1999 рік

Inherent viscosities were measured for polystyrene (PS) in N,N-dimethylformamide (DMF)/cyclohexane (CH) in the temperature range covered from 65°C close to the upper critical solution temperature T C of the DMF/CH system. It was found that near the critical temperature, the inherent viscosities contracted to about one-third of the value at 65°C. The overall contraction behavior agrees well with de Gennes’ theory and some interesting results have been observed. First, in the far off-critical temperature range (logt ⬎ ¹ 1.5), the strong synergetic, co-solvency effect of the mixed solvent was shown by higher values of the inherent viscosity than those measured in any single solvent. Second, the reduced theta temperature, t v, at which the chain dimension was supposed to have the unperturbed, ideal dimension, weakly depends on the molecular weight. Third, although we observed only the contraction behavior instead of contraction-and-reswelling on approaching the critical point, the expansion factors a3h ( ¼ [h]=[h]v ) for the different molecular weight samples fell on one master curve when plotted as a function of (logt ¹ logtv )Mw1=2 . Here t[ ¼ (T ¹ TC )=TC ] and M w are the reduced temperature and the weight-average molecular weight, respectively.

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The interfacial structure of carbon fiber/polyetheretherketone (CF/PEEK) composites has been studied with Raman and X-ray photoelectron spectroscopy. Analysis of the fibers isolated from the composites proved that the polymer segments tended to form strong interactions with the fiber on the surface. Study of the fiber with a thin layer of PEEK coating further revealed that melting of the polymer plays an important role in forming the strong interfacial interaction. In connection with the above experimental results obtained from model systems with extremely low polymer content, the physical nature of the interfacial interaction is known through Raman spectroscopic observation of actual composites. Electronic matching between graphite crystallites of carbon fiber and the segments in special conformation is proved to be among the most important features of the intercalation-type interaction.

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Novel block copolymers were synthesised by a two-step chemical modification of polystyrene–polybutadiene block copolymer (PS-bPB). Such a modification includes hydrobromination or hydrosilylation of initial block copolymer and subsequent interaction of precursor with bidentate phosphine or phosphine oxide compounds. For interaction with the polymers, corresponding bidentate compounds were synthesised, which contained different amounts of carbon and silicon atoms between the phosphorus atoms. As both hydrobromination and hydrosilylation do not touch aromatic rings of polystyrene block, modification occurs solely in polybutadiene block.

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The presence of a small amount of an alkali cation in a magnesium solution dramatically increases the rate of defluorination of PTFE and enhances oxygenation. Evidence of this effect is observed for concentrations down to 1 mM and treatment durations of only 10 s. The presence of the alkali cation also makes the polymer porous. The rate of defluorination and the depth of attack increase both with the alkali cation concentration and with the duration of the treatment. Sodium is more reactive than potassium which is itself more reactive than lithium. The phenomenon is not limited to alkali cations and is also evident with the tetrabutylammonium cation. When nucleophiles such as diethylphosphite, thiophenoxide or the anions of 2-mercaptopyridine and thiourea are present in a solution of magnesium containing a moderate amount of solvated electrons ( < 50 mM), the grafting of the nucleophile to the polymer occurs but leads to poor yields.

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Macroscopic volume shrinkage and swelling of a poly(N-isopropylacrylamide), PNIPA, gel on heating was studied and the microscopic structural change during volume phase transition in water was correlated to variations of size, concentration and size distribution of free volume of the PNIPA gel estimated by positron annihilation lifetime measurement. An average free volume size of 0.28 nm radius of the swollen PNIPA gel coincided with that obtained in pure water below a transition temperature (33°C), whereas, in the collapsed state, two kinds of annihilation lifetimes of ortho-positronium were observed. This result implies that a nanoscopic phase separation occurs maybe because of the newly appeared free volumes of respective sizes, 0.18 nm and 0.33 nm in radius, by decreasing the motility of water molecules, accompanied with an aggregation of the polymer network and a significant expansion of the polymer network mesh size, although the macroscopic volume dramatically decreased. Nanoscopic inhomogeneity was discussed in terms of free volume size distribution. These results suggested that an inhomogeneity of the collapsed gel clearly differs from that of the swollen gel.

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An original laser-interferometric creep rate spectroscopy method was used for studying the molecular mobility in the glassy state of a series of 'model’ epoxy-amine networks varying in cross-link density and rigidity. The experiments were carried out over the temperature range 115–300 K, which covers the regions where the secondary relaxations are expected to occur. The creep rate spectra (CRS) obtained at low compressive stresses exhibited systematically multiple creep rate 1_ peaks, irrespective of the applied stress and the experimental time in the ranges under consideration, namely 20–40 MPa and 10–40 s, respectively. Data analysis was based on the inspection of the major peaks of the CRS without entering much into the details of the fine structure. The peaks assigned to the b relaxation were shown to depend on the changes in network cross-link density and to the addition of antiplasticizing molecules in the same way as reported earlier from dynamic mechanical analysis (DMA) and 13C nuclear magnetic resonance (NMR) studies. In the case of the resins cured with aromatic amines, for which no g relaxation is evidenced by DMA, creep rate spectroscopy allowed the detection of an additional relaxation, so called g 0 , at temperatures well below the b process. It was tentatively assigned to DMA-inactive motions of the aromatic amine residues, i.e. to the phenyl ring flips of the diphenylmethane units.

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The effect of iodine treatment on the uniaxial tensile drawing of an ethylene/vinyl-alcohol copolymer containing 44 mol% of ethylene units is studied as a function of draw temperature and iodine concentration. Drawing, between 60 and 100°C, of films soaked in a 0.125 M iodine solution involves complexation of the amorphous phase as judged from X-ray diffraction. The monoclinic crystalline phase turns into the mesomorphic form. Drawing films soaked in a 0.5 M solution brings about complexation of the crystalline phase in addition to the amorphous phase. Miyasaka’s model of substitution solid solution is assumed for the crystalline complex. It is suggested in addition that the mesomorphic form is a host structure for the complex. Drawing above 100°C involves segregation of molecular iodine accompanied by disruption of both the crystalline complex and the pure copolymer crystal. It is suggested that the polyiodides dissociate into molecular iodine which partly separates and crystallizes into pure domains and partly dissolves into the polymer crystals and breaks them down. Biaxial drawing of films soaked in 0.5 M solution has been carried out successfully at 90°C. Soaking into sodium thiosulfate solution removes iodine and regenerates a pure copolymer film in a biaxially oriented state.

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The rheological behaviour of polypropylene (PP)/acrylonitrile–butadiene rubber (NBR) blends has been investigated with special reference to the effect of blend ratio, compatibilization and dynamic vulcanization. The morphology of the extrudates and the size and distribution of domains were examined. PP/NBR blends show pseudoplastic behaviour, which is evidenced by the decrease in viscosity with increasing shear rate. The melt viscosity of these blends increased with increasing nitrile rubber concentration and shows negative deviation from the theoretically predicted values. Compatibilization of the blends with phenolic-modified polypropylene (Ph-PP) increases the melt viscosity at low concentrations of Ph-PP. The rheological behaviour of PP/BR blends was correlated with the blend morphology. Dynamic vulcanization has a decreasing effect on die swell values. The effect of temperature on the melt viscosity of the blends was examined and attempts have been made to construct a shear rate–temperature superposition master curve. The melt-flow index values for these blends were measured and have been correlated with rheometer data to develop a master curve for different blend compositions. The morphological analysis indicates that compatibilization of the blends prevents the coalescence of dispersed NBR domains during annealing.

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Films of 1:1 blend and films non-blended were prepared from poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) with a solution casting method, and the mechanical properties and morphology of the films were investigated using tensile tests, dynamic mechanical relaxation measurements, polarizing optical microscopy, differential scanning calorimetry (DSC) and X-ray diffractometry. The tensile strength, Young’s modulus, and the elongation-at-break of 1:1 blend films were found to be higher than those of non-blended films when their weight-average molecular weight (Mw) was in the range 1 × 10 5 –1 × 10 6. The enthalpy of melting for stereocomplex crystallites in 1:1 blend films was higher than that of homo-crystallites when Mw of polymers was below 2 × 10 5, while this relationship was reversed when MW increased to 1 × 10 6. Spherulites formation was suppressed in 1:1 blend films, whereas large-sized spherulites with radii of 100–1000 mm were formed for non-blended PLLA and PDLA films, irrespective of Mw. The mechanical properties of 1:1 blend films superior to those of non-blended films were ascribed to the micro-phase structure difference generated as a result of formation of many stereocomplex crystallites which acted as intermolecular cross-links during solvent evaporation of blend solution. On the contrary, non-blended films had larger-sized spherulites of less contacting area with the surrounding spherulites.

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The esterification reaction between the hydroxyl end groups in PET and trifluoroacetic acid on stirring at room temperature has been observed and studied. The reaction, which we refer to as end-capping, was found to be complete after 5 days. We demonstrate that whilst the reaction leads to modification of the end groups there is no significant degradation of the polymer chains. Proton nuclear magnetic resonance has been used to probe the kinetics of the reaction, and a pseudo first-order reaction rate constant of (7.8 ⫾ 1.8) х 10 ¹6 s ¹1 has been obtained. The results of this study may have implications for other polyester systems where strong acids are used as solvents.

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