1992 рік

Small angle neutron scattering measurements were performed on a ternary blend of deuterated polystyrene (PSD), poly(vinylmethyl ether) (PVME) and protonated polystyrene (PSH) for sample temperatures ranging from ambient to 160°C (close to the spinodal decomposition temperature). The extension of de Gennes' random phase approximation formula for the structure factor to three components was used to analyse the data. Two of the Flory-Huggins interaction parameters were obtained from the published literature (XPsD/Psn and ZPSD/PVME) and the third, ZPSn/VVME, was extracted from fits to the SANS data. Two different samples corresponding to the same PVME composition but different PSH/PSD fractions gave similar dependences: Zpsn/evM~/Vo = 10.3 x 10 -4- 0.422/T and Zpsn/eVuE/Vo = 10.6 X 10 -4 -- 0.436/T, where T is the absolute temperature. Plots of g versus 1/T show a uniform shift of around 20°C (downward in temperature) in going from the PSD/PVME to the PSH/PVME blends.

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The generation of Brownian dynamics trajectories for a flexible polymer constituted of statistical Gaussian units with intramolecular long-range (excluded volume) interactions is accomplished. The intramolecular interactions are described by relatively soft repulsive forces derived from an exponentially decaying potential with a cut-off distance. The validity of this method is satisfactorily tested through the comparison of a wide set of numerical results for equilibrium properties (different averaged dimensions and internal distances, and the end-to-end distance distribution factor) with Monte Carlo results from a model that includes the customary hard-spheres representation of excluded volume forces. Furthermore, the numerical values obtained in this study for the different properties are shown to agree with the scaling theories or Renormalization Group predictions. A transport property, the translational diffusion coefficient, is also obtained and included in the numerical analysis.

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Attenuated total reflectance Fourier transform infra-red (ATR FTi.r. ) spectroscopy was utilized to quantify the concentration of Si-H groups formed on poly (dimethylsiloxane) (PDMS) elastomer surfaces as a result of Ar or N 2 plasma modifications. Kramers-Kronig transformation of the ATR spectra of standard solutions containing Si-H species allows construction of calibration plots which are independent of the angle of incidence, crystal coverage and sample refractive index. The Si-H concentrations of the plasma-treated PDMS are calculated from the calibration plots, and indicate that gas/plasma treatments of PDMS substrates result in Si-H functionality gradients with higher concentrations near the elastomer surface.

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The polymerization of diepoxide-diamine is simulated using a two-stage procedure. In the first stage a convenient epoxy or amine excess is used to prepare a liquid prepolymer at complete conversion, which is then cured in a second step by balancing stoichiometry. The possibility of a secondary addition of the excess monomer is also considered. The extent of reaction leading to gelation in the second stage is obtained analytically for ideal systems and numerically when substitution effects in the amine hydrogens are taken into account. By selection of an appropriate initial stoichiometry, the gel conversion in the second stage may be considerably reduced when compared to the typical one-stage stoichiometric system (pBe~=0.6). This may have practical applications for reducing residence times in heated moulds or to freeze a phase separation process produced in the first stage of the polymerization.

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The five independent elastic moduli of extruded rods of two thermotropic liquid crystalline polymers, Vectra B900 and Vectra A950, and the nine independent moduli of an injection-moulded bar of Vectra A950 have been measured by ultrasonic methods at 10 MHz. For Vectra B900, the sharp rise in the axial extensional modulus C33 and the moderate drop in the transverse modulus C 11 with increasing draw ratio result from the alignment of molecular chains along the extrusion direction. The chain orientation also leads to an anisotropy in the shear modulus, with the axial shear modulus (C44) exceeding the transverse shear modulus (C66) by > 50%. The mechanical anisotropy in the surface layer of the injection-moulded bar implies that the chains lie mostly in the plane parallel to the wide surface of the bar, and preferentially along the injection direction. The weak anisotropy in the core indicates almost random molecular orientation. Based on the aggregate model, the upper (Voigt) and lower (Reuss) bounds of the elastic modulus of isotropic Vectra B900 have been calculated by using the modulus data of the oriented samples. The observed modulus of isotropic Vectra B900 lies within these bounds and is quite close to the lower bound.

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Gas formation mechanisms were studied in detail to find means for the selective recovery of specific components through catalytic gasification of polyethylene. Isobutene and butanes were obtained, respectively, by fl-scission from chain-end tertiary carbonium ions and by the hydrogenation of butene. The selective recovery of isobutane was possible by controlling reaction conditions such as temperature, reactor shape and, particularly, the exit temperature for gaseous products

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Rubber swelling theory is revisited in an attempt to derive consistent thermodynamic expressions for the elastic free energy valid for the swelling of a crosslinked polymer by liquids, gases or supercritical fluids. In this approach, evaluation of solvent properties in a hypothetical reference state is not needed. An equation of state for the crosslinked polymer is presented which may be used for the evaluation of its internal pressure. Model calculations are compared with experimental data on the swelling of crosslinked poly(dimethylsiloxane) by benzene and supercritical carbon dioxide.

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The optical properties of polyEoxyisophthaloyloxy-(2-methoxy-p-phenylene)methylidene-(2-oxo-l,3- cyclohexanediylidene)methylidyne-(3-methoxy-p-phenylene)] (I) and poly[oxysebacoyloxy-(2-methoxyp- phenylene ) methylidene- ( 2-oxo- 1,3-cyclohexanediylidene ) methylidene- ( 3-methoxy-p-phenylene )-] (II) polymer films were studied. The transmission and absorption measurements were carried out in the energy range 1.9-3.2 eV at 300 K. The data on absorption coefficient versus photon energy were analysed and interpreted in terms of the Tauc model, (~h~o)~/2 = BX/2 (hto - Egpt). Analysis of experimental results shows that the absorption characteristics give a good fit to the Tauc model, and indicates that both polymers I and II have an indirect band gap. The values of the optical gap E~ pt and the slope of the Tauc plots B 1/2 were determined. The study shows that the indirect allowed optical transitions are the predominant transitions in the optical absorption process. From the data a correlation between optical band gap and polymer structure was observed and discussed.

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The preparation and characterization of several finely tailored anthracene-backboned polyesters are discussed. The anthracene fluorescence lifetimes (z), fluorescence quenching kinetics (kq) and charge transfer equilibria (Kct) of the polymer-bound anthracene moieties (determined in chloroform) are also reported. Charge transfer complexation between the anthracene moiety and tetrachloro-l,4-benzoquinone (chloranil) is also investigated. In order to determine the extent of donor-accepter equilibria, Ket are determined from Benesi-Hildebrand plots. These results are correlated to the overall effects of the aliphatic bridging group, which appear to influence the micropolarity and vibrational and rotational properties of the anthracene moiety.

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This paper presents the results of Raman scattering and i.r. transmission investigations of poly(propylene oxide) (M, = ~3000) complexed with various concentrations of lithium, sodium and potassium trifluoromethanesulphonate. Analysis of the i.r. and polarized Raman spectra of the SO3 stretching region, in conjunction with complementary data from other spectral regions, suggests the existence of three associated ionic species: two differently co-ordinated ion pairs and a triple ion. It is argued that the free ions which were previously postulated to exist in these polymer-salt complexes are really cation-anion pairs weakly interacting through the CF 3 end of the anion.

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