1999 рік

A sample of poly(methacrylic acid) [PMA] of molecular weight 50 000 was investigated as a function of its degree of neutralization and the concentration in pure water by X-ray scattering. Complementary potentiometric and viscosimetric studies were made in order to determine the range of ionization degree where the conformational transition occurs, and the limits between the dilute and semi-dilute regimes. Light scattering measurements show that filtered solutions of PMA are aggregate free. The scattering curves of the PMA in excess of chlorydric acid exhibit a q ¹3 behaviour in the high q range, which reveals the collapsed conformation of the chain at short distance. For the partially neutralized PMA, the peak of scattering curves, characteristic of the polyelectrolyte character, is shifted towards higher q values when the polymer concentration increases in agreement with the theoretical predictions. When the concentration is fixed, the q value at the peak maximum increases when the charge parameter increases, but a discontinuity appears in the range of the conformational transition.

Детальніше...  

The waterborne polyurethane (WPU) dispersions synthesized from poly(ethylene glycol) (PEG), dimethylol propionic acid (DMPA), and isophorone diisocyanate (IPDI) with various DMPA contents were prepared from our modified acetone process. Differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FT-i.r.), and wide-angle X-ray diffraction spectroscopy (WAXD) were utilized to characterize WPU films for the behavior of their crystallinity and H-bonding. Alternating current (AC) impedance experiments were performed to determine the ionic conductivities of WPU films and their corresponding gel electrolytes. One of the investigated WPU gel electrolytes exhibits an ionic conductivity as high as 10 ⫺5 S/cm at room temperature.

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The effects of the presence of trapped radicals after UV irradiation were studied on a dimethacrylate oligomer. The postpolymerization reaction was characterized by differential scanning calorimetry and dynamic mechanical analysis. The photopolymerization was realized with 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as radical photoinitiator by using isothermal photocalorimetry. The postpolymerization was clearly shown in the isothermal mode and under N2 atmosphere by following the variation of the glass transition temperature of the samples. The influence of crosslinking density, O2 and thermal postcure were investigated.

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Pseudo interpenetrating polymer networks were prepared by a sequential method using a high molecular weight natural rubber and poly(methyl methacrylate), PMMA. The thermal properties and morphology were investigated varying the average molar mass between crosslinks (M̄ c ) and the composition. The extent of crosslinking of natural rubber plays a major role in the transitions domains whatever the sample composition. As the crosslink density decreases, only one T g value is observed (M̄ c of 500 and 1000 g/mol). Comparison between the pseudo IPNs at different M̄ c values and compositions indicates that there are no significant differences in the thermal stabilities of the materials. Crosslinking and the component composition had a strong effect on the morphological patterns of the samples. For a higher crosslink density (M̄ c ¼ 142 g/mol), close and compact phase domains can be seen. The morphologies for lower crosslink densities (M̄ c of 500 and 1000 g/mol) showed fibrillar domains characteristic of the PMMA.

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The effect of oxygen or nitrogen containing functionality in model copolymers on the interfacial characteristics between the copolymers and metals was examined by adhesion strength and infrared spectroscopy. The adhesion strength with both copper and aluminum increased with increasing the vinyl pyridine (VP) content in poly (styrene-co-vinyl pyridine) copolymers (SVP). The adhesion strength between poly (styrene-co-acrylic acid) copolymers (SAA) and both metals increased at lower acrylic acid (AA) contents in the copolymers, but the adhesion strength remained almost unchanged at higher AA contents due to competition between interaction of free carboxylic acid with metal and self-association of acrylic acid units in the copolymer through dimerization of carboxylic acids. From the reflection-absorption infrared (RAIR) spectroscopy, it is concluded that the enhancement of adhesion strength by the incorporation of comonomers is caused by specific interaction between the copolymers and metals and orientation behavior of carbonyl groups in AA units and pyridine rings in VP units to the metal surfaces.

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Morphology on the 75/25 polyamide 6 (PA6)/polycarbonate (PC) blends with various ratios of maleic anhydride functionalized poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS-gMA) to poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was investigated by transmission electron microscopy, differential scanning calorimetry and small angle X-ray scattering. The total amount of added SEBS-gMA and SEBS was held constant at 20 parts hundred resin, (phr) i.e. 20 g against 100 g of the total amount of PA6 and PC). The 75/25 PA/PC blend with 0/20 SEBS-gMA/SEBS showed a co-continuous phase structure. The co-continuous phase morphology is one of the hallmarks of spinodal decomposition (SD), which takes place in the partially miscible system. It has been known that a binary blend of PA6/PC is completely immiscible at all temperatures. In contrast, the 75/25 PA/PC blends with 5/15, 10/10 and 20/0 SEBS-gMA/SEBS showed dispersed PC macrodomains and SEBS/SEBS-gMA microdomains in the PA6 matrix, indicating that these blends are totally immiscible. On blending with 0/20 SEBS-gMA/SEBS, the PA6 crystallinity and crystallization temperature (Tc) were lower than in other blends and the periodic regularity of SEBS-gMA/SEBS microphase separation was higher. In the other blends, the crystallinity and Tc was high and the periodic regularity of SEBS-gMA/SEBS microphase separation was low. This behavior is believed to arise from the different phase morphology formed on changing the ratio of SEBS-gMA to SEBS.

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Blends of chitosan with polyamide 6 (PA6) were prepared via the solution casting technique using formic acid as a common solvent. The morphology and the mechanical behaviour of films with chitosan concentrations ranging from 15% to 70% (w/w) were investigated by scanning electron microscopy and dynamic mechanical analysis. Assuming an hypothesis about blend morphology, the mechanical behaviour of the materials was predicted from various models involving the percolation concept. From comparison between experimental and predicted data it is concluded that the chitosan phase tends to sediment and to form a continuous phase on the lower face of the film, if the chitosan content is high enough. This continuous phase is bristling with chitosan domain cones, which can emerge on the upper face of the film depending on the blend composition. The PA6 rich domains fill the upper face of the sample.

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A rotational isomeric state (RIS) model for polymeric sulfur chains has been used to calculate the concentrations of cyclics Sx with x ⬎ 8 in liquid sulfur below the critical polymerization temperature. The cyclics S12, S18 and S20 were predicted to be present in the largest amounts in agreement with experiment. Other cyclics such as S11 and S13 were predicted to be absent from the melt and they are known to be physically present in only trace amounts. Variations of structural and statistical weight parameters in the RIS model are explored. The original model is shown to give the best agreement with all experimental information.

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In order to improve the stability of high density polyethylene (HDPE) as a thermal energy storage medium, HDPE was cross-linked by electron beam irradiation. Solid state NMR spectroscopic methods were used to analyze the cross-linked HDPE and its thermal degradation. The influence of ethylene glycol (EG) as a heat transfer fluid on the cross-linked HDPE was also investigated. Neither oxidation nor phase transition was observed in HDPE kept in vacuum, even after 1000 h at 1508C. However, both phenomena were observed in HDPE either kept at 1508C or thermally cycled in air. HDPE completely immersed in EG was not oxidized, but phase transition from crystalline to amorphous, probably caused by the penetration of EG into the HDPE, was detected. The observed increase of amorphous phase was attributed to a result of crystalline to amorphous phase transition of perturbed regions in the crystalline phase close to defect sites occupied by oxidation products or EG molecules.

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Solid state 13 C n.m.r. measurements were carried out on polymer networks based on methyl methacrylate and diethylene-glycol–bis-allylcarbonate. Several relaxation time parameters (rotating frame and laboratory frame proton and carbon relaxation times) were determined. Cross-polarisation times and carbon relaxation times were interpreted based on the changes in the molecular motion during the curing process. Proton relaxation times were interpreted based on the heterogeneity of the matrix. Results confirmed phase separation at complete conversion.

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