Showing papers on "Polymer published in 1990"

Preparation of phospholipid polymers and their properties as polymer hydrogel membranes.

Abstract: A methacrylate monomer having the phospholipid polar group, 2-methacryloyloxyethyl phosphorylcholine (MPC) was prepared by an improved method with good yield. MPC was copolymerized with n-butyl methacrylate (BMA). The polymer membranes were prepared from the poly(MPC-co-BMA) by a solution casting method. The membrane adsorbed water well and became a hydrogel structure even MPC mole fraction in the copolymer was 0.04. The water content of the hydrogel membrane increased with increase of MPC units and rise of temperature. These properties of the hydrogel membrane were attributed to the highly hydrophilic phospholipid polar group in the copolymer. Water soluble organic compounds and proteins whose molecular weights were below 104 permeated through the hydrogel membrane. However, the protein could not permeate when the molecular weight was higher than 105.

Kinetics of swelling and shrinking of gels

Abstract: The kinetics of swelling and shrinking of gels is theoretically generalized and experimentally studied. A new relation, in addition to the differential equation developed by Tanaka and Fillmore, is formulated to solve the kinetics of gels having arbitrary shape. Using our new theory, we provide explicit solutions for long cylinder and large disk gels. These solutions predict that the effective diffusion constants of long cylinder and large disk gels are 1.5 and 3 times smaller than that of a spherical gel. The relaxation times of long cylinder and large disk gels with small shear modulus μ are approximately 2.0 and 5.7 times longer than that of a sphere, where the diameters of the cylinder and the sphere and the thickness of the disk are the same. The theory also concludes that the experimentally measured kinetics of a long cylinder and disk gels along the z axis and the radial axis are the same. The results have been excellently confirmed by the experiments.

Polymers in solution

Abstract: The authors discuss the physical nature of interactions between linear flexible chains in a solvent. They review the results obtained on the structure of polymer solutions, with the help of the observation techniques and conceptual approaches developed since 1965. Comparison between observed and predicted behaviour is made for values of the critical exponents and the universal amplitude.

Single-chain transition of poly(N-isopropylacrylamide) in water

Abstract: The temperature dependence of the radius of gyration and the hydrodynamic radius or poly(N-isopropylacrylamides) with various molecular weights (1.63×10 6 -2.52×10 7 ) in water was obtained in the relatively good through poor regions by use of static and dynamic light scattering techniques. The dimensions of the polymer show sharp decreases in the poor solvent (collapsed) region. The observed transition in polymer dimensions is analyzed in terms of a coil-globule transition, which is one of the most important problems of polymer solution physics. Reasonable agreement with the theoretical predictions is obtained. This water-soluble polymer system shows a fairly narrow crossover region compared with the polystyrene systems

Chain structure, phase morphology, and toughness relationships in polymers and blends

Abstract: We present chain structure, phase morphology, and toughness relationships in thermoplastic polymers and polymer/rubber blends. In neat polymers, molecular aspects of craze/yield behavior are controlled by two chain parameters: entanglement density ν e and characteristic ratio C ∞ . The crazing stress is proportional to ν e 1/2 , and the yield stress is proportional to C ∞ . The dispersed rubber toughens a polymer/rubber blend mainly by promoting energy dissipation of the matrix. The toughening efficiency correlates with the rubber phase morphology and the chain structure of the matrix

Electrochemical biosensor based on immobilized enzymes and redox polymers

Abstract: The present invention relates to an electrochemical enzyme biosensor for use in liquid mixtures of components for detecting the presence of, or measuring the amount of, one or more select components. The enzyme electrode of the present invention is comprised of an enzyme, an artificial redox compound covalently bound to a flexible polymer backbone and an electron collector.

Two-parameter scaling for polymers in Θ solvents

Abstract: We revive an old conjecture that a fixed number of binary contacts between chains collec- tively make up the topological constraint commonly referred to as an entanglement. This leads us to a general scaling theory for semidilute polymer solutions which involves two length scales, the screening length ( and the tube diameter a. In good solvents these two lengths have the same concentration depen- dence and we recover the de Gennes results. In 9 solvents the two length scales depend on concentration differently. Combining the concentration dependences of these two length scales with concepts from the- ories of rubber elasticity and reptation leads to new predictions for the plateau modulus G - kT/(a2{) - c7/3 and viscosity 9 - M2/3(c/c*)14/3 in 9 solvents, where M is the polymer molecular weight and c* is the overlap concentration. These predictions are found to compare favorably with available experimental data.

Genetic engineering of structural protein polymers

Abstract: Genetic and protein engineering are components of a new polymer chemistry that provide the tools for producing macromolecular polyamide copolymers of diversity and precision far beyond the current capabilities of synthetic polymer chemistry. The genetic machinery allows molecular control of chemical and physical chain properties. Nature utilizes this control to formulate protein polymers into materials with extraordinary mechanical properties, such as the strength and toughness of silk and the elasticity and resilience of mammalian elastin. The properties of these materials have been attributed to the presence of short repeating oligopeptide sequences contained in the proteins, fibroin, and elastin. We have produced homoblock protein polymers consisting exclusively of silk-like crystalline blocks and elastin-like flexible blocks. We have demonstrated that each homoblock polymer as produced by microbial fermentation exhibits measurable properties of crystallinity and elasticity. Additionally, we have produced alternating block copolymers of various amounts of silk-like and elastin-like blocks, ranging from a ratio of 1:4 to 2:1, respectively. The crystallinity of each copolymer varies with the amount of crystalline block interruptions. The production of fiber materials with custom-engineered mechanical properties is a potential outcome of this technology.

Article having non-crosslinked crystallized polymer coatings

Abstract: A non-crosslinked crystallized polymer or polymer blending coating is disclosed for articles that come into contact with bodily fluids. The polymer or polymer blend to be used is crystallizable and is stable in the presence of water at temperatures of up to about 60° C. when in the crystalline state. The polymer or polymer blend is dissolved in a solvent, such as water or dimethyl sulfoxide (DMSO), and is coated on the article. The polymer coating is then crystallized, generally by heat treatment, providing both toughness and increased adherence of the coating to the article without ready dissolution when the article comes into contact with fluids.

Polymer Blends Containing Liquid Crystals: A Review

Abstract: This paper reviews the literature of polymer blends containing low and high molar mass liquid crystals. Low molar mass liquid crystals have been used as plasticizers for thermoplastic polymers and in applications such as electro-optics, optical recording media, and membranes. High molar mass liquid crystalline polymers have been primarily used in polymer blends as processing aids and as an incipient reinforcing phase for “self-reinforced” materials. This review discusses the phase behavior, rheology, and mechanical properties of these blends.

Molecular weight and polydispersity effects at polymer-polymer interfaces

Abstract: We study the interfacial properties of immiscible polymers, going beyond the usual approximation of infinite molecular weight, complete immiscibility. For finite molecular weights, the interfaces are broader and the interfacial tensions smaller than predicted by this approximation. These corrections are entropic effects and are significant for typical experimental stituations: they are in fact inversely proportional to the incompatibility χ AB N, where χ AB is the Flory interaction parameter between unlike (A and B) monomers and N the number of monomers per chain. In polydisperse systems, small chains accumulate slightly at the interface, lowering the interfacial tension

Positron annihilation in amine‐cured epoxy polymers—pressure dependence

Abstract: Positron annihilation spectroscopy has been used to study free volume in an arnine-cured epoxy as a function of external pressure at temperatures above and below the glass transition temperature. The observed ortho-positronium lifetime τ3 and formation probability I3 decreased with increasing pressure. The decrease in τ3 is interpreted in terms of a corresponding decrease in average free-volume hole size over the range from 0.135 to 0.045 nm3. The fractional free-volume and the free-volume compressibility in the epoxy are calculated as functions of pressure at 100°C.

Anti-infective and antithrombogenic medical articles and method for their preparation

Abstract: An anti-infective medical article has chlorhexidine bulk distributed throughout a polyurethane base layer and may have a coating layer on the base layer. The coating layer may be chlorhexidine permeated into the surface or it may be an antibiotic, antithrombogenic agent or a polymeric surface layer laminated onto the base layer. The invention includes a method for preparing the article wherein a homogeneous melt of polymer and chlorhexidine is prepared by twin screw compounding and the melt is extruded to give a medical article having bulk distributed chlorhexidine.

Organic aerogels: microstructural dependence of mechanical properties in compression

Abstract: Aerogels are a unique class of ultrafine cell size (<1000 A), low-density foams. These materials have continuous porosity and a microstructure composed of interconnected colloidal-like particles or chains with characteristic diameters of 100 A. Traditional aerogels are inorganic, made via the hydrolysis and condensation of metal alkoxides (e.g. tetraisopropoxy titanate). Recently, the authors reported the development of organic aerogels from the sol-gel polymerization of resorcinol with formaldehyde. Because these new aerogels are composed of a highly crosslinked aromatic polymer, they can be pyrolyzed in an inert atmosphere to form vitreous carbon aerogels. This work describes how the microstructure of these organic aerogels can be manipulated and controlled. The microstructural dependence of the compressive mechanical properties of both resorcinol-formaldehyde and carbon aerogels is examined in detail.

Phase separation in polystyrene latex interpenetrating polymer networks

Abstract: Polystyrene/polystyrene latex interpenetrating polymer networks (IPNs) were prepared by seeded emulsion polymerzation of styrene–divinylbenzene mixtures in crosslinked monodisperse polystyrene seed latexes. The resulting latexes comprised uniform nonspherical particles, which were formed by separation of the second-stage monomer from the crosslinked seed network during swelling and polymerization. The kinetics of phase separation were investigated by examining the changes in particle morphology using optical microscopy, which revealed that the phase separation was induced by the relaxation of the polymer chains before polymerization began and was enhanced by increased conversion. The thermodynamics of phase separation were investigated by analysis of the free-energy changes during swelling and polymerization, and the phase separation was described by a nucleation-and-growth mechanism. The results of this study have been applied to the design and synthesis of a series of uniform nonspherical particles of different morphology.

Aqueous-liquid and blood-absorbing powdery reticulated polymers, process for producing the same and their use as absorbents in sanitary articles.

Abstract: A powdery, water-insoluble, reticulated resin that absorbs aqueous or serous liquids, as well as blood, is composed of (a) 55-99.9 % by weight of polymerized, insaturated, polymerizable, acid-group containing monomers, of which at least 25 mol. % are neutralized; (b) 0-40 % by weight of polymerized insaturated monomers that can be copolymerized with (a); (c) 0.1-5.0 % by weight of a cross-linking agent and (d) 0-30 % by weight of a water-soluble polymer, the weight percentages of (a) to (d) refering to the water-free polymer. This polymer is characterized by the fact that the resin powder is coated with 0.1 to 5 % by weight of an alkylene carbonate, referring to the resin powder, and is heated up to a temperature between 150 and 300 °C. A process for producing this polymer is also disclosed, as well as its use in sanitary articles such as diapers and the like and in absorbent structures composed of hydrophilic fibres and an absorbent resin.

Morphology development of polymeric microparticles in aqueous dispersions. I. Thermodynamic considerations

Abstract: A thermodynamic analysis of polymer particle morphology highlights the role of interfacial tensions in controlling particle structure. The influence of the surfactant and the nature of the incompatible polymers is seen through their individual and collective effects upon these interfacial tensions. It has been found that by simply changing the type of surfactant used in the emulsion the particle morphology can change from core-shell to hemispherical, in agreement with thermodynamic predictions. Several apparently different morphologies (hemispherical, sandwich, multiple lobes) have been found to coexist at the same time within a single emulsion, suggesting that they may be simply different states of phase separation and not thermodynamically stable, unique morphologies. The thermodynamic analyses are independent of particle size and method of emulsion processing. Experimental evidence shows that the morphology of particles formed via in situ polymerization (as in a synthetic latex) is controlled by interfacial tensions in the same manner as those particles formed via solvent evaporation from a solution of an incompatible polymer pair (as in an artificial latex or microencapsulation).

Reactive silicone and/or fluorine containing hydrophilic prepolymers and polymers thereof

Abstract: Vinyl unsaturated copolymers are described which are obtained in a two-step process and which consist of monomeric units A, B, C, D and E, copolymerized in a first step, and in a second step reacted with a reactive vinyl monomer M v , and in which A is a siloxane or fluorine containing vinyl monomer, 30-70% by weight; B is N,N-dimethylacrylamide or N-vinylpyrrolidone, 30-70% by weight; C is an active hydrogen containing vinyl monomer, 0.5-25% by weight; D are other copolymerizable comonomers, 0-30% by weight, and E is a chain transfer agent, 0-10 mol percent. M v is a vinyl unsaturated isocyanate. These vinyl unsaturated polymers are useful, either by themselves or in combination with other copolymerizable vinyl monomers, as heat or UV-curable coatings or glass, plastic, wood, paper, textiles, metal or ceramics, said coatings possessing low surface energies and low refractive indices. They are especially useful as UV-curable hydrophilic coatings and water-swelling biocompatible polymers, especially fully molded highly oxygen-permeable contact lenses.

Template synthesis of organic microtubules

Abstract: Organic microtubules have recently caused a great deal of excitement in the physics, chemistry, and materials science communities. Such tubules are inherently intriguing chemical systems and have myriad proposed technolgical applications; they may also be useful as mimics of biological microtubules. The only known synthetic route for preparing organic microtubles involves extremely expensive reagents and produces tubules with a broad range of diameters and lengths. The authors have recently discovered a new method for synthesizing organic microtubules. This method uses a microporous membrane as a template during tubule synthesis. The most significant advantage of this template method is that it yields tubules with monodisperse diameters and lengths. They describe this template synthetic method in this paper.