Theoretical approach to the temperature dependence of local flow in polymer systems

Summary Starting with the concept of temperature dependent apparent activation energy of flow as a specific temperature function of the considered polymer system a general appraoch is presented, which includes both the Arrhenius and the WLF behaviour. It is demonstrated how local flow can be characterized directly from mechanical measurements via temperature dependent apparent activation energy of flow, using two parameters only, the apparent activation energy of flow extrapolated to infinite temperature, and the Vogel temperature as obtained by extrapolation to infinite activation energy.Examples are given in order to confirm the usefullness of these parameters for molecular interpretation of changes in the local flow mechanism as well as for clarification of the dependences between the polymer structure and the local flow process. As an unique effect it has been found that the energetic interaction of oligomeric polystyrene with poly(vinylmethylether) is much more pronounced than that with high molecular weight polystyrene. This findings may exhibit technical relevance.Herrn Prof. Dr. Dr. H. C. Mult. G. V. Schulz zu seinem 80. Geburtstag mit allen guten Wünschen gewidmet     

Physical aging in the mechanical properties of miscible polymer blends

Changes in mechanical properties during isothermal physical aging were investigated for three miscible blends: polystyrene (PS)/poly(2,6-dimethyl 1,4-phenylene oxide) (PPO), PS/poly(vinylmethylether) (PVME), and poly(methylmethacrylate) (PMMA)/poly(ethyleneoxide) (PEO). The kinetics of stress relaxation was investigated for the blend, dilute in one component, and compared with that of the neat major component at equal temperature distances, Tg-T, from the midpoint glass transition temperature. It is demonstrated that for all three blends, the mean stress relaxation time (τ) does not scale with Tg-T. For PS/PPO and PS/PVME blends, the stress relaxation rates are faster compared to neat PS; for PMMA/PEO, they are slower than for neat PMMA. Two effects appear to be important in contributing to this discrepancy. First, addition of the second component produces a change in the packing density of the blend: less dense for PS/PPO and PS/PVME; more dense for PMMA/PEO. Comparison of average free volume hole sizes and fractional free volumes measured via orthopositronium annihilation lifetime measurements for all three blends versus the pure constituents are qualitatively consistent with this interpretation. Second, because of the presence of concentration fluctuations in the blend, it is expected that the initial stress decay is dominated by regions enriched in the more mobile component. From observations of the change in width of the stress relaxation time distribution, this effect appears to be particularly significant in the PS/PVME blend. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 483–496, 1997     

Dielectric Investigation of Molecular Dynamics of Blends: IV. Effect of Blending on the Normal Mode Process of Polyisoprene/Polystyrene Blends

Polyisoprene/polystyrene (PI/PS) blends have been prepared and investigated for compatibility using dielectric and calorimetric measurements. Various blends were prepared from polystyrene (number average molecular weight, — _n=160 000 g mol^-1) and polyisoprene with — _n values of 13 800, 40 500 and 130000gmol^-1. Dielectric measurements have been carried out over a wide frequency range (10^-2–10⁶Hz) and in the temperature range of the glass and normal mode processes (-70 to +70°C). The glass transition, as well as the corresponding relaxation process, of polyisoprenes were shifted to higher temperatures in the different blends, indicating compatibility. The blends showed a lower critical solution temperature (LCST) at temperatures above 105°C. It was surprising to find that blending of polyisoprene with polystyrene led to a great shift to higher values in the relaxation frequency of the normal mode process for the isoprene segments. The measurements showed that the relaxation time of the normal mode process in the blends was longer than that of the glass process by a constant factor (3·2 decades), regardless of the molecular weight of the polyisoprenes used in the blends. This finding implied that the domain length responsible for the compatibility of the two polymers was consistent regardless of the molecular weight used (where — _n> — _c, the critical molecular weight). In view of the results obtained, and by using a molecular model, it was possible to determine the size of the structural domains responsible for the compatibility. The value obtained (16·7nm) is very similar to that suggested to be responsible for the glass transition in pure polymers. © 1997 SCI.     

Thermodynamic aspects of the glass-transition in the compatible blend poly(styrene)-poly(vinylmethylether)

Summary It is shown that composition dependence of glass-transition in the compatible poly(styrene)-poly(vinylmethylether) blend exhibits deviations from additivity rules derived in the supposition of continuity of the thermodynamic excess functions of mixing. Only the acceptance of an additional adjusting parameter which accounts for interaction, enables the interpretation of experimental T_g-data. This adjusting parameter is quite different for the blends of PVME with oligomeric and high moleculare PS, respectively. Dedicated to Prof. C. I. Simionescu's 65th Birthday     

Microheterogeneity in PPO/PS blends

Proton spin magnetization relaxation in the rotating frame is a simple exponential for poly(2,6-dimethylphenyleneether) (PPO) (23K)/polystyrene (PS) (9K) blends of various compositions; these blends are truly homogeneous at the spin-diffusion distance scale of a few nanometers. Blends of PPO with high molecular weight PS exhibit nonexponential decays for the PS component but exponential decays for the PPO component, indicating compositional fluctuation for PS. In some blends, the relaxations are nonexponential for both components. Three factors have been identified to promote microheterogeneity of nanometer dimensions: high polymer molecular weight, increase of temperature, and preparation of blend using solvent that induces crystallization of PPO such as toluene.     

Orientation and relaxation in uniaxially-stretched poly(2,6-dimethyl 1,4-phenylene oxide) — atactic polystyrene blends

Infra-red measurements of the dichroic ratio of atactic polystyrene and poly(2,6-dimethyl 1,4-phenylene oxide) absorption bands provide a valuable method for the determination of orientation as well as relaxation of chains of both polymers during stretching of their compatible blends. Influence of strain rate, temperature of stretching, and molecular weight of the polymers on orientation of both polymer chains in blends containing up to 35% PPO has been studied. Orientation relaxation for both polymers has been analysed using Lodge's constitutive equation. Master curves have been obtained for PPO and PS in the blends at a reference temperature T₀ = T_g + 10°C. Results are interpreted in terms of an hindrance of relaxation of PS chains induced by interaction with a highly-oriented PPO network which slowly relaxes.     

Interaction in polymer blends via dilute solution light-scattering under optical θ-conditions

Summary It is demonstrated that dilute solution light —scattering experiments under ‘optical θconditions’ offer rapid and reliable judgement of the interaction parameters in polymer blends. This has been verified with miscible blends of polystyrene with poly(vinylmethylether) and with the immiscible pair polystyrene —poly(vinylisobutylether). The capabilities of the optical θ-approach in order to derive the influence of polymerpolymer interaction on chain dimensions are discussed shortly. Herrn Dr. B. Sedlacec zu seinem 60. Geburtstag herzlichst gewidmet     

Static and kinetic studies of polystyrene/poly(vinylmethylether) blends

A systematic study of static and kinetic phase behavior of deuterated polystyrene/poly(vinylmethylether) blends is presented in this paper. The static properties are studied by the small angle neutron scattering techniques and the kinetics of phase decomposition are studied by the temperature jump light scattering; technique. This procedure provides detailed information about phase behavior with regard to both thermodynamics and kinetics.     

Phase separation in polymer blends comprising copolymers: 5.

Dynamics of the miscible blend of poly(vinyl methyl ether) and poly(4-vinylphenol) [PVME/PVPh] have been studied using broadband dielectric relaxation spectroscopy (DRS). The results are compared with those reported for PVME/polystyrene [PS] and PVME/poly(2-chlorostyrene) [P2CS] blends to examine the effect of intermolecular hydrogen bonding. These blends have similar chemical structures, with the exception that strong intermolecular hydrogen bonds are formed between PVME and PVPh. Whereas PVME and P2CS (or PS) relax individually in their blends due to intrinsic mobility differences and the absence of strong intermolecular interactions, the segmental relaxations of PVPh and PVME are coupled in the blends controlled by intermolecular hydrogen bonding. Dynamic heterogeneity was observed in PVPh/PVME blends with PVPh concentration higher than 50%. This is due to the decoupling arising from the strong intramolecular hydrogen bonding between PVPh segments. Finally, in the blend, the secondary relaxation processes of both components occur at approximately the same temperature-frequency location as those in corresponding neat polymers, but with much lower intensity, suggesting suppression by the intermolecular hydrogen bonding. Our results suggest that the composition-dependent dynamics in PVPh/PVME are even more complicated than that observed in blends without strong intermolecular interactions.     

Composition-dependent dynamics in miscible polymer blends: influence of intermolecular hydrogen bonding

Dynamics of the miscible blend of poly(vinyl methyl ether) and poly(4-vinylphenol) [PVME/PVPh] have been studied using broadband dielectric relaxation spectroscopy (DRS). The results are compared with those reported for PVME/polystyrene [PS] and PVME/poly(2-chlorostyrene) [P2CS] blends to examine the effect of intermolecular hydrogen bonding. These blends have similar chemical structures, with the exception that strong intermolecular hydrogen bonds are formed between PVME and PVPh. Whereas PVME and P2CS (or PS) relax individually in their blends due to intrinsic mobility differences and the absence of strong intermolecular interactions, the segmental relaxations of PVPh and PVME are coupled in the blends controlled by intermolecular hydrogen bonding. Dynamic heterogeneity was observed in PVPh/PVME blends with PVPh concentration higher than 50%. This is due to the decoupling arising from the strong intramolecular hydrogen bonding between PVPh segments. Finally, in the blend, the secondary relaxation processes of both components occur at approximately the same temperature-frequency location as those in corresponding neat polymers, but with much lower intensity, suggesting suppression by the intermolecular hydrogen bonding. Our results suggest that the composition-dependent dynamics in PVPh/PVME are even more complicated than that observed in blends without strong intermolecular interactions.     

Thermal and swelling properties of polystyrene-polyolefin blends

Model blends of glassy amorphous polystyrene and each of four different crystallizable and rubbery polyolefins of varying side-chain molecular weight (polyethylene, polypropylene, poly(1-butene), poly (4-methyl-1-pentene)) have been prepared by melt extrusion of the polymeric components. Density measurements, differential scanning calorimetry (DSC), swelling measurements, and X-ray diffraction have been performed on the extruded fibers. In all cases, over the entire range of blend composition, the polymeric blends are immiscible and incompatible. The DSC measurements indicated that the polystyrene T_g was not decreased after blending and that the small reductions in the crystallinity and melting point of the respective polyolefins was best explained by thermal and kinetic interference with homo-crystallization of the respective polyolefins in the blends. The volumetric swelling and gravimetric sorption of n-hexane in the various blends increased monotonically with polystyrene content. The companion experiments, relating axial swelling with polystyrene content, indicated that this particular mode of distension actually decreased with increasing polystyrene content. The composite results, including DSC, X-ray, density, volumetric swelling and axial swelling suggest that the polystyrene phase is essentially microfibrillar and oriented in the direction of extrusion.     

Effect of deformation on the surface composition of multicomponent polymers: Blends of poly(dimethyl siloxane) in polychloroprene

X-ray photoelectron spectroscopy and scanning electron microscopy are used to follow the effect of uniaxial stretching on the surface composition and morphology of poly(dimethyl siloxane)/poly(chloroprene) blends. Before stretching, the blends exhibit a high surface segregation of siloxane due to an extremely low surface energy of the latter. The stretching gives rise to a substantial drop in the siloxane surface enrichment, whereas the subsequent unloading has the reverse effect. The surface behavior of the blends upon deformation strongly depends on the molecular weight of the siloxane component. Oligomeric siloxane (MW = 2500) shows a much stronger surface depletion with stretching, compared to that observed with a siloxane polymer (MW = 625,000). Furthermore, the surface behavior of the blends of the polymeric siloxane is completely reversible in sample length, whereas the blends of the oligomeric siloxane have different surface compositions on stretching and contraction. © 1996 John Wiley & Sons, Inc.     

Control of structure and mechanical properties for binary blends of poly(3‐hydroxybutyrate) and cellulose derivative

Structure and mechanical properties for binary blends composed of a poly(3‐hydroxybutyrate) (PHB) and a cellulose derivative, such as cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB), have been studied by means of dynamic mechanical analysis, isothermal crystallization measurements, and tensile testing. It is found that β relaxation temperature due to glass transition of PHB or PHB‐rich phase in the blends, in which the cellulose derivative has lower molecular weight, is almost the same as that of the pure PHB. On the other hand, the peak location is shifted to even lower temperature than that of the pure PHB by blending the cellulose derivative with higher molecular weight, although the cellulose derivative is a glassy polymer with high glass transition temperature. Further, the blend with lower β relaxation temperature exhibits ductile behavior with low modulus in uniaxial deformation. The difference in the structure and mechanical properties for the blends are found to be determined by the crystallization rate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3447–3452, 2007     

Phase separation in polymer blends comprising copolymers: 5. Polyisoprene/poly(isoprene-g-styrene) copolymer system

As part of a programme of research into miscibility in polymer blends comprising copolymers, this paper presents the morphology of blends of polyisoprene and poly(isoprene-g-styrene) with complicated but well defined structure. The graft copolymers were prepared by polymerization of styrene initiated by metallated polyisoprene backbone and were fully characterized. All the studied blends of copolymers and polyisoprene of different molecular weights exhibit macrophase separation even when the molecular weight of the homo PI is apparently less than that of the PI segments between neighbourning junction points in the copolymers. The results provide support for the argument that the molecular architecture of a copolymer is an important factor governing its miscibility with corresponding homopolymers. Besides, it is observed that the copolymer with higher proportion of polystyrene shows apparent solubilization in polystyrene matrix of high molecular weight and solubilization varies predictably with the addition of low molecular weight polyisoprene.     

Surface segregation of components in poly(vinyl chloride)–polydimethylsiloxane and polystyrene–poly(propylene oxide) solvent-cast blends

X-ray photoelectron spectroscopy and scanning electron microscopy are used to study the surface composition and morphology of poly(vinyl chloride)–polydimethylsiloxane (PVC–PDMS) and polystyrene–poly(propylene oxide) (PS–PPO) solvent-cast blends as a function of the blend composition and constituent molecular weights. The PVC–PDMS blends show a pronounced surface enrichment of PDMS, which is higher the lower the molecular weight of PDMS. The surface behavior ofthe PPO–PS blends is strongly dependent on the solvent used. Despite the much lower surface tension of PPO compared to that of PS, no surface segregation of PPO isobserved in the PPO–PS blends cast from tetrahydrofuran, while the blends cast from chloroform exhibit a high surface enrichment of PPO. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 517–522, 1998     

Orientation and relaxation in uniaxially stretched poly(vinyl methyl ether)-atactic polystyrene blends

Infrared measurements of the dichroic ratio of polystyrene and poly(vinyl methyl ether) absorption bands allow us to determine chain orientation for each component in their compatible blends. Influence of strain rate and temperature of stretching on orientation of both polymer chains in blends containing up to 25% PVME has been studied. Mechanical relaxation master curves at a reference temperature T=T_g+40°C have also been determined. Results are compared to previous results obtained in PS-PPO compatible blends. Although PPO and PVME chains behave differently PS chains behaviour is similar in the two types of blends and interpreted in terms of a hindrance of relaxation of PS chains induced by a modification of friction coefficients due to the molecular interactions which are at the origin of compatibility.     

Adhesive properties of DGEBA–acid homopolymer and DGEBA–acid copolymer systems

Adhesive properties of high molecular weight acid copolymers used as hardeners for a commercial epoxy resin are investigated. For comparative purposes, physical blends of poly(acrylic acid)–polystyrene are used as hardeners. Joints prepared from physical blends exhibit lower lap shear strength than do those prepared form synthesis products. The use of copolymers is more adequate. Thermodynamic work of adhesion using wettability criteria is explored to explain the differences. The apparent energies of rupture determined by lap shear tests are 10³ higher than those of the thermodynamic work of adhesion. © 1995 John Wiley & Sons, Inc.     

Charge storage of ternary polymer blends based on poly(phenylene ether)

BACKGROUND: Charge storage capability is a fundamental property of polymers used in electromechanical transducer applications. In this work, the charge retention of ternary blends of poly(phenylene ether) and polystyrene modified with poly(styrene‐co‐acrylonitrile), polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene or polystyrene‐block‐polyisobutylene‐block‐polystyrene (SIBS) triblock copolymers was correlated with the blend composition, final morphology and the chemical structure of the components. RESULTS: It was determined that the charge storage capability is favoured by a finely dispersed and non‐interconnected phase and can be reduced by high polarity or low molecular weight of the blend components. Additionally, the molecular weight and the amount of styrene of the copolymers also determined the phase morphology, which in turn affected the charge retention. The use of SIBS for the ternary blends, especially in small quantities, significantly improved the charge storage. As such, 100 µm films with a surface potential of about 400 V were able to retain up to 240 V (60%) after 24 h at 130 °C. CONCLUSION: The electret behaviour of the polymer blends was influenced by a complex relationship between chemical structure, molecular weight and phase morphology. Copyright © 2009 Society of Chemical Industry     

Mechanical and morphological behavior in polystyrene based compatible polymer blends

Mechanical and morphological behavior of polystyrene (PS) based compatible polymer blend systems were studied using a tensile tester and scanning electron and optical microscopes. Four different binary compatible blend systems were employed and characterized: PS and poly (2,6-dimethyl 1,4-phenylene oxide) (PPO), PS and poly(vinylmethylether)(PVME), PS and poly(α-methyl styrene)(PαMS), and PPO and PαMS. The compositional dependence of the mechanical properties showed a synergistic effect with respect to modulus, but a negative deviation from the rule of mixtures relationship for strain at break. From the scanning electron microscope (SEM) observations, a deformation mode transition from crazing to crazing and shear banding occurs at ˜25 wt% PPO in the PS/PPO blends, as indicated by the patch and river patterns above this composition. In the PS/PVME blends, a similar transition was observed at >10 wt% PVME. The PS/PαMS blends showed brittle fracture regardless of composition. The PPO/PαMS blends showed a brittle fracture for a PαMS content >25 wt%. Optical microscope (OM) observations showed that blending of PS/PPO and PS/PVME resulted in a decrease of craze density and length as the PPO and PVME content was increased. PS/PαMS and PPO/PαMS blends showed few crazes, all of which were localized near the fracture surface. The mechanical and morphological behavior can be explained using models of intermolecular interactions and entanglement density in compatible blends, respectively. Overall the mechanical property and the consequent morphological behavior were similar to the effect of antiplasticization.     

通过状态方程预测无定形和可结晶共混聚合物的压力-体积-温度和超摩尔体积（英文）

In this work the statistical mechanical equation of state was developed for volumetric properties of crystal ine and amorphous polymer blends. The Ihm–Song–Mason equations of state (ISMEOS) based on temperature and density at melting point (Tm andρm) as scaling constants were developed for crystalline polymers such as poly(propylene glycol)+poly(ethylene glycol)-200 (PPG+PEG-200), poly(ethylene glycol) methyl ether-300 (PEGME-350)+PEG-200 and PEGME-350+PEG-600. Furthermore, for amorphous polymer blends con-taining poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)+polystyrene (PS) and PS+poly(vinylmethylether) (PVME), the density and surface tension at glass transition (ρg andγg) were used for estimation of second Virial coefficient. The calculation of second Virial coefficients (B2), effective van der Waals co-volume (b) and correction factor (α) was required for judgment about applicability of this model. The obtained results by ISMEOS for crys-talline and amorphous polymer blends were in good agreement with the experimental data with absolute aver-age deviations of 0.84%and 1.04%, respectively.