H. A. Schneider

DSC and TMS study of polystyrene/(poly(α-methylstyrene) blends

SummaryIt is shown that Tg data of PS/PaMS blends are influenced by the pressure applied during the preparation of compression-moulded samples. It is supposed the pressure favours the chain alignment of stiffer polymers in the neighborhood of binary contacts, contributing thus to the reduction of the freee volume. As a consequence compression-moulded samples will show increased Tg temperatures compared with those of the solution blended samples.

Pressure influence on the glass transition of polymers and polymer blends

Summaryp-V-T measurements have been carried out on a broad series of polymers and polymer blends. The effect of pressure on the glass transition temperature, Tg, and on related properties-increments of the coefficients of expansion, Δα, and compressibility, ΔK, at Tg-has been evaluated critically. The results are discussed in terms of the free volume, the order parameter, and the statistical mechanical theory. It is concluded that neither the simple ‘free volume’ theory, nor the order parameter theory in the one order assumption predict correctly the observed behaviour. A possible explanation of the phenomena observed is offered assuming an expansion of the free volume, which is independent of the nature of the polymer. For the blends binary contacts between the components are discussed, with respect to interaction energy and to conformational rearrangements.

Donor-acceptor complexation in macromolecular systems

SummaryBlends of donor-macromolecules — poly(N-(2-hydroxyethyl)-carb-azolyl)methacrylate — with acceptor-macromolecules — poly(methacryloyl-β-hydroxyethyl-3,5-dinitrobenzoate) — exhibit unique dynamic mechanical properties over a broad range of frequency and temperature when compared with those of the components. The complexation between the unlike polymers determines the topology of the thermoreversible network. Plateau modulus is extended into the low frequency and high temperature region dramatically. Corresponding copolymers show up minor improvement of the properties only depending on the donor-acceptor ratio within the macromolecular chain. Thus, the efficacy of intermolecular thermoreversible crosslinking clearly is evidenced.

Interactions in compatible polymer systems: 1. Viscoelasticity and glass transition of polystyrene-poly(vinylmethylether) blends

SummaryDynamic mechanical measurements on polystyrene — poly(vinylmethylether) blends are demonstrating that the relaxation processes in the blends are mainly connected with the motions of the poly(vinylmethylether) chain.Concerning the effect of mixing on topological properties of the blends, an increase of the polydispersity of the relaxation processes is detected in blends with high molecular weight polystyrene while low molecular weight polystyrene exerts an effect of dilution upon the relaxation of the high molecular poly(vinylmethylether) chains.From these measurements as well as from thermoanalytical data it results that the energetic interaction is more pronounced in the blends with oligomeric than with high molecular weight polystyrene. The glass transition temperature shows a larger deviation from additivity for blends with high molecular polystyrene than for those with oligomeric polystyrene.

Influence of flexible oligo(tetrafluoroethene) segments on the glass temperature of poly(aramide)s and poly(amide imide)s

SummaryThe insertion of oligo(tetraflouroethene) segments into the main chain of poly(aramide)s and poly(amide imimide)s is accompanied by a decrease of the glass temperature. The decrease is strictly related to the number of CF2-units and is the same for both poly(aramide)s and poly(amide imide)s. The absolute glass temperature depends, however, on the initial structures of the monomeric units. As a consequence ‘mastercurves’ can be constructed by shifting the individual Tg vs. number of CF2-units curves along the temperature axis. A detailed analysis of the data indicates that besides the Tg-mass/‘flexible’ bond of monomeric unit criterion additional volume and interaction dependant packing effects have to be considered for an accurate prediction of the glass temperatures of polymers.

Pressure-volume-temperature behaviour of molten polymers

SummaryThe solubility parameter theory of Hildebrand and Scott extended for polymer blends originally has accounted for dissimilarities only between contact energies of the blend components, neglecting free volume effects which are predicted by the corresponding states theories. Biroš et al., however, have shown that using expressions of the Prigogine-Flory corresponding state theories for energy and volume, effects of free volume will be implicity included in the solubility parameter approach too. The results are similar then to those derived by the corresponding state theories. In addition, it is shown that in this case the temperature and pressure dependencies of the solubility parameters are predicted qualitatively correct.We performed this procedure with the Sanchez- Lacombe EOS theory instead of the Prigogine-Flory approach, Formally, identical expressions result, and the calculated solubility parameters evaluated according to the two EOS theories are in good agreement. However, because Sanchez-Lacombes approach is not a corresponding state theory, it is able to predict additionally qualitatively correct the dependence of the solubility parameters on chain length.

Some remarks concerning the WLF-relation

SummaryThe limitations of the WLF-relation are discussed with respect to their inherent demands concerning universality. The problem of the reference temperature is discussed in some detail, and their constants are related to the temperature T∞ where the apparent activation energy of flow gets infinite, as well to the characteristic activation energy of viscous flow at infinitely high temperature, E∞.It is concluded that the use of experimentally derived temperature dependent apparent activation energy of flow, E(T), from the slopes of crossing isochrone and isotherm viscoelastic curves substitutes the WLF-relation favourably. Thus, the problematic choice of a reference temperature is avoided. The two kinetically specific constants, E∞ and T∞, may be admitted to characterize the energetic and entropic contribution, respectively, to the viscous flow. Experimental data are presented for some polymers.

Interrelations Between Shift Factors of Viscoelastic Functions and Apparent Activation Energy of Flow

SummaryThe applicability of an approach is tested experimentally, which interrelates the frequency as well as the temperature shift of isotherm and isochrone viscoelastic data with the apparent activation energy of the viscous flow. The procedure is based on the evaluation of the slopes of isotherms in the log viscoelastic function — log frequency plot and of isochrones in the log function — reciprocal temperature plot. Experimental data demonstrate that the approach applies over the entire temperature range from the high-temperature melt to the glass transition, where the WLF equation fails oftenly. The temperature range of variable activation energy turns out to be substantially smaller than supposed. Above Tg + 40 K constant activation energy suffices, suggesting that the range of validity of the EYRING model is quite larger than usually admitted.

Master surfaces of viscoelastic functions in the reciprocal temperature-frequency space

SummaryStarting from EYRINGs transition state theory it is demonstrated for systems obeying the superposition principle that the frequency shift factors of isotherm mastercurves of the viscoelastic functions as well as the temperature shift factors of the isochrone ones are unequivocally interrelated with the apparent activation energy of flow. The method for the evaluation of the activation energy from viscoelastic data is discussed, considering the moduli surfaces in the reciprocal temperature — frequency space. Experimental data prove the reliability of the approach. It is demonstrated that it is much more suitable to construct mastercurves as well as master surfaces in this way, because it is not necessary to apply measurements at low frequencies, which are unavoidable when the curves are constructed by empirical shift in the usual way.

Interrelations between relaxation distribution functions and apparent activation energy of flow

SummaryStarting from both the three-dimensional diagram of viscoelastic properties in the reciprocal temperature — log frequency — space and the time-temperature interrelation via apparent activation energy of flow, the possibility of theoretical interpretation of the isochronal behaviour is demonstrated, in analogy to the isothermal one. The determinative apparent activation energy of local flow is related with the relaxation spectra over the entire range of validity of the time-temperature superposition principle. Thus a theoretical background is offered for the method recommended before for the evaluation of the apparent activation energy of flow, which is applicable to calculate both isotherm and isochrone shift factors.