1994 рік

A spectroscopic study has been conducted for the analysis of electric field induced microstructural changes in a uniaxially drawn 75/25 vinylidene fluoride/trifluoroethylene copolymer. Based on the relative intensities of the infra-red active bands measured, changes in the average orientation of the CH2 dipoles after poling could be determined. Upon applying an electric field of 1.0 MV cm-1 to the sample, the mean-squared value of cos ct for the CH2 dipoles in the crystalline domain with respect to the film plane was found to change irreversibly from 0.46 to 0.34. Additionally, an increase in the degree of crystallinity of approximately 8% was observed after poling. Factor analysis was utilized in our spectroscopic analysis. Infra-red spectra for both the crystalline and amorphous regions have been constructed. These spectra are identical to those previously measured for isotropic samples. The conformational distribution for samples after poling contains a larger fraction of trans segments than unpoled samples

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Intermacromolecular complexation between poly(methyl methacrylate) and modified polystyrene (PS(OH)) with the introduction of strong proton-donating hydroxyl groups has been studied by means of viscometry and non-radiative energy transfer (NRET) spectrofluorimetry. By increasing the hydroxyl content in PS(OH), both the transitions from immiscibility to miscibility and then from miscibility to complexation in the toluene-cast blends can be realized. A stoichiometric complex (1 : 1 base ratio) forms when the hydroxyl content reaches a high (~24mo1%) value. The NRET studies present evidence that in the complex, the polymer chains prefer to form unlike segment pairs rather than like ones. An apparent solvent effect on complexation is also observed for both solution and solvent-cast films

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This paper examines in detail the phase behaviour of blends of ~-methylstyrene/acrylonitrile copolymers (:~-MSAN) with poly(methyl methacrylate) (PMMA), tetramethylbisphenol A polycarbonate (TMPC), poly(vinyl chloride) (PVC), poly(2,6-dimethy|-l,4-phenylene oxide) (PPO), poly(e-caprolactone) (PCL) and bisphenol A polycarbonate (PC), and compares these with the corresponding behaviour of blends based on styrene/acrylonitrile copolymers (SAN). Replacement of styrene with ~-methylstyrene widens the miscibility window with PMMA and PVC but narrows the miscibility window with TMPC. In addition, the phase separation temperatures for e-MSAN blends with PVC are higher while those with PMMA and TMPC are lower compared to similar SAN-based blends. PPO, PCL and PC were found to be not miscible with any of the ~-MSAN copolymers. Interaction parameters for these systems were evaluated where possible from their lower critical solution temperature type phase boundary using the lattice fluid theory of Sanchez and Lacombe. The interactions between various monomer unit pairs were deduced using a binary interaction model for copolymers. The interaction parameters obtained are translatable from one system to another. The results are discussed in terms of interactions between monomer unit pairs and equation-of-state or compressibility effects

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Molecular dynamics simulations were performed in an attempt to elucidate the molecular mechanism of a relaxation measured experimentally in poly(p-phenylene benzobisthiazole) (PBZT) fibres. Results for the coefficient of thermal expansion and tensile modulus parallel to the molecular axis agreed favourably with published experimental values. The X-ray peak intensity ratio of (200)/(010) versus temperature obtained from the simulations showed a variation qualitatively similar to that from experiments. The torsion angle between the benzobisthiazole and phenyl moieties increased with temperature. A distortion of the phenyl and benzobisthiazole moieties also occurred and the molecules were observed to undergo increased oscillatory ribbon-like motions perpendicular to the (010) plane as the temperature increased. Finally, translational oscillations of the molecules parallel to the c-axis occurred. These molecular motions are coupled to the tensile stress and could play a role in the relaxation.

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A high density polyethylene homopolymer was blended with a linear low density ethylene hexene copolymer over the composition range of 0-100%. The resistance to slow crack growth was measured by a notched tensile test under constant load at 42, 60 and 80°C. The morphology was varied by slow cooling, quenching and annealing at 129°C for 24 h. Whereas the resistance to slow crack growth increased by a factor of 10 6 over the composition range, the differences in morphology could only change the resistance to slow crack growth at the most by a factor of ~ 3. The effect of temperature was independent of the effect of composition on slow crack growth. The effects of molecular and morphological structure are discussed.

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The kinetics of the periodate oxidation of starch to dialdehyde starch have been studied thoroughly based on a reliable high-performance liquid chromatographic analysis. Investigation of the early stage of reaction has revealed that it proceeds initially following second-order kinetics. Later on, however, the resulting second-order model deviates from the experimental data. In order to get a model for the course of the total reaction, the kinetics have been approached from a different angle. Based on elementary kinetic principles, an appropriate model has been derived that can be used to simulate the oxidation process. An oxidation process performed semi-continuously has been modelled and compared with a batch process.

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The rheological behaviour of miscible blends of poly(methyl methacrylate) (PMMA) with poly(styrene-coacrylonitrile) (PSAN) and with poly(vinylidene fluoride) (PVDF), in the molten state, was investigated. For this study, both steady and oscillatory shear flow measurements were made for PMMA/PVDF and PMMA/PSAN blends, which were prepared by melt blending in a twin-screw compounding machine. The following observations were made from the experimental results obtained: (1) plots of the logarithm of the zero-shear viscosity (log r/ob) versus blend composition show positive deviations from linearity for the PMMA/PSAN blend system, but negative deviations from linearity for the corresponding PMMA/PVDF system, under isothermal conditions; (2) plots of log ~/ob versus blend composition for the PMMA/PVDF blend system show minimum values at certain blend compositions as the viscosity ratio of the constituent components becomes smaller than a certain critical value and; (3) logarithmic plots of the dynamic storage modulus (G') versus the dynamic loss modulus (G") for all of the blend compositions lie between those obtained for the constituent components in both of the PMMA/PSAN and PMMA/PVDF blend systems. The experimental results are interpreted by using a molecular viscoelasticity theory recently developed by Han and Kim.

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Proton lineshape and proton spin-lattice relaxation, Tip, measurements were made on blends of bisphenol chloral polycarbonate and perdeutero poly(methyl methacrylate) (PMMA). The solution-cast blends are optically clear and display a single thermal glass transition temperature, T v as reported. The proton lineshape and proton relaxation data are used to follow the dynamics of the polycarbonate in the blend. The glass transition process is monitored by lineshape collapse as a function of temperature and the sub-glass transition process associated with rr flips of the phenylene group is monitored by the proton T~p values as a function of temperature. The glass transition as viewed from the polycarbonate remains similar in character to the behaviour observed in pure polycarbonate. Below T v the lineshape consists of a broadened Pake doublet and above Tg a narrow Lorentzian grows in on top of the Pake pattern. The bimodal behaviour and the growth of the narrow line with temperature can be described by the Vogel-Tamman-Fulcher equation with T O values which decrease with PMMA concentration. The proton T~p data show antiplasticization in the form of suppression of the ~ flip process as PMMA is added. In addition, a new minimum associated with the motion of the polycarbonate is observed at the temperature and time scale of the ester group rotation of the PMMA. This apparent coupling of the sub-Tg relaxation processes is related to the behaviour of polycarbonate upon addition of low-molecular-weight ester diluents. The level of antiplasticization and the amount of coupling is underestimated by a lattice model and an assumption of random mixing. On the very local scale of the n flip motion and at the higher concentrations of PMMA, there are apparently fewer PMMA-polycarbonate contacts than a random mixing assumption indicates.

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The effectiveness of the Sodium ionomer of poly(ethylene-co-methacrylic acid) as a compatibilizer for poly(ethylene terephthalate)/linear low density polyethylene (PET/LLDPE) was investigated at various PET/LLDPE ratios and ionomer contents. The techniques used were optical and electron microscopy, dynamic mechanical spectroscopy, differential scanning calorimetry and tensile tests. The tensile properties were characteristic of mechanical compatibilization since all other techniques indicated a phase-separated system. The PET/LLDPE ratio influenced the degree of compatibilization obtained. Using moderate levels of the compatibilizer (ca. 10 wt%), best properties were obtained at increased PET levels. On the basis of previous findings on the compatibility of PET/ionomer blends it is proposed that compatibilization should be attributed to strong interfacial bonding at the PET/ionomer interphase. An attempt to predict ternary properties from binary blend data using the appropriate theory of mixtures was moderately successful.

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A study of the effective charge density of a charged membrane composed of poly(vinyl alcohol) and poly(sulfonate) was carried out. The ratio of the effective charge density obtained from the membrane potential to the net charge density from pH titration was shown to be a function of degree of hydration (H). In order to explain the decrement of the ratio cited above as H increased, a model that includes two kinds of ionic fluxes within the membrane was introduced. This model was found to be able to give a qualitative explanation for the behaviour of the effective charge density of a charged membrane.

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