1994 рік

The interaction between drugs (indomethacin (ID), p-chlorobenzamide (CBA) and 5-methoxy-2-methyl-3- indoleacetic acid (MMI)) and bovine serum albumin (BSA) was investigated by equilibrium dialysis and nuclear magnetic resonance (n.m.r.) spectroscopy. The binding of ID and MMI to BSA was concluded to be hydrophobic and hydrophilic, respectively, on the basis of the dependence of the binding constants on temperature and ionic strength. In 1H n.m.r, spectra of ID, there were no significant shifts with change in the concentration and on addition of BSA. The spin-lattice relaxation time (T1) and spin-spin relaxation time (Tz) of the respective protons of ID were independent of concentration, but depended on the concentration of BSA added. The binding position was determined from the ratio of the spin-spin relaxation rates of ID bound to BSA and free ID. ID and MMI were found to bind to BSA through the aromatic moiety and the carboxyl group as the substituent, respectively. The binding property of ID was known to be governed by the competition between the hydrophobic effect of the chlorophenyl group and the hydrophilic effect of the carboxyl group in the molecule

Детальніше...  

Samples of commercial nylon 7 were given different thermal or precipitation histories. Structure and crystallinity were followed by d.s.c., solid-state n.m.r, and attenuated total reflectance Fourier transform infra-red spectroscopy (ATR FTi.r.). Heat of fusion and melting temperature values ranged from 52 to 93 J g-1 and 228 to 242°C, respectively. Surprisingly, annealing did not give material with the greatest heat of fusion although it possessed the highest melting point. Solid-state 13C and z 5 N n.m.r, methods were used to observe the amorphous and crystalline fractions. For example, the amide nitrogens show resonances near 86.5ppm in amorphous domains, near 84ppm in or-crystals and near 89ppm in y-crystals, lSN cross-polarization/magic angle spinning spectra of solution cast samples contained peaks consistent with all three domains in various intensity ratios but with the y-peak being the most intense for most samples. Solid-state 13 C spectra contained peaks which supported the presence of these phases but with the or-phase peaks predominating. Treatment of solution-cast thin films with aqueous KI/I2 gave materials whose n.m.r. spectra contained peaks consistent with these three phases in different ratios than for the initial solution-cast samples. Spectra of the melt crystallized samples contained peaks for amorphous and s-domains only. 13C spin-lattice relaxation (T~) magnetization decays could be fit to two or three exponentials (Tls of hundreds of milliseconds, a few seconds and hundreds of seconds) consistent with semicrystalline polymer behaviour. T~ values for the long-relaxing component ranged from 350 to 23 s for the annealed and precipitated samples, respectively. Amide V bands near 682 cm-1, assigned previously to the or-phase, were present in the ATR FTi.r. spectra of all the samples. However, the chemically treated and solution cast samples contained additional bands at 690 and 620 cm- 1 due to the y-phase. Spectra of quenched samples contained bands not seen in the other spectra

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A model procedure has been proposed to predict the yield strength of binary blends of thermoplastics on the basis of the information on the continuity of phases acquired from the Hill model for the elastic properties of two-component systems. Utilizing this information in an equivalent box model and assuming either 'perfect' or 'zero' interracial adhesion, the upper and lower bounds of the yield strength can be calculated. The upper bound may be close to (but lower than) the dependence corresponding to the additivity (rule of mixtures). The lower bound passes through a minimum at a composition of about 50/50 (by volume), which corresponds to the phase-inversion point in the Hill model. The minimum yield strength is linked to the minimum of the sum of the continuity parameters of the components in the blends. Predicted dependences of the yield strength on the blend composition are in reasonable accord with the experimental data for blends with good or poor interfacial adhesion. If the model is to be employed for the appraisal of the interracial adhesion in polymer blends, other factors affecting the phase structure should be taken into account, e.g. relative melt viscosities, particle size, orientation during processing, cavitation, etc.

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Successful attempts to produce high-molecular-weight polyanilines via electrochemical synthesis are reported. A systematic study of the influence of electropolymerization conditions on the weight-average molecular weight (Mw) showed that Mw of polyaniline varied only between about 22 000 and 40 000 g mol- 1, even for a wide range of conditions. Significant increases in Mw are only obtained when a neutral salt is added to the electrolyte. Mw can be increased up to 160 000 g tool-1 by increasing the LiC1 concentration to about 6 M. This salt effect on M, is consistent with electrostatic charge screening effects.

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The structures of the Pruitt-Baggett adduct (PBA) and the Pruitt-Baggett catalyst (PBC) were studied in some detail. PBC extensively ionizes in acetonitrile (K d = 3.48 x l0 3 mol 1 1 at 25°C) producing an anionic fragment composed of seven Fe atoms and a cationic fragment with two Fe atoms. Hittorf electrolysis showed that the anionic fragments exclusively bore the high molecular weight stereoregular poly(propylene oxide)s (K-polymers). However, study of the polymerization in the presence of anion and cation scavengers and in different dielectric media supported a previous conclusion that neither free anions nor cations were solely responsible for the stereoregular polymerization, but together with a monomer molecule they combine to yield catalytically active monomer-bound ion pairs. The study of the product showed that K-polymers were connected to each other with Fe atoms. However, these chains could be freed by extracting the Fe residues with hydrochloric acid. A mechanism for the stereoregular polymerization of propylene oxide that is consistent with the present and already published data was suggested

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The structures of microbial cellulose-fluorescent brightener complexes, produced from the Acetobacter culture in the presence of a fluorescent brightener, and the cellulose samples regenerated from them have been examined by cross-polarization/magic-angle spinning (c.p./m.a.s.) 13C n.m.r, spectroscopy. C4 and C6 resonance lines for the cellulose components of the complexes appear at about 84.0 and 63.0 ppm, respectively, with the disappearance of their downfield crystalline components. Since the chemical shifts of the lines are in good accord with those of the non-crystalline component of native cellulose, it is concluded that the cellulose component of the complex is in the non-crystalline state. ~3C spin-lattice relaxation time (Tic) measurements have also confirmed that the Tic values of the dried complexes are of the same order as those for the non-crystalline component of native cellulose. In contrast, the T~c values of the non-dried complex are much shorter than those of the dried complexes, indicating a much enhanced molecular mobility in the non-dried complex. On the other hand, when the non-dried complex is subjected to dye extraction, C4 and C6 resonance lines assignable to the crystalline component can be observed in the c.p./m.a.s, spectrum. Moreover, selective measurements of the spectrum of the crystalline component have revealed that cellulose Ifl is preferentially grown from the non-dried complex by dye extraction. In the case of the dried complexes, only very small amounts of cellulose I crystals are regenerated, possibly as a result of the formation of tight hydrogen bonds in the complex.

Детальніше...  

The oscillatory behaviour of neck propagation during cold drawing of polymer films has been studied numerically. Previous calculations based on Barenblatt's model considering the temperature rise at the neck have been refined by introducing heat diffusion and the consequent temperature distribution in the film. Period doubling of the oscillation and other phenomena that were observed experimentally and remained to be explained have been produced by the refined model

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Copolymers containing diethylsiloxane and functional siloxane groups of the form RR'SiO (where R, R'= phenyl, and R = methyl, R'= 3,3,3-trifluoropropyl) were synthesized by equilibrium polymerization of the appropriate cyclotrisiloxanes in the presence of KOH. Quantitative 29Si n.m.r, spectroscopy indicated that the copolymers possessed random microstructures. D.s.c. and dynamic mechanical analysis show that both substituents are effective in lowering the crystal melting and low-temperature crystal-crystal transitions with respect to the diethylsiloxane homopolymer, and ultimately lead to non-crystalline copolymers.

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Suspension poly(vinyl chloride) (PVC) samples with various monomer conversions were synthesized using batch and semi-batch polymerization processes at different temperatures. The concentration of tertiary chlorines in the PVC was determined using 13C nuclear magnetic resonance, and the concentration of internal double bonds was analysed by ozonolysis. The dehydrochlorination rate of the PVC was measured at 190°C by the conductimetric method under nitrogen environment. It was found that the concentration of tertiary chlorines increases significantly with increase in monomer conversion after the critical conversion at which the reactor pressure starts to fall. At the same conversion level, it increases with polymerization temperature. The concentration of allylic chlorines is much lower than that of tertiary chlorines. A conversion dependence of allylic chlorines was not found for the present PVC samples. However, the concentration of allylic chlorines increases with polymerization temperature. Excellent correlation between the dehydrochlorination rate and the concentration of tertiary chlorines was found based on the present experimental data, but no significant relationship was found between dehydrochlorination rate and concentration of allylic chlorines. Therefore, tertiary chlorines in PVC chains are probably the defect structure that is most responsible for the reduced thermal stability of PVC. The mechanisms of formation of internal defect structures and the effects of polymerization conditions on the concentration of the defect structures are discussed in some detail based on diffusion-controlled free-radical polymerization theory, and the monomer concentration effects are further confirmed by the results using a semi-batch polymerization process. The concentration of tertiary chlorines can be minimized by semi-batch operation at or near the saturation pressure, providing PVC of higher thermal stability

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The opto-mechanical behaviour of a rigid diacetylene-containing segmented copolyurethane has been investigated in detail by using Raman spectroscopy. Experiments were carried out to determine the tensile and compressive strain dependence of the Raman frequency of the C::x---C triple bond stretching mode in the copolymer. A similar initial strain-induced frequency shift of 4.7 + 0.5 cm- 1/% strain was found in both tensile and compression tests. Angular strains were measured by obtaining the Raman spectra of the copolymer at different angles of the laser beam polarization with respect to the principal tensile axis, and it was found that the experimental results are in general agreement with classical elasticity theory, although they differ in detail. The molecular deformation of the polydiacetylene moieties in the copolymer has also been discussed.

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