1994 рік

Cloud-point measurements were made on quasi-binary mixtures of diglycidyl ether of bisphenol A (DGEBA) epoxy resin with poly(ether sulfone) (PES). The relative molecular masses of both resin and polymer were varied, and temperature-dependent Flory-Huggins interaction parameters were estimated on the assumption that both components are monodisperse. The data were used to calculate lower critical solution temperatures (LCST) and compositions, and to construct coexistence curves. The evolution of two-phase morphology during curing of epoxy-PES blends containing 4,4'-diaminodiphenylmethane (DDM) hardener is related to these results

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Liquid crystalline polymers are currently among the most widely studied classes of polymeric materials. The correlation of mesophase and liquid crystalline polymer molecular structures with observable physico-chemical properties is a major objective. In this work, inverse gas chromatography (i.g.c.) was used to determine the transition temperatures of a main chain, liquid crystalline, biphenyl-based organic polyester. The transition temperatures determined by using this method agree very well with those determined by other techniques. In addition, the i.g.c, experiment gives physico-chemical parameters for the interaction of probe molecules (saturated and aromatic hydrocarbons) with the liquid crystalline phases. Thus, enthalpies of mixing and solution of probe molecules in the polymer were estimated, and activity coefficients were calculated. From a single i.g.c, experiment, a wide range of information regarding the temperature-dependent properties of a liquid crystalline polymer was obtained

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The microstructure of polyurethanes and its evolution upon thermal treatment were investigated by means of small-angle X-ray scattering and low-frequency high-resolution mechanical spectroscopy. The segmented copolymer materials studied in this work were prepared in bulk and were completely amorphous as a consequence of the chemical composition of the soft and hard segments. This amorphous state results in model materials and, in principle, easier interpretation of the morphology from experimental results. It is shown in this work that thermal treatment induces a coarsening of hard-phase microdomains and an increase of the interfacial region, which remains of the order of a few ~mgstrSms. This morphology evolution leads, to some extent, to a weakening of the mechanical properties as observed above the glass transition temperature of the soft-phase matrix. The conclusion is that the synthesis conditions, as well as subsequent heat treatment, are to be carefully considered in order to obtain materials with well controlled physical properties.

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Two monoamidated amino compounds, bearing the cyclic disulfide moiety of lipoic acid, were prepared by imidazole group transfer with aliphatic diamines (1,3-diaminopropane and piperazine). The products, characterized by spectroscopic methods (1H nuclear magnetic resonance and Fourier-transform infra-red), were studied in solution. Basicity constants for the protonation of the basic nitrogens were evaluated in aqueous media, and redox properties in dimethylsulfoxide, by cyclic voltammetry. Insoluble polymers were obtained by polymer-analogue exchange reaction of the monoamidated compound with a benzotriazole residue present in preformed poly(N-acryloylbenzotriazole). A copolymer of the same monomer with N-vinylpyrrolidinone was soluble in solvents, giving a response in cyclic voltammetry. Its positive anode peak was slightly higher than that of the simple monoamidated compounds.

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In this paper, three novel silicon-containing polyimides (abbreviated as SiDA-TDA, SiDA-DDA and SiDA-BDA) were synthesized. The permeability to H2, 02 and N2 of these polymer membranes was determined at 30°C and at 1 atm. The introduction of bis(phenylcarboxylic dianhydride)dimethylsilane (SiDA) into the backbone of polyimides appears to result in a significant increase in gas permeability, without a correspondingly large decrease in permselectivity. The relationships between chemical structure and permeability of polyimides were also discussed. Wide-angle X-ray diffraction measurements of the average segmental spacing of the membrane materials characterized the packing of the different polymer types.

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Stray field nuclear magnetic resonance imaging has been used to study the diffusion of acetone vapour into poly(vinyl chloride) (PVC). For the first time in a n.m.r, imaging experiment the penetrant, the swollen polymer and the rigid polymer have been simultaneously visualized. Results are presented for a range of acetone vapour activities and sample preparation temperatures, and also for a sample prepared with deuterated acetone. The profiles show that the diffusion is of Case II type. A sloping profile is observed behind the penetrant front and is interpreted in terms of a softening of the swollen polymer, which occurs over a period of hours after penetration by the acetone. The softening rate has been measured as a function of temperature.

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Physical-chemical studies on a sample of NCH3-imidized poly(methyl methacrylate) (PMMA-I-CH3) were performed by several characterization techniques. Fractional precipitation by solvent/non-solvent at constant temperature was used, obtaining 12 fractions characterized by different molecular weights. With these fractions of the PMMA-I-CH3, in the range 2 x 104< M w < 2 x 105, a Mark-Houwink equation was determined. This relationship, in tetrahydrofuran at 30°C, was found to be rr/] = 2.22 x 10 -4- Mw0 6 6 . This equation is the starting point for studying the polymer-structure relationships. The determination of various properties, such as viscosity, glass transition temperature, nitrogen content and molecular weights, allowed us to obtain structural information on the copolymer. The imidization degree, evaluated by ~H n.m.r. spectroscopy, was used to correlate glass transition temperature and polymer structure.

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A simultaneous interpenetrating polymer network (SIN) based on diglycidyl ether of bisphenol A (DGEBA) and poly(poly(ethylene glycol) maleate) (PPEGMA) in a 50/50 weight ratio was blended and was cured simultaneously by using benzoyl peroxide and m-xylenediamine as curing agents. Kinetic studies during SIN formation were carried out at 50, 60, 65 and 70°C. Concentration changes of both epoxide and double bonds were monitored with Fourier-transform infra-red spectroscopy. Rate expressions were established with model reactions. Experimental results revealed that lower rate constants and higher activation energies for SIN were found compared with those for the formation of the respective component networks. A network interlock effect was proposed to account for this phenomenon. During simultaneous cure of DGEBA and PPEGMA, network interlock must provide a sterically hindered environment, which subsequently increased activation energies and reduced cure rates for both DGEBA and PPEGMA.

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The Tt and T 2 proton n.m.r, relaxation times of water in aqueous sodium carboxymethylcellulose (NaCMC), with water contents below 2 gn2o/gcMc, were measured between 340 and 120 K. The n.m.r, study revealed that (1) a distribution of correlation times and a correction of the Bloembergen, Purcell and Pound (BPP) theory for rigid lattice protons at low temperatures is necessary to simulate T 2 as a function of temperature, (2) non-freezing water is associated with two energetically distinct sorption sites, and (3) non-freezing water exhibits a temperature dependent motional anisotropy. Above 260 K, water at high-energy sites is responsible for an increase of T2 with decreasing temperature. Below 260 K, T2 shows a two-step decline that is caused by translational motion of the water molecules at the higher temperature and by rotational motion in the lower temperature region. The above mentioned motions are attributed to the motion of water molecules associated with lower-energy binding sites. At temperatures below 200 K, a Pake-type lineshape can be observed due to the increasing number of immobile water proton pairs. From a simulated lineshape analysis, the ratios of rotating to stationary water molecules were calculated as a function of temperature and water content

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Interfacial polycondensation of bisphenol-A and phosgene is a well-known way to prepare bisphenol-A polycarbonate, the molecular weight of which can be controlled by the addition of suitable amounts of phenol. When the chain stopper is a bifunctional compound, the way is open to the synthesis of telechelic polycarbonates. 4-Hydroxybenzoic acid, 4-hydroxybenzenesulfonic acid, 4 N,N'-dimethylaminophenol and the iodoammonium derivative have been used as bifunctional chain stoppers in the synthesis of acid and amino telechelic polycarbonates. The n.m.r, analysis of the final products has provided evidence for the successful synthesis of ~t,to-tertiary amino and ~,co-quaternary ammonium polycarbonates. In contrast, fast transesterification reactions prevent ct,tn-carboxylic and sulfonic acid polycarbonate from being prepared in a controlled way

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