Showing papers on "Polymer published in 1976"

Polymers at Interfaces and the Interactions in Colloidal Dispersions

Abstract: Solutions of different polymers in the same solvent are incompatible as a rule and show phase separation when they are mixed. If incompatibility is also to be observed in systems where one of the polymer components is replaced by colloidal particles, sterically stabilized by a cover of polymer chains, will be discussed in this lecture. After a discussion of the applicability of statistical thermodynamical criteria for colloid stability we focus attention on the potential of average force between two particles, V(r), and the second virial coefficient, B2. First it is shown from general arguments that V(r) and B2 always decrease in magnitude upon addition of particles identical to the particle pair considered. The decrease is particularly large for high molecular weight polymers. Subsequently, the analysis is extended, with the help of simple models, to mixtures of polymer colloid and polymer. It is predicted that B2 should decrease and may become negative when the molecular weight and concentration of the polymer are sufficiently large. For high molecular weight polymer this is of the order of a per cent or less. More polymer is needed for low molecular weights. The destabilization is intimately connected with the expulsion of polymer from the interstitial spaces between approaching particles because of “volume restriction”- and “osmotic” effects. The predictions are in accordance with some experiments that were available. Finally the applicability of light scattering as an experimental tool in these stability problems is stressed. Results are also given of the incompatibility of two polymers in a single solvent in which one of the polymers is masked i.e. does not scatter light.

A new derivation of average molecular weights of nonlinear polymers.

Abstract: A new method for calculating average molecular weights is presented for nonlinear polymers. In contrast to the previous methods of Flory and Stockmayer which first calculate the distribution of all species and then use the distributions to calculate average properties, the new method calculates these properties directly. In contrast to the method of Gordon, probability generating functions are not required. Starting with elementary probability and utilizing the recursive nature of network polymers property relations can be developed more simply. We illustrate the method for calculations of Mw Mz, and the gel point for a wide variety of polyfunctional polymerizations.

Liquid crystal polymers. I. Preparation and properties of p-hydroxybenzoic acid copolyesters†

Abstract: High molecular weight copolyesters were prepared by the acidolysis of poly(ethylene terephthalate) with p-acetoxybenzoic acid and polycondensation through the acetate and carboxyl groups. The mechanical properties of the injection-molded copolyesters containing 40–90 mole-% p-hydroxybenzoic acid (PHB) were highly anisotropic and dependent upon the PHB content, polyester molecular weight, injection-molding temperature, and specimen thickness. As the injection-molding temperature increased and the specimen thickness decreased, the tensile strength, stiffness, and Izod impact strength increased when measured along the direction of flow of the polymer melt, and the coefficient of thermal expansion was zero. In some compositions these properties were superior to those of commercial glass fiber reinforced polyesters. Maximum tensile strengths, flexural moduli, notched Izod impact strengths, and minimum melt viscosities were obtained with polyesters containing 60–70 mole-% PHB. Higher oxygen indicies (39–40) and heat deflection temperatures (150–220°C) were obtained with 80–90 mole-% PHB.

Small-angle x-ray and light scattering studies of the morphology of blends of poly(ϵ-caprolactone) with poly(vinyl chloride)†

Abstract: Solvent-cast films of blends of poly(ϵ-caprolactone) (PCL) with poly(vinyl chloride) (PVC) were examined by low-angle x-ray scattering and by small-angle light scattering. X-ray scattering from crystalline compositions were analyzed using the Tsvankin–Buchanan technique and led to values of the repeat period of the lamellar structure and the thickness of the crystalline and amorphous layers. With increasing content of PVC, the amorphous layer thickness increased sufficiently to accommodate the PVC, leading to values of the linear crystallinity consistent with macroscopic measurements by density and DSC techniques up to about 50% PVC by weight. Above this concentration, the lamellar structure no longer appeared to be volume filling. At high concentration of PCL, the polymer consisted of volume-filling spherulites containing the lamellar substructure. Spherulite sizes were measured by light scattering and absolute light scattering intensities were consistent with calculations based upon the degree of crystallinity and anisotropy of the spherulites. Compositions containing more than 60% PVC were amorphous. Low-angle x-ray scattering was interpreted in terms of the Debye–Bueche theory which leads to values for a correlation distance lc and the mean-square electron density fluctuation 〈η2〉 (which was also obtained from the invariant). By the method of Porod, the correlation distances were resolved into persistence lengths within the two phases, which were determined as a function of composition. The fluctuation 〈η2〉 was analyzed in terms of a two-phase model to show that its value was somewhat larger than would be obtained if the phases were composed of the pure components. It was not possible to uniquely determine their compositions. The data were consistent with the existence of a transition zone of the order of 30 A thick between phases.

Kinetics and Mechanism of Emulsion Polymerization

Abstract: The course of emulsion polymerization may be considered as involving three intervals: Interval I, where particle formation takes place. The end of this interval is not dependent upon the degree of conversion, but on the total amount of polymer formed. With usual recipes, it ends at about 1-5% conversion. Interval II lasts from the end of Interval I until monomer disappears as a separate phase. In this interval, the particle number is usually found to be constant, the particle volume increases proportional to conversion, the monomer concentration in the particles is approximately constant, and therefore the termination is also constant within the particles. Interval III starts when the monomer disappears as a separate phase. The transition from Intervals II to III is determined by the degree of conversion and differs for different monomers. In cases where the solubility of monomer in the water phase is low, the monomer present in the aqueous phase may usually be neglected compared to the monomer p...

Process for preparing polyolefins

Abstract: According to the present invention, in a vapor phase polymerization of olefins, there is provided an efficient polyolefin manufacturing process capable of preventing the formation of a sheet-like polymer and allowing an olefin polymerization reaction to be started stably. More particularly, there is provided a process of preparing a polyolefin by homopolymerizing or copolymerizing an olefin or olefins substantially in a vapor phase condition and in the presence of a catalyst comprising a solid catalyst component and an organometallic compound, the solid catalyst component containing magnesium, one or more elements selected from titanium and vanadium and also containing halogen, wherein, in feeding the catalyst into a reactor the interior of which is held substantially in a vapor phase condition, in the presence of a polyolefin serving as a medium for dispersing the catalyst and in a state not substantially inducing a polymerization reaction in the presence of only the said polyolefin serving as the said medium, to start homopolymerization or copolymerization of the olefin(s), a solid catalyst component satisfying the above condition and having an average particle diameter substantially larger than that of the solid catalyst component to be used in a principal stage of the polymerization reaction is used at least until an olefin homopolymer or copolymer is formed in an amount equal to the amount of the polyolefin used as the catalyst dispersing medium.

Plasma for Modification of Polymers

Abstract: The effect of nonpolymer-forming plasma (e.g., plasma of hydrogen, helium, argon, nitrogen) can be viewed as the following two reactions: 1) reaction of active species with polymer, and 2) formation of free radicals in polymer which is mainly due to the UV emitted by the plasma. The incorporation of nitrogen into the polymer surface by N2 plasma and the surface oxidation by O2 plasma are typical examples of the first effect. The latter effect generally leads to incorporation of oxygen in the form of carbonyl and hydroxyl and to some degree of cross-linking depending on the type of substrate; however, the degradation of polymer at the surface manifested by weight loss occurs in nearly all cases when polymers are exposed to plasma for a prolonged period of time. The effects of polymer-forming plasma is predominated by the deposition of polymer (plasma polymer); however, with some plasma-susceptible polymer substrates the effect of UV emission from polymer-forming plasma cannot be neglected. The mec...

The drawing behavior of linear polyethylene. I. Rate of drawing as a function of polymer molecular weight and initial thermal treatment

Abstract: The drawing behavior of a series of linear polyethylene homopolymers with weight-average molecular weight (Mw) ranging from 67,800 to ∼3,500,000 and variable distribution (Mw/Mn = 5.1−20.9) has been studied. Sheets were prepared by two distinct routes: either by quenching the molten polymer into cold water or by slow cooling below the crystallization temperature (∼120°C) followed by quenching into cold water. When the samples (2 cm long) were drawn in air at 75°C using a crosshead speed of 10 cm/min it was found that for low Mw polymers the initial thermal treatment has a dramatic effect on the rate at which the local deformation proceeds in the necked region. At high Mw such effects are negligible. An important result was that comparatively high draw ratios (λ > 17) and correspondingly high Young's moduli could be obtained for a polymer with Mw as high as 312,000. It is shown how some of the structural features of the initial materials (mainly studied by optical microscopy, small-angle x-ray scattering and low-frequency laser Raman spectroscopy) can be interpreted in terms of the molecular weight and molecular weight distribution of the polymers. Although crystallization and morphology can be important at low Mw, it suggested that the concept of a molecular network which embraces both crystalline and noncrystalline material is more helpful in understanding the drawing behavior over the whole range of molecular weights.

A non-linear viscoelastic model with structure-dependent relaxation times: I. Basic formulation

Abstract: A non-linear constitutive equation for polymer melts and concentrated solutions is presented. Based on known results of network theories, the model contains a distinctive feature: that of letting the relaxation times depend upon the existing structure. The model extends the constitutive equation of linear viscoelasticity to the non-linear region in a well-defined way, with the uncertainty of just a single adjustable parameter. Predictions of the model for common cases of non-linear response are derived and discussed.

High‐conversion polymerization. I. Theory and application to methyl methacrylate

Abstract: The concept of polymer entanglements has been applied in conjunction with classical free-radical kinetics to describe vinyl polymerizations carried to high conversion A kinetic model has been developed on the assumption that two populations of radicals exist in a high-conversion polymerization system: those radicals whose chain lengths are long enough to become entangled with neighboring molecules and have, therefore, a restricted mobility; and those shorter radicals whose mobilities are not strongly affected by diffusional effects It has also been assumed that the kinetic rate constant for the termination step between entangled radicals is inversely proportional to the mean entanglement density The model contains only two parameters in addition to the kinetic rate constants required to describe low-conversion polymerizations One of these parameters can be determined, at least in principle, from measurements of solution properties of the polymer-monomer mixtures The model so developed has been tested against experimental data obtained from the literature on the bulk polymerization of methyl methacrylate The agreement between predicted and experimental monomer conversions and molecular weight averages is found to be satisfactory

Synthesis and structure of the p-hydroxybenzoic acid polymer

Abstract: The synthesis and structure of the p-hydroxybenzoic acid polymer is described. The polymer was successfully prepared from either the phenyl ester of p-hydroxybenzoic acid or from p-acetoxybenzoic acid. With highly purified acetoxybenzoic acid, single crystals of the polymer could be prepared. The structure of the polymer was determined and shown to consist of a double helix where the two chains are in a reversed head-to-tail order. The unit cell dimensions are: a = 17.8 A and c = 18.4 A, where c corresponds to the chain length with a repeat distance of three units. The mechanism of polymerization and formation of the single crystal is discussed. The polymer displays a reversible high-temperature crystalline transition at 325–360°C (not a melting point). The transition was characterized by differential thermal analysis, differential calorimetry, thermal expansion coefficient measurements, high-temperature x-ray scans, and dielectric constant determinations. Orientation of the polymer chains during fabrication and changes in the mechanism of oxidative degradation above the crystal transition are described.

Polyimide structure-property relationships. II - Polymers from isomeric diamines

Abstract: An extensive study of the effects of stereoisomeric variations in aromatic polyimide structures on polyimide properties was conducted. The structural variations were incorporated into the polyimides through the use of two complete series of isomeric aromatic diamine monomers, the diaminodiphenylmethanes and the diaminobenzophenones, as well as several pairs of diamine isomers. The ability of the diamines to polymerize was related to the basicities, and thus reactivities, of the amino groups. Diamines with an amino group located ortho to the group connecting the two aromatic rings were successfully polymerized with dianhydrides for the first time to high molecular weight poly(amic acids). The stereoisomeric polyimides were characterized by determining the glass transition temperatures Tg, mechanical properties, and thermooxidative stabilities of thin films of the polymers. The polymers prepared from p-diamines were shown to have the highest softening points and thus, the most rigid molecular structures. Those synthesized from m-diamines had the lowest Tg values, inferring the most flexible molecular backbone. With limited exceptions, the use of diamines with ortho-oriented amine groups failed to improve the flexibility of the polyimides since their Tg values were usually as high as those of polymers made from p-diamines. Only slight differences in mechanical properties of the isomeric polyimide films were attributable to the variations in isomeric structure, except for those properties dependent upon Tg changes, such as elevated temperature mechanical properties. A study of the thermooxidative stability of the polyimides showed little difference between the polymers prepared from the diaminobenzophenones, but marked differences were observed between the individual members of the diaminodiphenylmethane-derived polyimides.

Method for curing polymers containing one or more carboxy or anhydride functions and compositions

Abstract: β-HYDROXYALKYLAMIDES AND CERTAIN POLYMERS THEREOF ARE DISCLOSED AS CURING AGENTS FOR POLYMERS CONTAINING ONE OR MORE CARBOXY OR ANHYDRIDE FUNCTIONS. Also, self-curing copolymers containing carboxy and β-hydroxyalkylamide functionality are disclosed. The β-hydroxyalkylamides are either known compounds or may be prepared by treating an ester with an appropriately substituted amine. The β-hydroxyalkylamides are effective in solution, aqueous emulsion and powder coating formulations.

Pressure sintering of Si3N4

Abstract: The sintering of Si3N4 with 5% MgO was investigated at 1450 to 1900‡ C under a pressure of nitrogen. A maximum density of 95% of the theoretical value was obtained, which is greater than that obtained by pressureless sintering. The sintering process was inferred to be liquid-phase sintering and divided into two processes; rearrangement and solution-precipitation. The contribution of rearrangement to densification was about 10% in the present system, and the rest, up to 17% was due to solution-precipitation. Application of the present method of sintering Si3N4 with a high strength grain-boundary phase at high temperature is surveyed.

Adhesion aspects of metallization of organic polymer surfaces

Abstract: Organic polymer surfaces are metallized in two general ways: (i) thin film metallization in which metals are deposited by vapor deposition, sputtering, etc. and (ii) relatively thick metal coatings are deposited by means of electroless deposition followed by electrolytic deposition. In the present review paper, various applicable mechanisms—mechanical or interlocking, weak boundary layer, chemical, and electrostatic—of adhesion, relevant properties of metals and polymers, and techniques of controlling adhesion in metallized polymers are discussed, but the thin metallization of polymers has been emphasized. Evidence and mechanisms for the charge transfer across the metal–polymer interface are reviewed and the electrostatic component of adhesion is discussed. Apparently, there is a linear relationship between the charge transferred across the metal–polymer interface and the work‐function difference between the metal and the polymer. It is concluded that the electrostatic component of adhesion may have some ...

Comments on Exclusion of Polymer Chains from Small Pores and Its Relation to Gel Permeation Chromatography

Abstract: Some criticisms of our theoretical treatment of the partial exclusion of flexible-chain polymers in solution from cavities of macromolecular size and its application to gel permeation chromatography are examined. In other discussion, it is confirmed by simple reasoning that the identification, explicit or implicit in various studies, of the mean projection of a polymer molecule onto a line as a characteristic dimension governing the extent of permeation of simple pores does not depend on specific molecular models. Our previous calculation of permeation by certain random-flight branched-chain species is shown to lead, incidentally, to the mean projection for these structures. From relations between the mean projection and the hydrodynamic volume of a molecule, it appears that the product of intrinsic viscosity and molecular weight is not a common calibration factor for elution of all molecular species from a gel chromatographic column, but theory and experience do support the validity of this correlation among solutes with similar molecular architecture.

The use of polymer supports in organic synthesis. V. The preparation of monoacetates of symmetrical diols

Abstract: A 2% cross-linked divinylbenzene–styrene copolymer was directly lithiated with n-butyllithium in the presence of N,N,N′,N′-tetramethylethylenediamine The lithiated polymer on reaction with a benzophenone gave an insoluble polymer-bound trityl alcohol Further reaction with acetyl chloride gave a polymer-bound trityl chloride which, on treatment with the primary symmetrical diols 1,10-decanediol, 1,7-heptanediol, and 1,4-butanediol, gave mostly symmetrical diols monoblocked by insoluble polymer-bound trityl groups Acetylation followed by acid cleavage from the polymer gave the monoacetates of 1,10-decanediol, 1,7-heptanediol, and 1,4-butanediol and some recovered diols The recovered polymer can be efficiently recycled The quantity of recovered diol was related to the problem of 'double-binding' of the symmetrical diols to the polymer-bound trityl groups The extent of 'double-binding' could be greatly reduced by the use of polymer-bound trityl chloride prepared via the lithiated polymer and methyl benz

Blends of certain hydrogenated block copolymers

Abstract: Polymeric blends, covering the range from rubber-like to flexible mechanical behavior, having outstanding resistance to shrinkage and distortion on heat aging, resistance to ozone, good tensile properties, resilience, processability, as well as a combination of toughness and flexibility are comprised of certain selectively hydrogenated block copolymers and polyamide polymers.

Novel polytriazine compounds

Abstract: Novel tetraalkyl piperidine radical containing polytriazine compounds are produced by reacting a dihalogen-triazine with a bifunctional compound containing amine, alcohol, mercaptan or phenol groups at least one of the bifunctional compounds containing a tetraalkyl piperidine radical. The compounds are valuable light stabilizers for synthetic polymers, particularly polyolefin in the form of fibers or films.

The effect of cationic polymers on the colloidal stability of latex particles

Abstract: Using a simple turbidimetric procedure, relative flocculation rates of a polystyrene latex suspension with three cationic polymers and a cationic surfactant have been determined. All four materials showed about the same optimum flocculation concentration when expressed in equivalent amounts, indicating the predominance of charge effects. In agreement with previous findings, a considerable enhancement of flocculation rate was observed with cationic polymers of moderately high molecular weight, which is consistent with the “electrostatic patch” model of polyelectrolyte adsorption. At optimum polymer concentration, it was found that the rate of flocculation after a two-stage addition of suspension was just the same as that after the conventional one-stage addition. This, at first sight, surprising result also can be explained in terms of a simple patchwise adsorption model. However, the rate enhancement is considerably underestimated by this simple model, probably because the mutual orientation of colliding particles is not taken into account.

Process for the manufacture of crosslinked polymers which contain imide groups

Abstract: The invention relates to the manufacture of crosslinked polymers which contain imide groups by reacting polymaleimides with alkenylphenols or alkenylphenol ethers, preferably at temperatures of 100° to 250° C. The reaction mixture optionally also contains polymerization catalysts. The manufacture of the polymers is as a rule carried out with simultaneous shaping. Shaped articles (for example castings), laminates, adhesive bonds and foams can be manufactured in this way. It is also possible to carry out the reaction in solution.