Showing papers on "Polymer blend published in 1994"

Interpenetrating Polymer Networks

Abstract: Interpenetrating polymer networks (IPN’s) are a unique type of polyblend, synthesized by swelling a crosslinked polymer (I) with a second monomer (II), together with crosslinking and activating agents, and polymerizing monomer II in situ (Sperling, 1974–1975 ; Sperling and Friedman, 1969). The term IPN was adopted because, in the limiting case of high compatibility between crosslinked polymers I and II, both networks could be visualized as being interpenetrating and continuous throughout the entire macroscopic sample.* As with other types of polyblends, if components I and II consist of chemically distinct polymers, incompatibility and some degree of phase separation usually result (Sperling, 1974–1975; Sperling and Friedman, 1969; Sperling et al., 1970a,b,c; 1971). Even under these conditions, the two components remain intimately mixed, the phase domain dimensions being on the order of hundreds of angstroms. If one polymer is elastomeric and one polymer is plastic at the use temperature, the combination tends to behave synergistically, and either reinforced rubber or impact-resistant plastics result, depending upon which phase predominates (Curtius et al., 1972; Sperling and Mihalakis, 1973; Sperling et al., 1971; Huelck et al., 1972). Among the other kinds of polymer blends discussed in this monograph, the graft-type copolymers are the ones most closely related to the IPN’s.

Selective localization of carbon black in immiscible polymer blends: A useful tool to design electrical conductive composites

Abstract: It is shown how efficiently the percolation threshold of carbon black in polyethylene/polystyrene heterogeneous blends can be decreased by selective localization of CB particle at the interphase rather than in one phase of the blend

Double-walled polymer microspheres for controlled drug release

Abstract: One approach to the controlled release of drugs involves incorporation of the drug molecules into the matrix of microscopic polymer spheres or capsules. Existing methods for preparing such microparticles do not, however, always guarantee a constant release rate, for example because drug molecules may be trapped preferentially at the surface, because they have to diffuse through an increasing thickness of polymer when the particles are non-eroding or because the surface area changes for eroding particles. In other situations pulsed release may be required--an application to which simple polymer microspheres do not readily lend themselves. Multi-walled microspheres might solve some of these problems. Here we describe a one-step process for preparing double-walled polymer microspheres with diameters ranging from about 20 to 1,000 micrometers. Our technique involves the phase separation of a polymer mixture owing to solvent evaporation: with an appropriate choice of interfacial tensions and evaporation rate, a spherical droplet of one polymer becomes coated with a highly uniform layer of the other. This process, which might be adapted to yield multi-walled microspheres, should make possible the engineering of highly specific drug-release properties.

PRISM theory of the structure, thermodynamics, and phase transitions of polymer liquids and alloys

Abstract: The recent development of a microscopic theory of the equilibrium properties of polymer solutions, melts and alloys based on off-lattice Polymer Reference Interaction Site Model (PRISM) integral equation methods is reviewed. Analytical and numerical predictions for the intermolecular structure and collective density scattering patterns of both coarse-grained and atomistic models of polymer melts are presented and found to be in good agreement with large scale computer simulations and diffraction measurements. The general issues and difficulties involved in the use of the structural information to compute thermodynamic properties are reviewed. Detailed application of a hybrid PRISM approach to calculate the equation-of-state of hydrocarbon fluids is presented and found to reproduce accurately experimental PVT data on polyethylene. The development of a first principles off-lattice theory of polymer crystallization based on a novel generalization of modern thermodynamic density functional methods is discussed. Numerical calculations for polyethylene and polytetrafluoroethylene are in good agreement with the experimental melting temperatures and liquid freezing densities. Generalization of the PRISM approach to treat phase separating polymer blends is also discussed in depth. The general role of compressibility effects in determining small angle scattering patterns, the effective chi-parameter, and spinodal instability curves are presented. New theoretical concepts and closure approximations have been developed in order to describe correctly long wavelength concentration fluctuations in macromolecular alloys. Detailed numerical and analytical applications of the PRISM theory to model athermal and symmetric blends are presented, and the role of nonmean field fluctuation processes are established. Good agreement between the theory and computer simulations of simple symmetric polymer blends has been demonstrated. Strong, nonadditive compressibility effects are found for structurally and/or interaction asymmetric blends which have significant implications for controlling miscibility in polymer alloys. Recent generalizations of PRISM theory to treat block copolymer melts, and nonideal conformational perturbations, are briefly described. The paper concludes with a brief summary of ongoing work and fertile directions for future research.

Component Dynamics Miscible Polymer Blends: A Two-Dimensional Deuteron NMR Investigation

Abstract: The dynamics of individual components in 1,4-polyisoprene/poly(vinylethylene) miscible blends are studied using two-dimensional deuteron exchange NMR. The rate of the backbone reorientation process near the glass transition is quantitatively determined for each species in a miscible blend as a function of temperature. We demonstrate that the broad glass transition arises both from a wide distribution of segmental motional rates for each species and from intrinsic differences in the motional rate between the two species. In addition, the temperature dependence of their motional rates in the blend DSC glass transition region suggests that the two components undergo distinct effective glass transitions, which is consistent with previously observed thermorheologically complex behavior. The origins of dynamic heterogeneity are examined further by comparing the experimental results with a simple model calculation that takes into account the effect of composition variations in an ideal miscible blend. This comparison suggests that the observed dynamic heterogeneities can be explained only by including two distinct contributions: local composition variations in the blend and intrinsic differences in chain mobilities.

Observation of the Component Dynamics in a Miscible Polymer Blend by Dielectric and Mechanical Spectroscopies

Abstract: Dielectric and mechanical relaxation measurementa of the local segmental relaxation in miscible blends of poly(vinylethy1ene) (PVE) and polyisoprene (PIP) have been made under isothermal conditions over a wide range of frequency. Taking advantage of the prominence of respectively the PVE contribution to dielectric relaxation and the PIP contribution to mechanical relaxation, we are able to resolve the dynamics of each component in some of the blends. From the observed dynamics of individual componenta, we establish as experimental facta that the most probable local segmental relaxation time of each component haa a different magnitude as well as different temperature dependence. Moreover, the relaxation spectrum of each component broadens as temperature is decreased. Thus a breakdown of thermorheological simplicity occurs not only in the dynamics of each component but a fortiori when the contributions from both Components are considered together. The degree to which these effecta manifest themselves depends on the blend composition. All these experimental features are shown to be in accord with a theory of segmental dynamics for blends that is obtained as ageneralization of the coupling model for homopolymers by taking into account local concentration fluctuations.

Polymerization in supercritical fluid-swollen polymers : a new route to polymer blends

Abstract: This paper describes the infusion of CO 2 solutions of styrene into a variety of semicrystalline and amorphous polymers (polychlorotrifluoroethylene, poly(4-methyl-1-pentene), HDPE, nylon 66, polyoxymethylene and Bisphenol A polycarbonate) and thermally radical polymerizations within the swollen substrates to generate polystyrene-substrate polymer blends

Fabricated articles made from ethylene polymer blends

Abstract: The disclosed ethylene polymer compositions have et least one homogeneously branched substantially linear ethylene/α-olefin interpolymer and at least one heterogeneously branched ethylene polymer. The homogeneously branched linear or substantially linear ethylene/α-olefin interpolymer has a density from about 0.88 to about 0.935 g/cm3 and a slope of strain hardening coefficient greater than or equal to about 1.3. Films made from such formulated compositions have surprisingly good impact and tensile properties, and have an especially good combination of modulus and toughness.

Counter-ion induced processibility of polyaniline: conducting melt-processible polymer blends

Abstract: Summary form only given. Conducting polymer blends made by blending thermoplastic bulk polymers with Polarene/sup TM/, a proprietary conducting polyaniline composition, using conventional melt-processing techniques are reported. The percolation threshold for conductivity is observed at astonishingly low weight fractions of the conjugated conducting polyaniline indicating the formation of a unique morphology. Results on electrical and mechanical properties of these blends will be presented and discussed.

Characterization of Hydrogen Bonding in Cellulose-Synthetic Polymer Blend Systems with Regioselectively Substituted Methylcellulose

Abstract: Specifically substituted O-methylcelluloaea, 2,3-di-O-methylcellulose and 6-O-methylcelluloae were used as cellulosic components in blends with poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA). Since their hydroxyl groups (OH) form controlled intra- and intermolecular hydrogen bonds, the cellulose derivatives are useful as model compounds to investigate the effect of hydrogen bonding in cellulose-synthetic polymer blend systems. FTIR spectra of the cellulosic-PEO blend films revealed that, while the primary hydroxyl groups at the C-6 position of cellulose interact strongly with ether oxygen in PEO, the secondary hydroxyl groups at the C-2 and C-3 positions show no evidence for polymer-polymer interactions

Compositional Dependence of Segmental Dynamics in a Miscible Polymer Blend

Abstract: The segmental motion of each species in polyisoprene/poly(vinylethylene) (PI/PVE) miscible blends is studied at three different compositions using two-dimensional deuteron exchange NMR (2D ^2H NMR). The individual species exhibit widely different mean mobilities and broad mobility distributions near the glass transition of each blend. As the PVE content increases, both the difference in mean mobilities between the two species and the width of the mobility distribution for both components increase. The change in these two types of dynamic heterogeneity with PVE content appears to produce the anomalous broadening of the glass transition. The mean reorientational correlation times of each component can differ by 2 orders of magnitude under identical conditions. This difference can be described in terms of distinct effective glass transition temperatures, T_g*, for the two species. The separation between the two effective glass transition temperatures increases almost monotonically with PVE content, consistent with the more pronounced thermorheological complexity of blends rich in PVE. The individual T_g*'s also exhibit a different compositional dependence from that of the calorimetric T_g of the blend observed by differential scanning calorimetry (DSC). This behavior can give rise to the complex compositional dependence of individual mobilities, apparent when the mobilities are compared at the same T - T_g with respect to the DSC T_g of the blend.

Acid‐ and alkali‐catalyzed tannin‐based rigid foams

Abstract: Acid- and alkali-catalyzed polyflavonoid tannin-based rigid foams were prepared. These foams have comparable physical and mechanical properties to the synthetic phenolic rigid foam used as a comparative standard. The fluid polymer phase was based on a mimosa tannin-formaldehyde resin with a minor addition of a fortifier resin. Expansion of the fluid phase was brought about by a physical blowing agent, whereas dimensional stabilization was achieved through cross-linking at the desired density. In the case of the acid-catalyzed foam, a heat-generating agent in the form of furfuryl alcohol was employed. The polymer composition of tannin–formaldehyde/urea–formaldehyde systems as a function of pH was predicted from the respective gel times and rate constants, i.e., above pH 7, the copolymer proportion will tend to 100% and, that at pH 3.4, the polymer blend proportion will tend to a maximum. © 1994 John Wiley & Sons, Inc.

Homogeneous nucleation of the dispersed crystallisable component of immiscible polymer blends

Abstract: Immiscible melt mixed blends of a crystallisable polyolefin (isotactic polypropylene, PP) and atactic polystyrene (PS) were prepared in a wide composition range. It was found that when PP is the major component in the blend its crystallisation behaviour is not affected by blending it with PS. However if PP is the minor component, it will be dispersed in the immiscible PS matrix, hence the nucleation mechanism changes from predominantly heterogeneous to predominantly homogeneous as long as the size of the dispersed PP droplets is below a critical value (of the order of 1–2 μm).

Blends of glycolide and/or lactide polymers and caprolactone and/or trimethylene carbonate polymers and absorbable surgical devices made therefrom

Abstract: Polymer blends of glycolide and/or lactide homopolymer and/or glycolide/lactide copolymer and polycaprolactone and/or polytrimethylene carbonate homopolymer or copolymers thereof and absorbable surgical devices manufactured therefrom having improved mechanical properties, such as improved impact resistance and improved cyclic flex, are disclosed.

heat sealable films and articles made therefrom.

Abstract: Heat sealed articles and heat sealable films comprising a polymer blend of a first polymer having a narrow molecular weight and composition distribution and a second polymer having a broad molecular weight distribution and composition distribution. The articles and films have significantly improved physical characteristics and remarkably low heat seal initiation temperatures, high seal strength, high hot tack and therefore provide improved processibility and higher line speeds on commercial heat sealing equipment.

Microphases and macrophases in polymer blends with a diblock copolymer

Abstract: Blends A/αβ and C/αβ of a polymer A or C and a diblock copolymer αβ with blocks α and β of equal lengths were analysed, where A is chemically equal to α while C has attactive interactions with α. Films of the blends were cast, using nonselective solvents. The random phase approximation model predicts a transition from microscale to macroscale fluctuations in the still homogeneous solutions, the transition depending on the chain lengths of A or C, relative to that of αβ, on the interactions, in particular those of C and α, and on the temperature. This transition was observed, where predicted, in cast films of various blends of a diblock copolymer P(MMA-b-S) of methyl methacrylate and styrene

Compositional heterogeneities in hydrogen-bonded polymer blends: infrared spectroscopic results

Abstract: The equilibrium constants describing phenolic OH/ester carbonyl hydrogen bonds are experimentally determined for polymer blends, mixtures of low molecular weight analogues of the polymer repeat units, solutions of the polymers in the low molecular weight analogues, and random copolymers of the original blend segments. These equilibrium constants are determined by IR spectroscopy, and it is demonstrated that the interactions in the low molecular weight analogues and polymer solutions are (within error) described by the same equilibrium constant. The blend equilibrium constant has a value that is much smaller (about 25% of the solution value), while the copolymer value is intermediate between these two extremes

Surface properties for poly(perfluoroalkylethyl methacrylate)/poly(n-alkyl methacrylate)s mixtures

Abstract: A poly(perfluoroalkylethyl methacrylate) and a series of poly(n-alkyl methacrylate)s such as poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n-butyl methacrylate) were prepared and used to investigate the surface properties of polymer mixtures containing a fluorinated homopolymer and a nonfluorinated homopolymer and the effect of the side-chain length of poly(n-alkyl methacrylate) on the surface free energy for the polymer mixtures. Contact angles were measured for the surfaces of polymer mixtures by varying the concentration of poly(perfluoroalkylethyl methacrylate). From the contact angle data, it can be inferred that most of the poly(perfluoroalkylethyl methacrylate) added to poly(n-alkyl methacrylate)s is located in the outermost layer of polymer-mixture surface. Surface free energies for the outermost surfaces of polymer mixtures were calculated from the contact angle data using Owen and Wendt's equation. The decrease in the surface free energy for the polymer mixture with the poly(perfluoroalkylethyl methacrylate) addition is more pronounced as the side-chain length of poly(n-alkyl methacrylate) decreases. Due to the steric effect of the side chain of poly(n-alkyl methacrylate), the arrangement of the perfluoroalkylethyl group of poly(perfluoroalkylethyl methacrylate) to the air side is considerably hindered. The ESCA analysis of atomic compositions of the surface for the polymer mixture verified that poly(perfluoroalkylethyl methacrylate) is preferentially arranged and concentrates at the polymer mixture–air interface. The results of functional group compositions obtained by ESCA showed that the functional group composition of CF3 for the outermost layer has a more important effect on the surface free energy than that of CF2 and confirmed the hindrance of the arrangement of perfluoroalkylethyl group to the air side by the side chain of poly(n-alkyl methacrylate). © 1994 John Wiley & Sons, Inc.

Model experiments for the interfacial reaction between polymers during reactive polymer blending

Abstract: Bilayer film Fourier transform infrared (FTIR) model experiments are designed to provide a well-defined interface for study which can be probed by infrared spectroscopy during the interdiffusion and reaction of two reactive polymers. This provides a model experiment to determine the kinetics and extent of reaction between functionalized polymers during reactive polymer blending. This type of experiment provides data on the reaction at a stagnant interface which is necessary for the analysis of the interface while it is simultaneously undergoing deformation. It is also useful as a screening or preliminary experiment on reactive blending systems in that the extent of reaction may be followed for different systems at different temperatures. Experiments reported here trace the reaction of a styrene–maleic anhydride copolymer with two different amine terminated polymers. Results are obtained for the interdiffusion and reaction of a styrene-maleic anhydride copolymer with two amine terminated polymers: a butadiene-acrylonitrile copolymer and Nylon 11. The kinetics from these experiments include contributions due to both interdiffusion and chemical reaction. The chemical reaction kinetics may be isolated from the diffusion kinetics by performing experiments on well-mixed systems which are prepared by casting films of the polymer mixtures from a mutual solvent. © 1994 John Wiley & Sons, Inc.

Polypropylene-graft-Polycaprolactone: Synthesis and Applications in Polymer Blends

Abstract: A new graft copolymer, polypropylene-graft-polycaprolactone (PP-g-PCL), is prepared which is an effective compatibilizer for PP blends with many engineering plastics, such as polycarbonate (PC) and PVC. The chemistry in the preparation of this graft copolymer involves hydroxylated PP, containing primary or secondary alcohol groups, and the anionic ring opening polymerization of e-caprolactone (e-CL). Despite the heterogeneous reaction conditions, the molecular structures of PP-g-PCL copolymers can be controlled by OH content, e-CL concentration, and reaction time. In the bulk, the indivdual PP and PCL segments in the graft capolymers are crystallized into two separate phases with high crystallinities

Miscibility and interaction studies on some aqueous polymer blend solutions by ultrasonic and rheological techniques

Abstract: The aqueous solutions of poly(ethylene oxide)–polyacrylic acid, poly(vinyl pyrrolidone)–poly(vinyl alcohol), and poly(ethylene oxide)–poly(vinyl alcohol) blends have been studied by ultrasonic, rheological, and viscometric techniques. Extensive investigation over a wide range of concentrations, temperatures, compositions, pH, and shear rates indicate the degree of miscibility, extent of interaction between the polymers, and stoichiometry of the polymer complexes formed by the strong interaction between the polymers in solutions. These investigations indicate the miscibility of poly(ethylene oxide)–polyacrylic acid and poly(ethylene oxide)–poly(vinyl pyrrolidone) blends and the immiscibility of poly(ethylene oxide)–poly(vinyl alcohol) blends in conformity with other reported investigations. © 1994 John Wiley & Sons, Inc.

Surface segregation in polymer blends due to stiffness disparity

Abstract: The entropy‐driven surface segregation of polymer blends is investigated via computer simulations and integral equation theory. The model system is composed of a binary blend at a hard wall where one of the components of the blend is stiffer than the other. It is found that, at meltlike densities relevant to experiments, both simulations and microscopic theory predict the segments of the stiffer chains segregate to the surface.