysilane Oligomers Synthesis of Some Organosilicon Polymers and Their Pyrolytic Conversion to Ceramics Polymeric Routes to Silicon Carbide and Silicon Nitride Fibers New Polymer Precursors for Silicon Nitride Oxidation Reaction of Polycarbosilane Synthesis and Properties of Silicon-Containing Polyacetylenes Brominated Poly(1-trimethylsilyl-1-propyne): Lithography and Photochemistry Stereoregular Anionic Ring-Opening Polymerization of Silacyclopent-3-enes Stereoregular 1,4 Polymerization of 2-Triethylsilyl-1,3-butadiene Synthesis and Lithographic Evaluation of a Poly(acylsilane) Siloxane Surface Activity Synthesis, Properties, and Potential Applications of Silphenylene-Siloxane Polymers Future Directions for Silicon-Based Polymers

Structural analysis of poly(3‐alkylthiophene)s

Abstract: Poly(3-hexylthiophene) (PT6), poly(3-octylthiophene) (PT8), poly(3-decylthiophene) (PT10) and poly(3-dodecylthiophene) (PT12) were synthesized by electrochemical and chemical polymerization. Investigation of these polymers by means of gel permeation chromatography indicates that the polymers prepared from the different monomers under similar conditions do not differ substantially considering molecular weight and molecular weight distribution. Bimodal distributions were found for electropolymerized polymers, and with increasing polymerization time, the high-molecular-weight and probably highly branched fraction increased relatively to the low-molecular-weight fraction. The microstructure of the polymers was investigated by nuclear magnetic resonance, and it has been found that the polymers exhibit more types of structural units than expected from a simple coupling of adjacent thiophene moieties in 2,5′-positions. Chemical oxidation with iron trichloride in chloroform gave soluble, high-molecular-weight poly(3-alkyl-thiophene)s with a rather low amount of irregular couplings, and these more regular polymers exhibited a higher degree of crytallinity. Room temperature conductivities of the oxidized polymers were between 0,1 and 30 S/cm depending on the polymerization conditions, but these values were rather independent of the length of the alkyl substituent.

Method of forming shaped hydrogel articles including contact lenses

Abstract: Shaped hydrogel articles such as soft contact lenses are prepared by (1) molding or casting a polymerization mixture comprising: (a) a monomer mixture comprising a major proportion of a hydrophilic (meth)acrylate ester such as 2-hydroxyethyl methacrylate, and a cross-linking monomer; and (b) a water-displaceable diluent, wherein said diluent has a viscosity of at least 100 MPa Sec at 30°C, and wherein said diluent consists essentially of a boric acid ester of certain dihydric alcohols, said dihydric alcohols having Hansen polar (.delta.p) and Hansen hydrogen bonding (.delta.h) cohesion parameters falling within the area of a circle defined as having a center at .delta.h = 20.5, .delta.p = 13, and a radius of 8.5, to produce a shaped gel of a copolymer of said monomers and said diluent, and (2) thereafter replacing said diluent with water.

Polythiophenes, process for their preparation and their use

Abstract: The invention relates to new polythiophenes containing structural units of the formula ##STR1## in which A denotes an optionally substituted C 1 -C 4 -alkylene radical, their preparation by oxidative polymerization of the corresponding thiophenes and the use of the polythiophenes for imparting antistatic properties on substrates which only conduct electrical current poorly or not at all, in particular on plastic mouldings, and as electrode material for rechargeable batteries

Nonlinear optical effects in organic polymers

Abstract: Theory of Nonlinear Polarizability in Organic Low Dimensional Systems.- Impact of Dimensionality in the Optical Nonlinearities.- Theoretical Design of Organic Molecules and Polymers for Optoelectronics.- Structural Relaxation and Nonlinear Zero-Point Fluctuations as the Origin of the Anisotropic Third-Order Nonlinear Optical Susceptibility in Trans-(CH)x.- Nonlinear Susceptibility of Organic Systems.- Third-Order Nonlinear Susceptibility in Semiconducting Polymers.- Recent Nonlinear Optical Studies of MNA and Conjugated Linear Chains.- Quadratic Nonlinear Behaviour of Various Langmuir-Blodgett Molecules.- Prediction of Third Order Nonlinear Optical Activity in Ordered Polymers.- Effect of ?-Electron Delocalization on the Second-Order Polarizability of Disubstituted Hydrocarbons.- Synthesis and Nonlinear Optical Properties Characterization of New 1-D Conjugated Polymers.- Studies of Structure-Property Relations.- Synthesis of new Nonlinear Optical Ladder Polymers.- Nonlinear Optical Properties of poly(p-Phenylene Vinylene) thin Films.- The Synthesis and Properties of some Novel Diacetylene Monomers and Polymers.- Design and Optical Properties of a low Energy gap Conjugated Polymer: Polydithieno (3,4-b:3',4'-d)Thiophene.- Synthetic Approaches to Stable and Efficient Polymeric Frequency Doubling Materials. Second-Order Nonlinear Optical Properties of Poled, Chromophore-Functionalized Glassy Polymers.- Langmuir-Blodgett Films of Rigid rod Polymers with Controlled Lateral Orientation.- Polymers and Molecular Assemblies for Second-Order Nonlinear Optics.- Spectral Properties and Second-Harmonic Generation of Hemicyanine dye in Langmuir-Blodgett Films.- Experimental Methods.- Cubic Susceptibility of Organic Molecules in Solution.- Measurement of the Non-Linear Refractive Index of some Metallocenes by the Optical Power Limiter Technique.- Polymerization and X-ray Structure of new Symmetrical and Unsymmetrical Diacetylenes.- Application of Organic Polymers in NLO Devices.- Third-Order Nonlinear Guided-Wave Devices.- Organic Integrated Optical Devices.- Orientationally Ordered Nonlinear Optical Polymer Films.- Overview-Nonlinear Optical Organics and Devices.- Non Linear Optical Polymers for Active Optical Devices.- Linear Electrooptic Coefficient of a Ferroelectric Polymer.- Application of Third-Order Non-Linearities of Dyed PVA to Real-Time Holography.- Device Applications and Materials Requirements.- Ultrafast Third-Order Non-linear Optical Processes in Polymeric Films.- Picosecond Phase Conjugation in Yellow Polydiacetylene Solutions.- Picosecond Studies of Optical Stark Effect in Polydiacetylenes.- Four Working Groups Reports.- Ultrafast Phenomena in Conjugated Polymers.- Device Applications and Materials Requirements.- Polymer Synthesis for Nonlinear Optics and Characterization.- Characterization Techniques.

Insitu photopolymerization of an oriented liquid-crystalline acrylate .2.

Abstract: The photoinitiated polymerization of 4-biphenylyl 4-(6-acryloyloxyhexyloxy)benzoate (1) in its oriented liquid-crystalline state was studied. Monomer 1 has a thermotropic nematic phase between 88°C and 98°C, a monotropic nematic phase between 76°C and 88°C, and a monotropic smectic phase below 76°C. The orientation of 1 was established in a glass cell provided with a rubber polyimide coating and characterized by birefringence measurements. During polymerization both the birefringence and the liquid-crystalline transition temperatures increase, indicating that the orientation was maintained. The oriented poly(1) is polycrystalline at room temperature, becomes smectic at 90°C, nematic at 172°C, and isotropic at 190°C. The order parameter of the nematic poly(1) is lower than that of the nematic monomer1 at equal reduced temperatures.

Water-absorbent resin and production process

Abstract: Water-absorbent resins having an average particle diameter of 100 to 600 μm and a particle diameter distribution of 0.35 or less are prepared by polymerizing an aqueous solution of a water-soluble ethylenically unsaturated monomer, pulverizing and sieving the gel-like polymer so obtained, and crosslinking the surface of the polymer powder. In an alternative process, an aqueous solution of the monomer having a viscosity greater than 15 cps is dispersed in a hydrophobic organic solvent and polymerized to obtain a polymer powder, and the surface of the polymer powder is crosslinked.

Increased Wall-to-Wall Curing Contraction in Thin Bonded Resin Layers

Abstract: Wall-to-wall (WTW) polymerization contraction of filled and unfilled chemically and photo-initiated resins was studied in relation to the WTW distance. In an experimental set-up, the resins were bonded to two opposing disks, and the axial (WTW) displacement resulting from the polymerization shrinkage was measured continuously. It was found that the WTW contraction increased with decreasing WTW distance and ultimately reached a value of almost three times the linear polymerization shrinkage.

Monomer-addition growth with a slow initiation step: A growth model for silica particles from alkoxides

Abstract: A simplified monomer-addition model with a first-order activation step is developed to describe the dynamics of growth of silica particles from alkoxides. In the fimit of slow hydrolysis, we obtain expressions for the evolution of the particle mass and particle polydispersity, as well as an expression for the particle size as a function of the hydrolysis rate constant, the polymerization rate constant, and the initial concentration of the orthosilicate. We find that the formation of the particles is adequately modeled by a reaction limited growth. © 1989 Academic Press, Inc.

Olefin polymerization catalyst component, olefin polymerization catalyst and process for the polymerization of olefins

Abstract: In accordance with the present invention, there are provided olefin polymerization catalyst components comprising an organoaluminum oxy-compound having less than 10% in terms of Al atom of Al component dissolving in benzene kept at 60° C., and olefin polymerization catalyst containing said olefin polymerization catalyst components. The olefin polymerization catalysts have excellent polymerization activities, and are capable of giving olefin (co)polymers having a narrow molecular weight distribution and a narrow composition distribution.

The degrees of polymerization and N-acetylation of chitosan determine its ability to elicit callose formation in suspension cells and protoplasts of Catharanthus roseus.

Abstract: Partially and fully deacetylated chitosan fragments and oligomers were compared for their potency to elicit formation of the 1.3-β-glucan callose in suspension-cultured cells and protoplasts of Catharanthus roseus (line 385). Chitosan oligomers induced little callose formation, while callose synthesis increased with the degree of polymerization of chitosan up to several thousand corresponding to a molecular mass near 106 Da. At a comparable degree of polymerization, partially N-acetylated chitosan fragments were less effective. Colloidal chitin and chitin oligomers induced only trace callose synthesis in protoplasts. These results indicate that the primary interaction involved the amino groups of chitosan and numerous negative charges at the surface of the plasma membrane with spacing in the nanometer range and occurring regularly over micrometer stretches. Charged phospholipid head-groups may fulfill these requirements. The resulting alteration of membrane fluidity may lead to the changes in ion transport known to be associated with the induction of callose formation.

Water sorption and solubility of resin-based materials following inadequate polymerization by a visible-light curing system.

Abstract: The water sorption and solubility of three hybrid and one microfine composite are reported. The values obtained are dependent on composite type and resin system. Incomplete polymerization of the two materials resulted in increased solubility and sorption due to incomplete conversion of the monomer. The marked increased in both parameters will have clinical significance on the durability of the material.

A study of the mechanism of aniline polymerization

Abstract: A chemical polymerization of aniline is quenched at specific reaction time intervals and the amounts of unreacted aniline and formed p-aminodiphenylamine is observed. Oxidation of aniline to generate p-aminodiphenylamine is observed. Oxidation of aniline to generate p-aminodiphenylamine is the slow step in the plymerization. Furthermore, the tetramer of aniline is used as starting material for polymerization under the same conditions as polymerization of aniline. Direct coupling of two tetramers leading to polymer is not observed. A mechanism of polymerization of aniline is proposed

Insitu photopolymerization of oriented liquid-crystalline acrylates .4. influence of a lateral methyl substituent on monomer and oriented polymer network properties of a mesogenic diacrylate

Abstract: Mesomorphism and the molecular orientation of 1,4-phenylene bis{4-(6-(acryloyloxy)hexyloxy)benzoate} (1) and its derivative with a methyl-substituent in the central phenylene group (2) are studied. The methyl group affects the transition temperatures and the thermodynamic parameters, but not the order parameter of the monomers. The photoinitiated polymerization of the diacrylate monomers in their uniaxially oriented state leads to highly oriented and densely crosslinked polymer networks. The order parameter of these networks depends on the polymerization temperature, but becomes nearly temperature-independent after polymerization. The presence of the methyl group leads to a significant lower degree of order in the polymeric state. In addition, data are presented on the monomeric viscosity of 2 and on the tensile moduli, glass transitions and refractive indices of the oriented polymer networks. In order to extend the mesomorphous temperature range, mixtures of 1 and 2 are also investigated.

Modeling of network formation in free radical polymerization

Abstract: Proposition de modeles cinetiques de formation de reseau dans la polymerisation radicalaire pour les periodes de pre- et de post-gelification, modeles bases sur la methode de la constante de vitesse pseudocinetique et pouvant rendre compte de reactions de cyclisation primaire et secondaire

Comprehensive polymer science : the synthesis, characterization, reactions & applications of polymers

Abstract: Catalysis, Mechanisms, and Kinetics of Polymerization. Reactivity in radical copolymerization. Synthesis of Polymers and Novel Structures. Synthesis and properties of dendrimers and hyperbranched polymers. Advanced Polymer Characterization Methods. Recent advances in optical microscopy and its application to the characterization of polymers (M. Srinivasarao). Crystallization and Other Phase Transitions. Theories of polymer crystallization: status and future outlook. Structure-Property Relationships in Selected Classes of Polymers. Structure-property relationships in perfluoropolyethers: a family of polymeric oils. Theories of Rubber Elasticity. Recent developments in the molecular theory of rubber elasticity. Special Topics of Current Interest. Statistical thermodynamics of copolymers and their blends.

Novel anionic polymerization of masked disilenes to polysilylene high polymers and block copolymers

Abstract: Polysilylenes, the linear silicon-silicon bonded polymers, have several interesting properties and are a subject of current intense investigations. Polysilylenes are prepared mostly by the Wurtz-type coupling reactions of dichlorodialkylsilanes which, however, have several difficulties such as the poor control of structure, molecular weight, and polydispersity. The yields of polymers are also usually low. In this paper, we will describe an entirely novel method of preparing polysilylenes based on anionic polymerization of masked disilenes.

Copolymerization of cycloalkenes with ethylene in presence of chiral zirconocene catalysts

Abstract: The chiral catalyst ethylene(bisindenyl)zirconiumdichloride/methylaluminoxane, which is soluble in hydrocarbons, allows the polymerization of cyclic alkenes, e. g. cyclopentene, to form isotactic polymers. No ring opening reaction occurs. To reduce the high melting point of the polycyclopentene, copolymers with ethylene were synthesized. The copolymerization of cyclopentene with ethylene shows similar reaction rates as found for the homopolymerization of ethylene. From 13C NMR spectroscopically calculated rates of incorporation of cyclopentene or cycloheptene in the polymers the copolymerization parameters can be deduced. With increasing polymerization temperature from −10 to 20°C the r1 values rise significantly from 80 to 300. Up to 10 mol-percnt; of cyclopentene monomeric units in the polymer the comonomer is incorporated statistically, whereas a higher content of comonomer leads to two-block formation.

Autoacceleration and kinetics of electrochemical polymerization of aniline

Abstract: A convenient method is presented for determining the rate of polyaniline formation in the electrochemical polymerization of aniline in aqueous HCl solution utilizing cyclic potential sweep techniques. In this method, the mass of polyaniline deposited on a platinum electrode is correlated with the polymer anodic peak current that is recorded during the polymerization. The rates of polymer deposition were therefore monitored by the increases in the anodic peak current at various concentrations of aniline. A kinetic expression obtained for the polymerization accounts well for the autoacceleration process in the electrochemical polymerization of aniline and supports the mechanism of polymerization in which monomeric aniline is incorporated in the growing polymer.