1994 рік

The zero-shear-rate viscosity and ion conductivity of a homologous series of polydimethylsiloxane (PDMS) oils and six homologous series of PDMS salts of various univalent cations (sodium, potassium, tetramethylammonium, tetraethylammonium, tetrapropylammonium and tetrabutylammonium) were measured over the temperature range -45°C

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In this work, the miscibility of poly(2-chlorostyrene) (P2CS) and poly(vinyl methyl ether) (PVME) mixtures was characterized and compared to polystyrene (PS)/PVME blends. It was found, by light scattering, that P2CS/PVME blends exhibit a lower critical solution temperature. Fourier transform infra-red spectra of these two blends indicate that the presence of the chlorine atom strengthens the attraction between the phenyl rings of P2CS and the electron lone pairs of the oxygen atoms on the PVME chains. This specific interaction is the main reason for the improvement of the miscibility of this particular blend in comparison to PS/PVME. These experimental results are in accord with the magnitudes of the binary interaction parameters, X, of P2CS/PVME and PS/PVME blends estimated from the cloud point data based on the mean-field theory. The experimental results obtained in this work provide a molecular basis for the interpretation of polymer-polymer miscibility.

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Particle masses of the order of 108-101° gmo1-1 and the radii of gyration and hydrodynamic radii of spherical poly(methyl rnethacrylate) particles were characterized by combined static and dynamic light scattering. The dispersions were prepared by dispersion polymerization and stabilized by polystyrene-blockpoly( ethylene-co-propylene). The radii of gyration were calculated from the measured particle scattering intensity by fitting procedures using the Rayleigh formula for spheres. This practice allows the use of all points actually measured instead of the uncertain values at low angles only. The strongly disturbing influence of small contents of large particles (aggregated particles, dust) was eliminated. The autocorrelation functions were measured by dynamic light scattering and analysed by the Contin procedure. The coronas and densities of the particles could be characterized on the basis of the geometric radii of the pure main components.

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A homologous series of polydimethylsiloxane (PDMS) oils was doped with varying amounts of PDMS salts of three different univalent cations (sodium, tetramethylammonium and tetrapropylammonium). The zero-shear-rate viscosity and ion conductivity of each sample were measured over the temperature range - 50°C < T< 60°C. Free volume and Arrhenius type viscosity and ion conductivity models were successfully applied to these data. The effects of mobile ion concentration on the values of the best-fit model parameters were explored.

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Investigation of the nature of the freezing bound water in xanthan hydrogels by differential scanning calorimetry (d.s.c.) reveals a dependence of the area, temperature and number of the freezing exotherms on the period of time that the gel was maintained at a temperature greater than the gel-sol transition temperature (T*). Small-angle X-ray scattering (SAXS) and synchrotron orbital radiation (SOR) experiments show a correlation between the holding time of the gel at temperatures in excess of T* and the size of the junction zones which maintain the integrity of the gel. High-temperature annealing also increases the elastic moduli of the gels. These results are discussed in terms of a general model for the dynamic structure of polysaccharide junction zones previously proposed by the authors.

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The electron spin resonance (e.s.r.) spectra of nitroxide end-labelled poly(methyl methacrylate) (PMMA) were recorded over a temperature range for the pure, bulk polymer and for l:l (w/w) immiscible blends with poly(2-ethylhexyl methacrylate) (PEHMA) and polystyrene (PS). The changes in the e.s.r, spectra brought about by blending and varying the temperature show that chain ends tend to congregate in the interphase region. In the blends of PMMA and PEHMA the chain ends of the PMMA in the interphase are mobilized through plasticization by the rubbery PEHMA. This phenomenon was observed previously in blends of end-labelled PS with unlabelled polyisoprene. Our present results, particularly from the PMMA-PS blends, reveal that an additional enhancement of mobility of chain ends results from the accumulation of free volume in the interphase

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In poly(propylene glycol) (PPG) the polymer chains are terminated by hydroxy groups. These polar ends are capable of coordinating to both cations and anions when a salt is dissolved in the polymer. This coordination has been monitored using shifts in the OH stretching vibration band at about 3400cm-1, as measured by Fourier transform infra-red spectroscopy. In the LiCF3SO3-PPG(3000 ) system, the Li ? ions preferred to coordinate to OH groups rather than to ether oxygens; at the composition LiCF3SOaPPGlo, all OH groups were coordinated by both lithium and triflate ions, suggesting that the properties of these electrolytes depend to a large extent on metal ion to OH end-group interactions. Solvent-shared ion pairs, where the ions are separated by an OH group rather than free triflate ions, are present in these samples. The triflate ions in the solvent-shared ion pairs are suggested to have a 1,'(SO3) s absorption band at 1032 cm-1, i.e. at the same position as has been found for non-coordinated triflate ions.

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The dipolar relaxation behaviour of poly(vinyl acetate) has been studied extensively in the low temperature region from -160 to -20°C. It is shown that the observed relaxation peak does not correspond to a single relaxation process but to a continuous distribution of relaxation times. The components of this distribution show Arrhenius behaviour and the corresponding activation energies are low ( ~ 8 kcal mol- 1), which suggests that the dipolar motions involved are local motions, probably internal rotations about single bonds in the acetate groups. A continuous increase of the Gibbs activation energy for higher temperature components is observed, which is a consequence of a lowering of the activation entropy (the higher temperature relaxation modes have more negative activation entropies).

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The stereochemical structures of samples of poly(ethyl acrylate) (PEA), poly(butyl acrylate) (PBuA) and poly(2-ethylhexyl acrylate) (PEHA), prepared by group transfer and anionic polymerization, were studied by 13C and 1H n.m.r, spectroscopy. The main-chain CH 2 spectral range was analysed by the application of the inverse 13C-1H HETCOR two-dimensional n.m.r, technique. A very similar HETCOR pattern was found for all polymers studied. In all cases, main-chain CH2 lines in the 1H and 13C n.m.r, spectra could be assigned to configurational tetrads; for PEA and PBuA a partial assignment of carbon resonances to configurational hexads was possible. While PEHA prepared both by group transfer and anionic polymerization and PEA prepared by group transfer polymerization can be well approximated by Bernoullian statistics, for PEA and PBuA prepared by anionic polymerixation a first-order Markov model is required to fit the observed intensities at the hexad level.

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End-group coordination has been studied using poly(propylene glycol) with a molecular weight of 3000 (PPG(3000)) terminated with hydroxy groups. On dissolution of different lithium salts LiX in PPG(3000) for X = PF6, BF~, CIO~, CF3SO3, I-, Br- and CI-, shifts of the OH stretching band were observed using Fourier transform infra-red spectroscopy. The size of the shift is dependent on the strength of the hydrogen bond formed between the OH group and the anion of the salt. A cation dependence of the OH stretching band was also found using KPF 6. There are two dominating coordination structures involving the OH groups present in the samples. One is a solvent-separated ion pair where the anion and cation are separated by an OH end-group, and the other is an OH group coordinated both to the cation of the salt and to an ether oxygen from the polymer.

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