Showing papers on "Polymer published in 1978"

Physical aging in amorphous polymers and other materials

Abstract: The aging of polymeric materials and the alteration of corresponding physical properties are described. -- AATA

Polysiloxane composition and contact lens

Abstract: Monomeric polysiloxanes end-capped with activated unsaturated groups and polymers and copolymers thereof are disclosed herein for use as contact lenses with improved properties, such as, oxygen transportability, hydrolytic stability, biological inertness, transparency and improved strength without the use of fillers. The polymer composition comprises a poly(organosiloxane) α, ω terminally bonded through a divalent hydrocarbon group to a polymerized activated unsaturated group. Contact lenses made therefrom can be, as commonly referred to, "hard" or "soft". This hardness or softness is a function of the comonomer or the molecular weight of the monomers. Preferable the contact lenses are "soft". The copolymer compositions of the instant invention comprise the polymerization product of the polysiloxane monomers and monomer or monomers containing an activated vinyl group. These polymers are employed to make optical products, e.g. contact lenses, intraocular implants, etc.

Composition and process for the treatment of keratin materials with polymers

Abstract: New compositions for the treatment of keratin material, in particular human hair, skin and nails are provided comprising a combination of a cationic polymer with an anionic polymer. Surprisingly the anionic polymer can be retained well on the hair, even after rinsing, when applied with the cationic polymer.

Methods for making microporous products

Abstract: Novel microporous polymers in forms ranging from films to blocks and intricate shapes from synthetic thermoplastic polymers, such as, olefinic, condensation, and oxidation polymers, are disclosed. In one embodiment the microporous polymers are characterized by a relatively homogeneous, three-dimensional cellular structure having cells connected by pores of smaller dimension. Also disclosed is a process for making microporous polymers from such thermoplastic polymers by heating a mixture of the polymer and a compatible liquid to form a homogeneous solution, cooling said solution under non-equilibrium thermodynamic conditions to initiate liquid-liquid phase separation, and continuing said cooling until the mixture achieves substantial handling strength. Also disclosed are microporous polymer products which contain relatively large amounts of functionally useful liquids and behave as solids.

Development of high tensile strength silicon carbide fibre using an organosilicon polymer precursor

Abstract: THE high tensile strength SiC fibre developed in our laboratory1–5 is extremely heat-resistant and its wettability by metals is good. Metal–matrix composites reinforced with the SiC fibre should therefore be of practical use. Polycarbosilane, the precursor of the fibre, is synthesised by thermal decomposition under high pressure of poly dimethylsilane in an autoclave. To produce the SiC fibre on an industrial scale, polycarbosilane needs to be produced in large quantities with high yield. The autoclave method requires a large amount of space, so the operation is inconvenient and uneconomic. We have, therefore, developed a new method of synthesising the polycarbosilane at normal pressure by adding several wt % of polyborodiphenylsiloxane6 to polydimethylsilane. The structure and properties of the new polycarbosilane, and the SiC fibre obtained from it are described here.

CO2 sorption in poly(ethylene terephthalate) above and below the glass transition

Abstract: High-pressure CO2 sorption data in semicrystalline poly(ethylene terephthalate) (PET) are presented for temperatures ranging from 25 to 115°C. The results are described by Henry's law above the glass-transition temperature of PET, while a dual-mode sorption model comprised of a Henry's law and a Langmuir isotherm applies in the glassy state. The disappearance of the Langmuir capacity of the polymer above Tg presumably results from the elimination of regions of localized lower density which are frozen into the glass upon quenching from the rubbery state. Exposure of PET to a high CO2 pressure produced a systematic variation in the apparent sorption equilibria. Correlation of the Langmuir capacity of PET with the dilatometric parameters of the polymer provides a useful framework for understanding the origin of the Langmuir sorption mode and for interpreting annealing and conditioning effects in glassy polymers.

Synthesis of glasses by hot-pressing of gels

Abstract: The synthesis of glasses by hot-pressing of gels was studied for pure SiO2, as well as for La2O3-SiO2 and B2O3-SiO2 systems. It was recognized that gels prepared by hydrolysis and polycondensation of organometallic compounds crystallize less quickly than those obtained from hydrosols, and are, therefore, particularly suited for hot-pressing. Different methods of pressing were investigated; they influence the residual OH− content of resultant glasses. Murrayet al.'s densification model based on viscous flow was found to apply in the case of the gels under study and a dynamic viscosity evaluation is proposed to determine rapidly the pressing parameters for a given gel-glass conversion.

Radiation-grafted hydrogels for biomaterial applications as studied by the ESCA technique.

Abstract: Electron spectroscopy for chemical analysis (ESCA) was used to study the surface composition of several radiation-grafted polymers in both the dry and hydrated (frozen at 160°K) states. Poly(2-hydroxyethyl methacrylate) (HEMA) and polyacrylamide, both hydrophilic polymers, were readily detected in the hydrated or dehydrated states when grafted to polyethylene substrates. For silicone rubber substrates, both grafts were observed on the hydrated surface but were significantly decreased in surface concentration upon dehydration. For grafts on a polyester-urethane, acrylamide was not a major constituent of either the dry or hydrated surface, while HEMA appeared to increase in abundance upon drying. The amount of the hydrophobic poly(ethyl methacrylate) found on the graft surface depended upon the substrate polymer used, but the surface abundance of poly(ethyl methacrylate) was not affected by drying. These results were considered in terms of polar group orientation, polymer chain mobility, substrate permeability, and the limitations of the ESCA technique. The implications of these results with respect to the use of radiation-grafted hydrophilic polymers for biomedical applications are also discussed.

Addition copolymers of lactide and glycolide and method of preparation

Abstract: Relatively high molecular weight, fiber-forming, crystalline copolymers of lactide and glycolide are prepared in a two-stage polymerization process. In the first stage there is prepared a random copolymer of a major proportion of an optically active lactide with a minor proportion of glycolide or d,l-lactide. In the second stage, a major amount of glycolide and a minor amount of lactide monomers are admixed with the copolymer of the first stage and the polymerization resumed until there is obtained a high molecular weight addition copolymer of lactide and glycolide containing from about 50 to 75 wt percent of units derived from glycolide. The polymer is fiber-forming and useful in the preparation of absorbable surgical sutures.

On multiple transverse cracking in glass fibre epoxy cross-ply laminates

Abstract: An investigation has been made of multiple transverse cracking in glass fibre epoxy cross-ply laminates. Four laminates of differing transverse ply thicknesses were investigated. Transverse crack spacing was found to decrease with increasing applied stress and decreasing transverse ply thickness. Very close agreement has been found between the experimental results and a multiple cracking theory based on shear lag analysis in which the plies remain essentially elastically bonded. In these composites a small modulus change is observed at a strain lower than that at which cracking initiated. This phenomenon is associated with a visual, under some circumstances reversible, whitening effect.

Synthesis and Dilute-Solution Behavior of Model Star-Branched Polymers

Abstract: The occurrence of polymers branched in a random fashion is common. Chain transfer reactions can cause short- and long-chain branching in polymerizations such as the high-pressure polymerization of ethylene. Branching can also be introduced intentionally by the use of a polyfunctional monomer in end-linking polymerizations. Similar branching can be produced in addition polymerizations by the use of a small amount of difunctional monomer, e.g., divinylbenzene. There also has been much interest in graft polymerization by which long chain branches can be introduced onto a backbone, which is often a different polymer from the branches. The properties of branched polymers can be quite different from those of linear polymers of the same molecular weight. For example, bulk viscosities as well as concentrated and dilute solution viscosities can be lower for branched polymers than for a linear material of equivalent molecular weight. As an example, the melt processing behavior of polymers can be manipulate...

A class of mathematical models for sorption of swelling solvents in glassy polymers

Abstract: A class of mathematical models for sorption of swelling solvents in glassy polymers is analyzed. The essential features of these models are the explicit consideration of the kinetics of swelling and of the driving force for swelling. It is shown that, even when all other elementary phenomena are modeled in the simplest possible way, all the experimentally observed features of the processes considered are correctly predicted.

Polymer emulsification process

Abstract: A polymer emulsification process comprising intimately dispersing a liquified water insoluble polymer phase in an aqueous liquid medium phase containing at least one nonionic, anionic or cationic oil-in-water functioning emulsifying agent, in the presence of a compound selected from the group consisting of those hydrocarbons and hydrocarbyl alcohols, ethers, alcohol esters, amines, halides and carboxylic acid esters which are inert, non-volatile, water insoluble, liquid and contain a terminal aliphatic hydrocarbyl group of at least about 8 carbon atoms, and mixtures thereof, and subjecting the resulting crude emulsion to the action of comminuting forces sufficient to enable the production of an aqueous emulsion containing polymer particles averaging less than about 0.5 μ in size.

Polysiloxane shaped article for use in biomedical applications

Abstract: Monomeric polysiloxanes end-capped with activated unsaturated groups and polymers and copolymers thereof are disclosed herein for use as contact lenses and biomedical devices with improved properties, such as, oxygen transportability, hydrolytic stability, biological inertness, transparency and improved strength without the use of fillers. The polymer composition comprises a poly(organosiloxane) monomer α,ω terminally bonded through divalent hydrocarbon groups to polymerized free radical polymerizably activated unsaturated groups. Contact lenses and biomedical devices i.e. shaped article for use in biomedical applications made therefrom can be "hard" or "soft". This hardness or softness is a function of the comonomer or the molecular weight of the monomers. Preferably the contact lenses and biomedical devices are "soft". The copolymer compositions of the instant invention comprise the polymerization product of the polysiloxane monomers and monomer or monomers containing an activated vinyl group. These polymers are employed to make biomedical devices and optical products, e.g. contact lenses, intraocular implants, etc.

Relationship between structure and mechanical properties in rubber‐toughened epoxy resins

Abstract: Toughened polymers were prepared by adding CTBN rubbers to DGEBA-type epoxy resins. Structure was varied by altering the type and concentration of hardener, the initial molecular weight of the resin, the amount of Bisphenol A added, and the conditions of cure. Electron microscopy showed that these factors affected both particle size and degree of phase separation: rapid curing inhibited phase separation, and produced small particles. Increasing the molecular weight of the resin, either directly or by reaction with Bisphenol A, improved phase separation. Dynamic mechanical measurements of rubber phase volume proved possible, although Tg of the CTBN rubber coincided with a β process in the epoxy resin. Fracture resistance, measured by GIC, increased linearly with rubber phase volume. Creep and yield behaviour were also affected by the degree of phase separation.

Contact electrification of polymers: A quantitative model

Abstract: An explicit model of contact‐charge exchange in polymers is proposed in which the steady‐state exchanged charge resides in intrinsic molecular‐ion states. The eigenvalue spectra of these states are inferred from metal/polymer contact‐charge measurements using a theoretical formalism constructed for this purpose. This model of metal/polymer contact‐charge exchange is extended to encompass the description of polymer/polymer contact‐charge exchange as well. Utilizing the metal/polymer contact‐charge‐exchange spectra as input data, the model predicts correctly both the sign and order of magnitude of measured contact‐charge exchange between polystyrene and copolymers of styrene and methyl methacrylate.

The interaction of ethidium with synthetic double-stranded polynucleotides at low ionic strength

Abstract: The interaction of ethidium with synthetic DNA and RNA double-stranded polymers at 0.01 M ionic strength, pH 7.0, has been studied by fluorimetry at low drug to nucleotide ratios. Binding constants have been calculated assuming an excluded-neighbouring site model for the interaction of ethidium with double-stranded polymers. The values obtained are poly d(AT).poly d(AT), 9.5 X 10(6) M-1; poly dA.poly dT, 6.5 X 10(5) M-1; poly d(GC).poly d(GC), 9.9 X 10(6) M-1; poly dG,poly dC, 4.5 X 1-(6) M-1; poly d(AC); poly d(GT), 9.8 X 10(6) M-1; poly d(AG).poly d(CT), 1.3 X 10(6) M-1; poly rA.poly rU, 4.1 X 10(7) M-1. The displacement of ethidium from poly d(AT).poly d(AT) by 9-aminoacridine and an acridine-containing antitumor agent (NSC 156303; 4'-(9-acridinylamino)methanesulphon-m-anisidide) has also been examined.

Optimized Rouse–Zimm theory for stiff polymers

Abstract: Earlier, the authors proposed a method for constructing an optimized Rouse–Zimm theory for an arbitrary polymer system. This method is applied here to a model of a stiff polymer. The spectrum of relaxation times and the intrinsic viscosity obtained from the optimized Rouse–Zimm theory are discussed. Comparison with known results for the limiting cases of a flexible chain, a rigid ring, and a rigid rod, shows that this procedure gives a quite good approximation at low frequencies. Its basic disadvantage is its inability to account for the observed high frequency behavior of the intrinsic viscosity of stiff polymers.

Reversible flocculation of sterically-stabilised dispersions

Abstract: Because of the existence of a shallow minimum in the interaction energy against particle separation diagram for neutral, sterically-stabilised particles, dispersions of such particles exhibit reversible flocculation above a threshold particle number concentration. The equilibrium state achieved is one in which a “floc phase” co-exists with a “dispersed phase”. By analogy with related phase separation processes in molecular systems the critical particle number concentration for flocculation is shown to be temperature dependent. An equivalent statement is that the critical flocculation temperature is dependent on the particle number concentration. Temperature phase diagrams have been constructed for the system: neutral polystyrene latex particles carrying anchored, low molecular weight poly(ethylene oxide) chains, dispersed in various concentrations of aqueous MgSO4 solutions.Reversible flocculation may also be achieved by adding polymer to the continuous phase, at a given temperature. A “three-component” phase diagram has been constructed for the system: polystyrene latex particles carrying anchored poly(ethylene oxide) chains as above, plus water, plus free poly(ethylene oxide) molecules of varying weight.A preliminary, thermodynamic analysis of the results is presented.

Mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts

Abstract: A mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts is developed which differs significantly from previous mechanisms in the proposal that it proceeds via a 1,2-hydrogen shift from the α-carbon of the polymer chain and formation of metallocycle and carbene intermediates.

The radiation improvement of polyethylene prostheses. A preliminary study

Abstract: The radiation crosslinking of high-density polyethylene prostheses was investigated over a wide range of doses in the presence and absence of gaseous crosslinking agents. It was found that in the bulk polymer the crosslinking pattern is completely different from the homogeneous crosslinking that occurs in polymer films. The presence of crosslinking agents causes highly crosslinked polymer to be formed on the surface while the bulk of the polymer is largely unaffected--which is explained in terms of diffusion phenomena. This surface crosslinking has a profound effect on the mechanical properties of the prostheses and restricts cold flow and deformation of the polymer without sacrificing the excellent abrasion-resistance properties of the polyethylene when subjected to high pressures. Based on this research a number of high-density polyethylene knee prostheses have been radiation-crosslinked and the results in vitro appear to be very promising.

Combination of ethylene polymer, polymer having alkyl side chains, and nitrogen containing compound to improve cold flow properties of distillate fuel oils

Abstract: Oil soluble combinations of (A) ethylene polymer or copolymer, (B) a second polymer having alkyl side chains of 6 to 30 carbon atoms, and derived from carboxylic acid esters and/or olefins, and (C) nitrogen compounds, such as amides, amine salts and ammonium salts, of carboxylic acids or anhydrides, are useful in improving the cold flow properties of distillate hydrocarbon fuel oils.

Water-insoluble hydrophilic copolymers

Abstract: A water-insoluble hydrophilic gel comprising: (A) about 30 to about 90% of a hydrophilic (a) polymer of identical or different water-soluble mono-olefinic monomers, or (b) copolymer of said water-soluble monomers with 1 to 70% of water-insoluble, identical or different mono-olefinic monomers, which polymer or copolymer is cross-linked with (B) about 10 to about 70% of a terminal diolefinic hydrophobic macromer having a molecular weight from about 400 to about 8000.

Polymer–Polymer Compatibility

Abstract: Publisher Summary This chapter provides an overview of polymer-polymer compatibility. The term "polymer compatibility" refers to the total miscibility, on a molecular scale, of homo-polymers and of random copolymers with each other in various combinations. In the chapter, no distinction is made between polymers in the rubbery or glassy state. The chapter discusses the crystallizable polymers in which the polymer remains at least partially amorphous and in which the miscibility with other polymers are investigated in the amorphous state. The chapter briefly reviews methods for predicting compatibility and presents a method for predicting compatibility along with its limitations. It explains the prediction schemes for polymer-polymer compatibility. The experimental methods for determining solubility parameters of polymers involve studies of the polymers in solution or swollen by solvent, that is, the thermodynamics of the situation involves the entropy contribution to the polymer-solvent interaction parameter and it complicates the theoretical treatment. It often turns out that experimental solubility parameters for the same polymer vary a great deal, depending both on the method used and on the experimenter. The two methods used are (1) swelling of a cross-linked polymer, where it is assumed that the solubility parameter of the polymer is equal to that of the solvent which swells it most highly and (2) intrinsic viscosity of a soluble polymer sample, where the solubility parameter of the polymer is equal to that of the solvent in which its intrinsic viscosity is greatest. For the same polymer, these methods often give different results depending on the nature of the solvents, which may be non-polar, polar, or hydrogen bonding.