1994 рік

The synthesis and first experiments on the rheological behaviour of poly(acrylamide) (PAAm) grafted with poly(ethylene oxide-co-propylene oxide) are presented. Well-defined, water-soluble graft copolymers were prepared in high yields by grafting poly(oxyalkylene) monoamines onto partly hydrolysed PAAm. Reversible gelation of aqueous graft copolymer solutions (c > c* = 1/[q]) was observed in 0.5 M K2COa at elevated temperatures, accompanied by viscosity changes of almost three orders of magnitude between 80 and 85°C at low shear rates. The observed phenomena are explained in terms of the formation of secondary bonds or association between the grafts

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The peel strength of laminated films comprising high-density polyethylene (HDPE) and blends of isotactic polypropylene (PP)/low-density polyethylene (LDPE) was studied as a function of the heat-treatment temperature, TH, the cooling condition, and the blend composition of the substrate films, where HDPE is the peel, i.e. the film to be peeled or the flexible adherend, and the blend is the substrate (the rigid adherend). The peel strength was strongly dependent on TH and the cooling rate. In the case of quenched films, the peel strength increased drastically for the films with T H higher than the melting temperature of PP, Tin,pp. For slowly cooled films, however, the peel strength had a maximum for films with Tn nearly equal to Tin,pp. By varying LDPE composition in the substrate, a systematic decrease in the peel strength was observed, indicating the important role of LDPE in the PP matrix in controlling the peel strength between HDPE and PP. The adhesion mechanism and the role of LDPE are discussed from the viewpoints of (1) partial miscibility and interdiffusion among PP, HDPE and LDPE, and (2) crystallization kinetics of the component polymers

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The general trend of equatorial and meridional small-angle X-ray scattering (SAXS) was investigated for four kinds of Kevlar fibres: regular Kevlar, Kevlar 49, Kevlar 149 and a heat-treated PPTA fibre, over a scattering angle 20 from 0.3 to 6.0 ° . Reflecting the fibre structure of highly oriented and extended chain conformation, the equatorial scattering is much more intensive and decreases in intensity more gradually with increasing scattering angle than the meridional scattering: i.e. the electron density fluctuations in the radial direction of the fibre due to interfibrillar and interstitial microvoids were expected to have Bragg spacings in the range from several to a few decades of angstroms, while no particular periodic fluctuation could be found in the fibre axis direction. The effects of total reflection upon the equatorial scattering intensity distribution were also discussed. The moisture sorption rate in a bone-dry regular Kevlar was observed at 25°C at saturated vapour pressure by the time-resolved SAXS technique. The experimental results were analysed assuming the moisture to be sorbed only in the microvoids to form various sizes of water cluster. Normalized moisture sorption rate, { 1 - [J(t)/J(O)] 1/2}/{ 1 - [J(oo)/J(0)'l 1/2}, determined from the change in integrated scattering intensity over the angular range 0.3-6.0 ° with time, J(t), was compared with that observed by a gravimetric method, M(t)/M(~), at a relative vapour pressure of 0.896 at 25°C. Although both rate curves attained equilibrium at almost the same time of about 670 min, the rate curve from the SAXS method showed a sigmoidal shape and the moisture diffusivity was much smaller than that determined from the gravimetric method. The large discrepancy between the two diffusivities was explained using the assumption that the gravimetric method detects the sorbed water in the form of both 'micro-water clusters' and 'macro-water clusters', but the SAXS method detects only the 'macro-water clusters'.

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Dextrans partially functionalized with chloroacetate groups were obtained by reaction of dextran with chloroacetyl chloride using pyridine as catalyst and the dimethylformamide/LiC! system as solvent. The structure of the resulting polymers was determined by means of infra-red, 1H and 13C nuclear magnetic resonance (n.m.r.) spectroscopy. ~3C n.m.r, spectra at 75.4MHz of partially modified dextran with chloroacetate groups were studied in order to evaluate the selectivity of the reaction of dextran with chloroacetyl chloride in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of the individual hydroxyl groups decreases in the order C2> C3 > C4. The coupling of model bioactive carboxylic acids (ct-naphthylacetic and 6-methoxy-~-2- naphthaleneacetic (naproxen)) to dextran functionalized with chloroacetate groups was carried out by reaction with their potassium salts or directly in the presence of 1,8-diazabicyclo[5.4.0]-7-undecene. High degrees of modification were obtained by both methods. However, the esterification reaction is somewhat more efficient in the case of the potassium salts

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From an analysis of the literature and our experimental results, we have established that interfacial tension is a function of the concentration of a compatibilizer, and put forward a 'three-stage' physical model to account for the compatibilizing behaviour of polymer blends. The effect of compatibilizer on size of the dispersed phase is studied in binary incompatible blends. The relation between the interfacial area occupied by each compatibilizer molecule and the concentration of the compatibilizer is also studied

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Overoxidation of polypyrrole was carried out electrochemically and studied by X-ray photoelectron spectroscopy. It is shown that overoxidation starts on the polymer adjacent to the electrode and then advances to the polymer facing solution. During overoxidation, original positive charges on polypyrrole (-NH ?-) are mostly replaced by -NH-, accompanied by the loss of counterions. Overoxidation progresses in two steps. Carbons are oxidized into C-OH in the first step and into C=O in the second step. Changing the pH of the media and increasing the potential have no significant effects on the degree of overoxidation in the range studied.

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The present paper describes the succinoylation of pullulan by reaction with succinic anhydride in dimethylsulfoxide as solvent and N,N'-dimethylaminopyridine as catalyst. Nuclear magnetic resonance analysis indicated that the carboxylic group is preferably introduced at the C-6 hydroxyl groups. A series of succinoylated pullulan derivatives are prepared with degrees of substitution ranging from 0 to 100%. Activation of the carboxylic groups with N,N'-carbonyldiimidazol and subsequent coupling with amines is discussed

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The hydrolytic degradation behaviour and some other properties were analysed for blends of microbial poly(3-hydroxybutyrate) [P(3HB)] with microbial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV); 3HV content, 22.3 mol%]. From the analysis of differential scanning calorimetry (d.s.c.) curves, the main component of the crystalline phase in the blend films was found to be P(3HB). The crystallinity of P(3HB) decreases on blending with P(3HB-co-3HV). The hydrolytic degradation of the blend films was carried out on the solution-cast films in phosphate buffer at 55°C and pH 7.4. The rate of hydrolytic degradation of the blend films was accelerated by blending with P(3HB-co-3HV), and showed linear correlation with crystallinity. Therefore, the degradation rate of P(3HB) can be controlled by blending with P(3HB-co-3HV). The lower the initial crystallinity of the blend films, the higher the rate of hydrolytic degradation is seen to be.

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The absence of any critical effects around c* in the diffusional behaviour of a range of molecular weights of narrow fraction polystyrene in tetrachloromethane has been re-examined. Analysis of the molecular weight dependent concentration coefficients kf of the concentration dependence shows sharp transitions between the dilute and semi-dilute behaviour. Spin-spin relaxation time measurements have also been performed and yield a value for c*. These values and other calculated and measured values are discussed in terms of the spectrum of motions present in a polymer system.

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The polymerization of styrene has been studied in ternary microemulsions which were stabilized by tetradecyltrimethylammonium bromide or octadecyltrimethylammonium chloride. The initiation of polymerization occurred mainly in the styrene-swollen microemulsion droplets, and the polymeric particles grew by recruiting monomer and surfactant from uninitiated droplets. The average hydrodynamic radius (Rh) of swollen particles first increased rapidly to a maximum at ~ 4 or 7% conversion, and then decreased slowly to a constant value. The variation in size follows the trend as simulated by a recent thermodynamic model. Due to the continuous nucleation, the number of polymer particles and the polydispersity of particle sizes increased continuously throughout the course of the polymerization process. The low average number of free radicals per particle (~<0.5) may be responsible for polystyrene with high molecular weights (Mw=6-11 x 106)

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