Showing papers on "Copolymer published in 1990"

Block Copolymer Thermodynamics: Theory and Experiment

Abstract: Block copolymers are macromolecules composed of sequences, or blocks, of chemically distinct repeat units. The development of this field originated with the discovery of termination-free anionic polymerization, which made possible the sequential addition of monomers to various carbanion-ter­ minated ("living") linear polymer chains. Polymerization of just two dis­ tinct monomer types (e.g. styrene and isoprene) leads to a class of materials referred to as AB block copolymers. Within this class, a variety of molec­ ular architectures is possible. For example, the simplest combination, obtained by the two-step anionic polymerization of A and B monomers, is an (A-B) dioblock copolymer. A three-step reaction provides for the preparation of (ABA) or (BAB) triblock copolymer. Alternatively, "living" diblock copolymers can be reacted with an n-functional coupling agent to produce (A-B)n star-block copolymers, where n = 2 constitutes a triblock copolymer. Several representative (A-B)n block copolymer architectures

Novel vinyl carbonate and vinyl carbamate contact lens material monomers

Abstract: Novel monomers of the general formula ##STR1## where b is 0 or 1, a is 1, 2, 3 or 4, R 2 is a monovalent alkyl radical and R is an organic radical. The novel monomers may be employed to produce novel copolymers useful as hydrogel, soft non-hydrogel and/or rigid gas permeable contact lens materials.

Photoinduced phase transition of gels

Abstract: Equilibrium swelling curves of copolymer gels of N-isopropylacrylamide and a photosensitive leucocyanide, were determined as a function of temperature under UV irradiation. Without UV irradiation the gels underwent a sharp continuous volume change, whereas upon UV irradiation they showed a discontinuous volume phase transition. For appropriate temperatures, the gels discontinuously swelled in response to irradiation of light and shrank when the light was removed

The morphology of symmetric diblock copolymers as revealed by neutron reflectivity

Abstract: The specular reflectivity of neutrons has been used to characterize quantitatively the microphase separated morphology of symmetric, diblock copolymers of polystyrene (PS), and polymethylmethacrylate (PMMA), as a function of the total molecular weight of the copolymer where either block is perdeuterated It is shown that the hyperbolic tangent function, as opposed to a linear or cosine‐squared function, most closely describes the concentration gradient at the interface between the lamellar copolymer microdomains The effective width of the interface is found to be independent of the molecular weight of the copolymer blocks and has a value of 50±3 A This interface is also found to be identical to that between PS and PMMA, homopolymers However, using measured values of the Flory–Huggins interaction parameter for PS and PMMA, current theoretical treatments cannot describe the observed widths of the interface

Radiation Curing of Polymeric Materials

Abstract: Photocurable Coatings Electron-Beam Curing of Polymeric Materials Depth of Cure Profiling of UV-Cured Coatings Modified Kubelka-Munk Optical Treatment of Photon Flux in a Coating and Its Relationship to UV Curing as Measured with a UV N101 Cure Tester Time-Resolved Laser Spectroscopy of Synergistic Processes in Photoinitators of Polymerization Photochemistry and Photopolymerization Activity of Water-Soluble Benzophenone Initators Cationic Photoinitiators: Rearrangement Reactions from Direct Irradiation of Diarylhalonium Salts Novel Photoinitiator for Modern Technology Coreactive Photoinitiators from Surface Polymerization Effect of Monomer Structure on Concurrent Grafting During Radiation Curing Photoinitiated Cross-Linking of Polyethylenes and Diene Copolymers Nonacrylate Curing Mechanisms: Photoiniated Cross-Linking Using Amine-Ene Reaction Photoinitiated Cross-Linking of Norbornene Resins with Multifunctional Thiols Acrylated Melamines in UV-Curable Coatings Coatings Curable with Low-Emission Radiation Polymeric Coatings Containing Chlorendic Anhydride: Decomposition Products of Chlorendic Anhydride Photochemical Approaches to Ordered Polymers Comparison of Thermal, Mechanical, and Spectroscopic Techniques for Characterization of Radiation-Cured Adhesives Mechanical Properties of UV-Cured Coatings Containing Multifunctional Acrylates Structure-Performance Relationships of Urethane Acrylates Enthalpy Relaxation in UV-Cured Epoxy Coatings Temperature Effect on the Phase Transformation of UV-Curable Systems Microcolumn Imaging: Simulation of the Microcapsule Imaging System Photolysis Studies of Bisphenol-A-Based Model Compounds: Effect of Decomposition Products on the UV Stability of Bisphenol-A-Based Epoxy Coatings Photooxidative Stability and Photoyellowing of Electron-Beam-and UV-Cured Multifunctional Amine-Terminated Diacrylates Radiation-Induced Cationic Curing of Vinyl-Ether-Functionalized Urethane Oligomers UV Cure of Epoxysiloxanes and Epoxysilicones UV Cure of Epoxy-Silicone Monomers UV-Induced Polymerization of Highly Filled Epoxy Resins in Microelectronics Laser-Initiated Polymerization of Multifunctional Acrylates: Repetition Rate Effects on Percent Conversion UV-Radiation and Laser-Induced Polymerization of Acrylic Monomers High-Energy-Radiation-Induced Cationic Polymerization of Vinyl Ethers in the Presence of Onium Salt Initiators Structure-Property Behavior of Caprolactone-Allyl Glycidyl Ether Copolymers Cross-Linked by Electron-Beam Irradiation Electron-Beam Exposure of Organic Materials: Radiation Curing of Perfluorinated Acrylates Molecular Weight Dependence of E-Beam Resist Sensitivity Electron-Initiated Graft Modification of Polyolefins

Mean-field theory of polymer interfaces in the presence of block copolymers

Abstract: The effects of an A-B diblock copolymer on the properties of an interface between immiscible A and B homopolymers are studied. A complete set of self-consistent field equations is solved numerically in order to determine the profiles of the different polymeric components and the interfacial tension as functions of the degrees of polymerization, the interaction parameter, the statistical segment length and the copolymer chemical potential

A novel micellar synthesis and photophysical characterization of water-soluble acrylamide-styrene block copolymers

Abstract: Block size in the copolymers were determined from Poisson fluorescence quenching kinetics. Fine structure in pyrene probe fluorescence revealed that the blocks impart hydrophobic domains to aqueous copolymer solutions. Fluorescence quenching was monitored to determine that the copolymers isolate and screen hydrophobic molecules from the aqueous phase. A coiled configuration of the polyacrylamide backbone about the styrene blocks in shown to be a contributor to the screening effect

Polymerization of functionalized norbornenes employing Mo(CH-t-Bu)(NAr)(O-t-Bu)2 as the initiator

Abstract: : Norbornenes containing esters, cyano, acetate, and related functionalities can be polymerized in a living manner employing Mo(CH-t-Bu)(NAr) (O-t-Bu)2 as the initiator, especially in THF, to give polymers with polydispersities as low as 1.04. Living polymers containing Mo-alkylidene end groups have been characterized by proton NMR methods.

Stereo block copolymers of L- and D-lactides

Abstract: Sequential diblock copolymers composed of L- and D-lactic acid residues were synthesized through a living ring-opening polymerization of L- and D-lactide initiated by aluminium tris(2-propanolate). The composition of the block copolymers was varied by changing the reaction conditions and monomer over initiator ratio and confirmed by 1H NMR analysis, molecular weight determination and optical rotation measurements. Molecular weights ranged from 1,3 to 2,0 · 104 with 1,2 < Mw/Mn < 1,4. Stereocomplex formation in all block copolymers was determined using differential scanning calorimetry showing melting temperatures of about 205°C.

Rubber‐modified epoxies. I. Influence of carboxyl‐terminated butadiene‐acrylonitrile random copolymers (CTBN) on the polymerization and phase separation processes

Abstract: A bisphenol-A diglycidylether (DGEBA) based epoxy was cured with a cycloaliphatic diamine (4,4′-diamino-3,3′-dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy terminated butadiene-acrylonitrile random copolymer (ETBN). Results showed that vitrification is slightly delayed with the rubber addition. With ETBN the auto-catalytic mechanism by [OH]0 is predominant at the beginning of the reaction, and on the contrary dilution is the dominant factor after x = 0.15. Phase separation takes place completely, well before gelation and vitrification; the conversion at the onset of phase separation decreases with the rubber amount but does not depend significantly on the temperature. The maximum Tg of the rubber-modified matrix does not depend on the cure temperature but decreases with the initial rubber concentration. This implies that a significant amount of rubber remains in solution in the continuous phase. This explains the delay in vitrification.

Process for the preparation of a syndiotactic polyolefin

Abstract: A syndiotactic polyolefin is obtained in a high yield by polymerization or copolymerization of an olefin of the formula R a --CH═CH--R b in the presence of a catalyst consisting of a metallocene of the formula I ##STR1## and an aluminoxane. This polyolefin has a very high syndiotactic index. At a low polymerization temperature, a polyolefin having a low average molecular weight and narrow molecular weight distribution is obtained, and at a high polymerization temperature a polymer having a high average molecular weight and a wide molecular weight distribution is obtained. Shaped articles produced from the polymers are distinguished by a high transparency, flexibility, tear strength and excellent surface gloss.

Expanded articles of biodegradable plastics materials and a method for their production

Abstract: Expanded articles of biodegradable plastics material are produced by the extrusion of a composition including starch, a polymer compatible with starch, in particular, an ethylene-acrylic acid copolymer and/or ethylene-vinyl alcohol copolymer, and an expanding agent. Preferably use is made of sodium bicarbonate as expanding agent in the presence of a polymeric acid.

Molecular weight dependence of lamellar domain spacing of diblock copolymers in bulk

Abstract: Styrene/2-vinylpyridine diblock copolymers are studied by SAXS. It was found that the lamellar domain spacing-molecular weight relationship of the diblock copolymer in bulk is given by D=0.33 7 M 0.64 over the molecular weight range from 38 K to 740 K. The experimental result is in good agreement with the theories on the basis of Gaussian chain statistics in a confined space, particularly the theory of Helfand-Wasserman

Blood compatibility of PEO grafted polyurethane and HEMA/styrene block copolymer surfaces

Abstract: HEMA/styrene (HEMA/STY) block copolymers and poly(ethylene oxide) 4,000 M.W. (PEO4K) grafted Biomer (B-PEO4K) surfaces have been synthesized, characterized, and evaluated as blood-contacting materials. These surfaces have demonstrated improved blood compatibility, compared to Biomer, in in vitro and ex vivo experiments. Biomer vascular grafts (6 mm I.D. 7 cm in length) were fabricated by a dip coating process. The luminal surface was modified either with PEO grafting, HEMA/STY coating, or Biomer coating (control). These surface-modified grafts were implanted in the abdominal aortas of dogs and evaluated for graft patency and protein adsorption. Surface protein layer thickness was measured by transmission electron microscopy (TEM). B-PEO4K and Biomer showed thick multilayers of adsorbed proteins (1000–2000 A) after 3 weeks to 1 month implantation. In contrast, HEMA/STY only showed a monolayer protein thickness (<200 A), even after 3 months. Visualization of adsorbed plasma proteins (albumin, IgG, and fibrinogen) was performed with scanning electron microscopy (SEM)/TEM using an immunogold double antibody technique. The pattern of protein distribution showed high concentrations of fibrinogen and IgG, and less albumin adsorbed onto Biomer and B-PEO4K. In contrast, HEMA/STY showed a patchy protein distribution pattern with high concentrations of albumin and IgG, and relatively less fibrinogen. Adsorbed monolayer patterns showed improved compatibility over multilayered proteins. The Biomer and B-PEO4K grafts occluded within 1 month, while HEMA/STY grafts were patent for over 3 months. The thin and stable adsorbed protein layer on HEMA/STY surfaces may be associated with the microdomain structures of the surface, and will play an important role in long-term in vivo blood compatibility. This manuscript will evaluate the long-term in vivo performance of these polymers, analyze the extent of protein adsorption onto the surfaces, and correlate protein layer thickness to the thrombogenicity of the polymer surfaces.

Aqueous colloidal dispersions of polyaniline formed by using poly(vinylpyridine)-based steric stabilizers

Abstract: Colloidal polyaniline has been prepared in acidic aqueous media by chemical grafting of polyaniline onto a tailor-made polymeric surfactant. The surfactant, which acts as a steric stabilizer, used in this study is the random copolymer poly(2-vinylpyridine-co-p-aminostyrene). This surfactant contains pendant aniline units which participate in the aniline polymerization, resulting in the formation of sterically stabilized polyaniline particles which have a nonspherical «rice grain» morphology

Acid salts and the structure of ionomers

Abstract: Infrared studies of anhydrous partially and fully neutralized ethylene-co-methacrylic acid copolymer samples are presented. Zinc ions were introduced into the sample by immersion in a dilute solution of diethylzinc in hexane, which results in a material that resembles a «skin-core» composite of a fully neutralized tetracoordinated zinc carboxylate skin and an essentially pure acid copolymer core. At elevated temperatures the fully neutralized zinc salt and the pure acid copolymer mix and the transformation to hexacoordinated zinc carboxylates and zinc acid salts is observed in the infrared spectrum. Significantly, incorporation of a flexible miscible polymer, poly (vinyl methyl ether), reduces the temperature at which this transition occurs. The results are discussed in terms of a series of equilibria. Acid salts are local structures that need to be considered when developing models of ionomers

Copolymerization of Styrene and Ethylene In the Presence of Different Syndiospecific Catalysts

Abstract: Some catalytic systems based on Ti or Zr compounds and methylalumoxane have been investigated with regard to their ability to promote styrene-ethylene copolymerization. 13C NMR analysis shows that the structure and the composition of the copolymerization products are dependent on the catalytic system and on the transition metal/methylalumoxane mole ratio. Polymers containing phenylethylene units bridging polyethylene sequences are generally obtained in the presence of Ti-based catalysts. In the presence of cyclopentadienyltitanium trichloride/methylalumoxane with high A1/Ti mole ratio one can obtain copolymers of ethylene and syndiotactic polystyrene. Zr-based catalyst don't promote copolymerization at all.

Microgel drug delivery system

Abstract: A copolymer microparticle is presented which is derived from at least about 5 weight percent of free carboxylic acid group-containing vinyl monomers, monomers which have a poly(alkylene oxide) appended thereto, oleophilic monomers and other nonionic hydrophilic monomers. Microgels containing these copolymers having a median water swollen diameter of about 0.01 to about 1.0 micrometer are disclosed. Pharmaceutical and diagnostic compositions are disclosed comprising a therapeutic or diagnostic agent and microgels comprising a copolymer derived from at least about 5 weight percent of non-esterified carboxylic acid group-containing vinyl monomers, oleophilic monomers and other nonionic hydrophilic monomers, with the proviso that when the median water swollen diameter of the microgels is 0.1 micrometer or greater, at least 5 weight percent of the monomers have a poly(alkylene oxide) appended thereto. Diagnostic and therapeutic methods are also disclosed wherein the microgels are substantially protein non-adsorbent and substantially refractory to phagocytosis.

Interference microscopy on thin diblock copolymer films

Abstract: Etude de l'orientation des microdomaines lamellaires et de la quantification de l'epaisseur du film qui en resulte pour des films de copolymere styrene/methacrylate de methyle prepares par coulee de solution du polymere sur un substrat de silicium puis recuits au dessus de Tg

Silicone-containing contact lens polymers, oxygen permeable contact lenses and methods for making these lenses and treating patients with visual impairment

Abstract: The present invention relates to novel copolymers and contact lenses made from these copolymers comprising preformed silicon-containing acrylic star polymers and macromonomers, preparation of these contact lenses and a therapeutic method for treating patients with visual impairment. Described is a copolymer comprising at least about 10% by weight of a preformed silicone-containing acrylic copolymer and no more than about 90% by weight of a matrix formed from the random polymerization of a mixture of monomers. The mixture of monomers comprises at least one monomer selected from the group consisting of silicone acrylates, esters of alpha, beta-unsaturated acids and wetting monomers. The preformed silicone-containing acrylic copolymer is preferably copolymerized throughout the matrix. The copolymer is readily machined into gas permeable contact lenses exhibiting substantially enhanced characteristics of at least one of the characteristic group of oxygen permeability, hardness and machineability relative to contact lenses formed from the random polymerization of monomers.

An Introduction to Polymer Colloids

Abstract: Preface.- List of Contributors.- 1. Emulsion Polymerization.- 2. Preparation of Polymer Particles by Dispersion Polymerization.- 3. Polymerization in Inverse Emulsions and Microemulsions.- 4. Copolymer Latex Morphology.- 5. Colloidal Properties of Latex Particles.- 6. Emulsion Polymerization: The Mechanisms of Latex Particle Formation and Growth.- 7. Characterization of Polymer Colloids.- 8. The Rheology of Polymer Colloids.

Anionic polymerization of acrylic monomers. V. Synthesis, characterization and modification of polystyrene-poly(tert-butyl acrylate) di- and triblock copolymers

Abstract: Preparation par polymerisation d'acrylate de t-butyle dans le THF avec un polystyrene vivant. Des polymeres monodisperses sont obtenus quand les anions polystyryl sont modifies par LiCl. Les copolymeres bisequences 50/50 sont constitues de lamelles alternees de polystyrene et de polyacrylate. L'hydrolyse des groupes esters, puis la neutralisation donne des copolymeres styrene/acrylate ionomeres biphasiques