Showing papers on "Polymer published in 1975"

Melting Point Depression and Kinetic Effects of Cooling on Crystallization in Poly(vinylidene fluoride)-Poly(methyl methacrylate) Mixtures

Abstract: Thermal analysis of solution cast mixtures of poly(viny1idene fluoride) (PVF2) and poly(methy1 methacrylate) (PMMA) has been carried out with various programmed temperature profiles. Results from experi- ments conducted in a quasi-equilibrium state show that PVF:! crystallizes in the mixture upon cooling. Further- more, depressions were observed in the melting and the crystallization temperatures. The melting point depression phenomenon is found to be explicable in terms of thermodynamic mixing of a crystalline polymer with an amor- phous polymer. To this end, an analytical expression appropriate to the crystalline-amorphous polymer pair is de- rived from Scott's equation for thermodynamic mixing of two polymers. From this expression the interaction pa- rameter for the polymer pair is found to be -0.295 at 16OoC, indicating that the system is compatible in the molten state. The depression of crystallization temperature which depends strongly on both the composition and the cool- ing rate is attributed to the ability of the PVF2 segments to migrate and to the change of composition in the melt during crystallization. For mixtures with a PVF2 content by weight of less than 0.5, it is possible to suppress the crystal transformation at room temperature with a moderate cooling rate. Finally, it is pointed out that because of the strong kinetic effects of cooling on the thermodynamic state of the mixture, caution should be exercised in the calorimetric study of compatibility of the polymer pair.

Structure and properties of oriented polymers

Abstract: Introduction Physicochemical Approaches to the Measurement of Molecular Anisotropy Structure and Morphology of Oriented Polymers Infrared Dichroism, Polarised Fluorescence and Raman Nuclear Magnetic Resonance Mechanical Anisotropy at Small Strains Anisotropic Creep Behaviour Anisotropic Yield Behavior Film Formation Liquid Crystalline Polymers Index

Oriented crystallization of polymers

Abstract: Molten crystallizable polymer is extruded through an orifice. Opposite the orifice on the upstream side is a fixed surface arranged so as to provide in the molten polymer a line of uniaxial extension or a plane of pure shear passing through the orifice. The polymer is extruded at a temperature and flow rate such as to cause a core of crystalline polymer to form in the melt along said line or plane. It is particularly suitable for extruding a continuous filament having a highly crystalline core in a generally less crystalline matrix of the polymer.

The Lagrangian theory of polymer solutions at intermediate concentrations

Abstract: 2014 De Gennes has shown that the properties of an isolated polymer in a solution (a chain with excluded volume) can be deduced within the framework of a Lagrangian theory for a zero component field in the absence of an external field. This result in generalized to the case of polymer solutions at intermediate concentrations. It is shown that a grand ensemble of polymers can be described by using a Lagrangian theory for a zero component field coupled to an external field. The concentrations Cp of polymers (chains) and Cm of monomers (links) are fixed by two chemical potentials. It is shown that the osmotic pressure obeys a scaling law of the form (P/KTCp) = F(Cp N303BD) where N is the mean number of monomers per polymer (N = Cp/Cm) and 03BD the critical index defining the size of a long isolated polymer. The function F(03BB) can be expanded in powers of 03BB and it is given implicitly by the generating functional of the zero-momentum vertex functions derived from the Lagrangian theory. The results seem to be in good agreement with experiments. Tome 36 N° 4 AVRIL 1975 Classification Physics Abstracts 1.650 7.480

Water-reduced urethane coating compositions

Abstract: A water-diluted, ungelled, non-sedimenting polyurethane and a process for preparing such a polyurethane in an aqueous medium is disclosed. High molecular weight thermoplastic products are obtained by chain extending in aqueous medium an NCO polymer having a salt group equivalent weight of 6000 or less and substantially free of reactive hydrogen. The average functionality and equivalent ratio of the polyisocyanate and active hydrogen-containing materials used in making the NCO polymer, as well as the functionality of the chain extender, are carefully controlled so as to get high molecular weight ungelled products. Thermosetting compositions can be made by adding curing agent to the chain extended material. Curing agents can also be incorporated into the polymer molecule either in the making of the partially reacted NCO-containing prepolymer or by further reaction with the partially reacted NCO-containing prepolymer. The water-dispersed polyurethanes of the present invention are excellent film formers, capable of making coatings with a wide spectrum of desirable properties. In addition, they can be added to other water-compatible compositions to improve flexibility, hardness, drying and other coating properties.

Multilayer membrane useful as synthetic skin

Abstract: A multilayer membrane, which is useful as synthetic skin, is disclosed herein. A first layer is formed from a material which does not provoke an immune response and which is also insoluble and nondegradable in the presence of body fluids and/or body enzymes. Preferred materials for the first layer are crosslinked composites of collagen and a mucopolysaccharide. A second layer is formed from a nontoxic material which controls the moisture flux of the overall membrane to about 0.1 to 1 mg./cm 2 /hr. Suitable materials for the second layer include synthetic polymers such as silicone resins, polyacrylate or polymethacrylate esters or their copolymers, and polyurethanes.

The Effects of Surface Chemical Interactions on the Properties of Filler-Reinforced Rubbers

Abstract: 1. Heat treatment of carbon black-rubber mixtures is a method of “in process” polymer grafting which gives a definite improvement in the dynamic properties of vulcanizates. 2. The heat treatment process can be more effective if chemical promoters are used. These chemical promoters function as coupling agents between filler surface and rubber. 3. With very unreactive butyl rubber an effective interaction is produced both by the addition of chemical promoters and by the use of specially active surface-modified carbon black. 4. In normal unsaturated rubbers, surface modifications of carbon black with a wide variety of groups has shown only minimal effects on rubber-reinforcing ability. Halogenated blacks have a pronounced effect on vulcanization kinetics, giving cured vulcanizates of high crosslink density. 5. Carbon black surfaces can be deactivated by calcining at high temperatures. The loss of surface-bound hydrogen may not account for this loss in surface activity. 6. Grafting of polymers to the...

Polymer Compatibility by Gas-Liquid Chromatography

Abstract: Reliable methods for identifying soluble polymer pairs have long been limited to the solid state even though the possibility exists that a pair of polymers which is immiscible in the solid is miscible in the melt. Inverse chromatographic procedure has been used to study polymer-polymer miscibility in the molten state. Results for poly( 6-capro1actone)-poly(viny1 chloride) blends indicate that complementary dissimilarity is the rule of polymer compatibility when specific interacting forces are involved. Such forces in PCL-PVC blends are of the same order of magnitude as those between PVC and its usual plasticizers. When these results are combined with earlier treatments of Flory equation of state, it turns out that variation of mixture parameters leads to bimodality of the phase diagram as well as asymmetry of the critical concentration. In the study of polymer compatibility, reliable methods for the identification of soluble polymer pairs are applicable in the solid ~ t a t e ; ~ , ~ ~ those applicable in the melt are generally limited by experimental difficulties. Microscopic methods are applicable only where there are substantial differences in refractive indices and light scattering techniques, including the recently developed pulse-induced critical ~ c a t t e r i n g , ~ are applicable for polymer-solvent systems only. Yet, it is conceivable that two polymers would be miscible in the melt but not in the solid on account of morphological differences, thermodynamic or kinetic changes accompanying crystallization, or vitrification or mere temperature effects on solubility. It is of interest to identify these systems; furthermore, it may be possible to induce miscibility down to the solid state via chemical or physical means. Gas-liquid chromatography (GLC) has received general recognition as an effective simple technique for rapid measurement of polymer-solvent interaction and solvent activity coefficient in molten homopolymers.4-1z I t has also been used in determining such properties10 as the glass transition phenomena and the glassy state, crystallinity, adsorption isotherms, heats of adsorption, surface area, interfacial phenomena, diffusion coefficients, and complex equilibria in solution as well as curing processes in nonvolatile thermoset systems. For these type applications, Guillet has suggested”J2 the name “inverse gas chromatography” based on the fact that conventional usage of GLC determines the property of an unknown sample in the moving phase with a known stationary phase whereas inverse chromatography determines the properties of an unknown stationary phase with the aid of a known vaporizable solute in the moving phase. He considers the latter as a “molecular probe’) experiment where the vaporizable molecules are designated “probe” molecules. In this paper, we describe an inverse chromatographic procedure whereby studies of two homopolymers and their blends, analyzed in terms of Scott’s ternary solution treatment13 of the Flory-Huggins theory,14 yield the polymer-polymer interaction parameter. Relative measures of various contributions such as polar, complexing and noncomplexing interactions are obtained based on the most significant strength of selected probe molecules. Four types of polymer interactions investigated are: (i) proton accepting strength, probed with chloroform and ethanol; (ii) proton donor strength with methyl ethyl ketone and pyridine; (iii) polar strength with acetonitrile and fluorobenzene; (iv) nonpolar strength with hexane and carbon tetrachloride. The division and choice of solutes are based on the relative magnitude of dipole moments, polarizabilities, and hydrogen bonding capabilities. It is recognized, though, that no such clear-cut division exists and tha t association complexes stabilized by electronic and/or electrostatic interactions are possible15 with all the probe molecules chosen. What is proposed is a scale of interaction by which the relative strength of different polymers could be measured. Plausible indices of interaction are the FloryHuggins interaction parameter,14 xil, its counterpart based on conditions of an hypothetical liquid at O’K, xLj*, or the exchange energy parameter of Flory equation of state,1621 XL, . The usual sign convention is assumed; i.e., a large positive value indicates unfavorable interaction, a low value indicates favorable interaction, while a negative value indicates a rather strong specific interaction. A nonpolar probe would generally yield positive quantities representative of noncomplexing contributions whereas specific interacting probes could yield negative values. The total specific interactions of such probes with a stationary solvent comprise54 at least four different kinds: 7~ electrons, dipolar, n electron, proton donor-acceptor interactions. These are, therefore, the basic interpretative concepts that will be applied in the discussion. The above procedure has been applied to poly(viny1 chloride) (PVC), poly(ecapro1actone) (PCL), and their blends. The results indicate that complementary dissimilarity is the rule of polymer miscibility when specific interacting forces are involved. Such forces in PCL-PVC blends are of the same order of magnitude as those between PVC and its usual plasticizers. When these results are combined with McMaster’s applicationzz of Flory equation of state16 z1 to polymer-polymer phase relations, asymmetry of the critical concentration as well as bimodal lower critical solution temperature (lcst) behavior are predicted. Experimental Section Apparatus. A Micro-Tek 2500R gas chrqmatograph equipped with thermal-conductivity detector was used for this study. Temperatures of the injection block, column outlet block, and detector cell were monitored by pyrometer but the column temperature was doubly checked with a Digitec Model 551-4 plug-in platinum resistance thermometer. The average error in column temperature is f0.5’. Flow rate of the helium carrier gas, controlled by a MicroTek regulator valve, is measured by a soap-bubble flowmeter. Column pressure was measured differentially against the atmospheric outlet pressure with a U-tube manometer filled with mercury. The elution profiles were recorded by a Honeywell Electronik 19 chart recorder. Column Preparation. All stationary phases were coated onto Fluoropak-80, 60-80 mesh, by dissolution in appropriate solvent and slow evaporation in a Breeze-Away Packing Dryer (Chemical Research Services, Inc.) which is essentially a fluidized bed. The coated support was packed by a gentle tapping procedure into a 5 ft X 0.25 in. 0.d. stainless steel silanized tubing, the ends of which were loosely plugged with glass wool. The tubing was then coiled to fit the oven chamber. After each experiment, the weight of polymer used was determined by 1-week extraction with refluxing solvent in a Soxhlet extractor equipped with ceramic thimble. Vol. 8, No. 3, May-June 1975 Polymer Compatibility by Gas-Liquid Chromatography 317 Table I Polymer Coating Analysis Table I1 Characteristic Parameters for Solvents and Polymers

Preparation of low and medium density ethylene polymer in fluid bed reactor

Abstract: A supported catalyst is used in the low pressure catalytic copolymerization of ethylene with C 3 to C 6 α-olefins in a fluid bed reactor to produce polymers having a density of less than 0.941 and a melt index of >0.0 to at least about 2.0. The supported catalyst contains about 0.05 to 3.0 weight % of chromium, about 1.5 to 9.0 weight % of titanium and >0.0 to about 2.5 weight % of fluorine.

Piperazine based polymer and hair treating composition containing the same

Abstract: Piperazine-based low molecular weight film-forming cationic polymer is employed in a cosmetic hair-conditioner composition comprising a solution of the polymer in amounts of about 0.1-5 weight percent of the composition in a solvent such as water, acidified water, or aqueous alcohol solution.

Tough thermoplastic polyester compositions

Abstract: Toughened multi-phase thermoplastic composition consisting essentially of one phase containing 60 to 99 percent by weight of a polyester including polycarbonate matrix resin of inherent viscosity of at least 0.35 deciliter/gram, and 1 to 40 percent by weight of at least one other phase containing particles of at least one random copolymer having a particle size in the range of 0.01 to 3.0 microns and being adhered to the polyester, the at least one random copolymer having a tensile modulus in the range of 1.0 to 20,000 p.s.i., the ratio of the tensile modulus of the polyester matrix resin to tensile modulus of said at least one polymer being greater than 10 to 1. Said at least one polymer is either a branched or straight chain polymer. The toughened compositions are useful for making molded and extruded parts. Such parts possess greater ductility, less reduction in toughness from scratches and molded in notches and reduced susceptibility to catastrophic failure when compared to known melt fabricated materials.

Thermoplastic urethane elastomers. I. Effects of soft‐segment variations

Abstract: A series of thermoplastic urethane elastomers with soft segments of varying sequence length was prepared and their dynamic mechanical properties were characterized over a wide temperature range. The polymers were prepared using various molecular weight polycaprolactone diols as the soft segment and 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segment. The urethane elastomer exhibited soft-segment crystallization when a polycaprolactone diol greater than 3000 Mn was used. The glass transition temperature of these materials progressively shifted to lower temperatures as the chain length of the soft segment was increased. This dependence was interpreted in terms of a molecular weight relationship similar to that associated with amorphous homopolymers. The dynamic mechanical properties of these polyurethanes appear to be consistent with responses observed for compatible copolymers.

The effects of chemical structure and surface properties of synthetic polymers on the coagulation of blood. IV. The relation between polymer morphology and protein adsorption.

Abstract: Although these studies are preliminary, they do not show that the chemical structure of the block copolymer is not the only determinant of its blood properties; one must be equally concerned with the effect of its domain-matrix size and purity. These features, which are affected by factors such as block size, mold surface, and general fabrication procedures, as well as chemical structure, must be controlled if one is to have reproducible results in the function of an implant.

A study of molecular fractionation during the crystallization of polymers

Abstract: Polyethylenes of six different molecular weights and distributions have been crystallized isothermally from the melt at 90 to 129 °C and under elevated pressure (5,000 bar) at 225 to 240 °C. The crystallized polymer and the supernatant melt have been analyzed after quenching to low temperature, by selective dissolution using DSC and viscometry. In addition, data on solution crystallization of the literature were analysed. It was observed that fractionation occurs according to molecular weight. Melt and solution data on the critical molecular weight, chosen so that 90% by weight of the supernatant melt or solution has lower molecular weight and 90% of the crystals have higher molecular weight, agree when shifting the crystallization temperatures by 36 °C. The critical molecular weight-crystallization temperature relationship shows a 1/ΔT2 dependence. The equilibrium segregation on crystallization to hypothetical fully extended chain crystals yields a lower limit of segregation. At low supercooling, molecular lengths many times the equilibrium length and many times the lamellar thickness are reproducibly, selectively and permanently excluded from the crystal. Molecular nucleation is proposed to be the explanation for the observed facts.

Cross-linked water-swellable polymer particles

Abstract: Cross-linked water-swellable polymers are described, having a particle size of less than 4 microns. They are used as thickening agents for aqueous dispersions or solutions, particularly useful where high shear conditions are encountered in the application.

Process for cocrosslinking water soluble polymers and products thereof

Abstract: Poly(ethylene oxide) and at least one other water soluble polymer are conveniently cocrosslinked by exposing aqueous systems of the polymers to high energy irradiation. The resulting products are insoluble hydrophilic gels which can contain or when dried absorb large quantities of aqueous fluids and hence are useful as absorbing media for disposable absorbent articles, agricultural applications and the like.

Thermoplastic urethane elastomers. II. Effects of variations in hard-segment concentration

Abstract: The dynamic mechanical properties of thermoplastic urethane elastomers have been charac-terized for polymers composed of varying hard-segment concentrations and for two different molecular weight polyester diols as soft segments. The urethane polymers based on an 830 Mn polycaprolactone diol exhibited a progressive increase in glass transition temperature at increased levels of hard segments. In contrast, a similar series of polymers prepared with a 2100 Mn polycaprolactone diol as the soft segment maintained a relatively constant glass transition temperature. These differences are attributed to the relative degree of phase separation between the constitutive blocks of the copolymer. The polymers of both series possessed two lower-temperature, secondary relaxations, which are ascribed to methylene sequence mobility within the polycaprolactone units and to possible disruption of interfacial associations between the hard- and soft-segment structures.

Rate‐determining factors for enthalpy relaxation of glassy polymers. Molecular weight

Abstract: In order to obtain information concerning the effect of molecular weight on the molecular mobility involved in the relaxation processes associated with the nonequilibrium thermodynamic state of glassy polymers, enthalpy‐relaxation studies have been undertaken on glassy atactic polystyrenes of various molecular weights, ranging from 2.0×103 to 811×103. As was found in previous studies of enthalpy relaxation in organic glasses, the glass transition temperature Tg is the principal rate‐determining factor. From a more detailed analysis of the data, however, it is evident that the relaxation processes at corresponding temperature intervals below Tg are a function of the molecular weight. The relaxation rate decreases somewhat with increasing molecular weight and approaches a limiting value at molecular weights in the vicinity of 50×103, the critical molecular‐weight range in the molecular‐weight dependence of glass transformation. For Aroclor 5460, a nonpolymeric material of lower molecular weight but having a...

Process for grafting polymers on carbon black through free radical mechanism

Abstract: A process for grafting polymers on carbon black through a free radical mechanism comprising contacting of the black with the polymer and a thermal treatment. After formation of the carbon black mixture with at least one polymer, said mixture is degassed under vacuum at approximately room temperature, at least one substance acting as a solvent for said polymer is then introduced on said degassed mixture which is under vacuum, so as to form a solution of the latter containing the carbon black, said solution is heated with stirring at least at 50° C until a carbon black bearing polymer grafts is obtained and the latter can, if desired, be separated by filtration or centrifugation of the unattached polymer solution. The carbon black products bearing polymer grafts as well as this carbon black itself are easily dispersed in solvents. They find valuable applications in paints, varnishes, printing inks, among others. The increase in dispersibility of the grafted carbon black improves its efficiency as a pigment, ultraviolet screening agent, filler, antioxidant, and the like.

Process for preparing emulsions by polymerization of aqueous monomer-polymer dispersions

Abstract: Process for the preparation of aqueous homogeneous polymer emulsion which comprises mixing, generally with agitation or under shear conditions, water, surfactant, at least one polymer, e.g., cellulosic compounds, and at least one monomer, e.g., acrylics, methacrylics, styrene, etc., the polymer being soluble in said monomer, to form a dispersion of polymer-monomer particles in water; then subjecting said dispersion to conditions such that the monomer within the particles become polymerized by free radical polymerization thereby forming a substantially homogeneous blend of at least two polymers within the particles of the emulsion. The particles have on the average a diameter of 5 microns or less.

Production of p-phenylene sulfide polymers

Abstract: A method is provided for producing a p-phenylene sulfide polymer by contacting at least one p-dihalobenzene, at least one alkali metal sulfide, at least one alkali metal carboxylate, at least one organic amide and at least one alkali metal hydroxide to form a composition at polymerization conditions. The use of an alkali metal hydroxide in addition to the other compounds used in the reaction mixture results in p-phenylene sulfide polymers of higher molecular weight than produced without the alkali metal hydroxide, as evidenced by lower melt flow of the polymer than produced by the compared methods.

Polyurethane—polystyrene interpenetrating polymer networks

Abstract: Two component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks), composed of a polystyrene network (crosslinked with divinyl benzene) and a polyester-polyurethane network (crosslinked with trimethylolpropane), were made. Electron microscopy and glass-transition measurements showed that phase separation had resulted with some interpenetration, presumably occurring at the boundaries. At a composition of about 75 percent polyurethane, a phase inversion occurred, the continuous phase being polystyrene at polyurethane compositions of less than 75 percent. The stress-strain properties and hardness measurements agreed with these results. Enhanced tensile strength was observed in the IPN's in a concentration range where modulus reinforcement was not evident. A small enhancement in tear strength and thermal stability was also noted.