1994 рік

The transport of pharmaceuticals through silk fibroin membranes has been investigated. The membrane was prepared from Chinese cocoon. The permeability coefficients of five kinds of pharmaceutical, i.e. 5-fluorouracil (5FU), L-( + )-ascorbic acid (Vc), resorcinol (Res), sodium phenolsulfonate (SPS) and benzyltrimethylammonium chloride (BTAC), were measured in the pH range from 3.0 to 9.0. The silk fibroin membrane was an amphoteric ion-exchange membrane composed of both weak acidic and weak basic groups. Membrane-potential measurements revealed that the isoelectric point of the membrane was about pH 4.5. The positively charged pharmaceutical, BTAC, was excluded from the membrane below the isoelectric point. On the other hand, the negatively charged one, SPS, had a permeability that decreased as the pH increased. The neutral molecule, Res, however, penetrated through the membrane independently of pH value over the measured pH range. In the case of 5FU and Vc, the permeability coefficients decreased steeply above pH 7 and pH 4, respectively, because 5FU and Vc were negatively charged above pH 7 (pKa = 8.0) and pH 4 (pKa = 4.25), respectively

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Conformations in chains of poly(ethylene terephthalate) (PET) have been studied by using the molecular orbital package, Mopac, and the molecular modelling package, Polygraf. Both methods reveal two stable structures, namely one where the molecule is planar, and the other in which the CO-O-C-C dihedrals are rotated to ~ +__ 80 °. These correspond to the well known triclinic crystal structure of PET and a new observed mesophase. Various methods were used to predict the moduli of such chains, both as isolated chains and in a crystal structure. A qualitative agreement with the experimental moduli was found.

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The fluorescence spectrum of 1-(4-dimethyIaminophenyl)-6-phenyl-1,3,5-hexatriene (DMA-DPH) dissolved in a stoichiometric mixture of diglycidyl ether of bisphenol A and diethylene triamine was measured as a function of cure time at various cure temperatures. The frequency of the fluorescence maximum for DMA-DPH increased during the curing reactions because of the change in the polarity of the epoxy resin. In an isothermal cure, the fluorescence frequency increased linearly with the cure time until the gelation occurred. The total change in fluorescence frequency that occurred from the beginning of the isothermal cure to the gelation time was 1000 cm- ~ and was independent of the cure temperature, implying that the chemical structure of the infinite network at the gelation time was independent of the cure temperature. The rate constant, Kx, for the polarity change during an isothermal cure of the epoxy resin, defined as the rate constant for the linear increase in fluorescence frequency, was determined. The activation energy of KT was estimated to be 60 kJ mol-1.

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Polybutadiene polyepoxide, the product of the catalytic reaction of cis-polybutadiene with chloromanganese( Ill) teraphenylporphyrin in association with iodosylbenzene, was converted to polyalcohol and polyether when treated with anhydrous oxalic acid and acidified water, respectively

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The effects of several different compatibilizing agents with reactive functional groups (acid and/or anhydride) on the morphology of blends of styrene-acrylonitrile copolymers (SAN) in polyamide (PA) matrices were investigated using transmission electron microscopy. The primary focus was on the use of a series of imidized acrylic polymers and how their functionality for reaction with nylon-6 and their miscibility with SAN copolymers affected the morphology of nylon-6/SAN blends. Glass transition behaviour of binary blends of the imidized acrylic polymers with SAN systems indicated that miscible blends over a restricted range of AN content in the SAN could be obtained by limiting the imide and free-acid contents of the imidized acrylic polymers. In the case of the ternary polyamide blends, the most efficient reduction in the dispersed-phase particle size was obtained via imidized acrylic polymers that are miscible with the SAN phase and can react with the polyimide to a significant degree. For nylon-6/SAN blends compatibilized with polymers containing a high level of anhydride functionality, complex morphologies consisting of at least two distinct populations of dispersed phase were observed. The factors responsible for generation of such complex morphologies were examined using different staining techniques, and it was proposed that a rheological effect is the dominant issue. The chemical functionality characteristics of the polyamide matrix were also shown to have an effect on the morphology of nylon/SAN blends compatibilized with imidized acrylic polymers.

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In this paper, we outline the photochemical and spectroscopic properties of a new class of light-sensitive polymers obtained as a result of poly(styrene-co-2-bromoethyl methacrylate) and chloromethylated polystyrene modification by attaching a pendent hydroxycinnamate group. These specific cinnamates after addition of tertiary amine display characteristic dual fluorescence. Dual emission is attributed to the presence of two different forms of phenol group. Analysis of the kinetic data of the formation of the ionized form indicates a substantial difference between the polymeric and monomeric systems. Simultaneously, the addition of tertiary amine causes quenching of the singlet excited state. As a result, a sharp decrease in the sensitivity is observed. It is also shown that hydroxycinnamates are sensitive in both the neutral and ionized forms of the light-sensitive group. Based on experiments, a kinetic scheme for the processes taking place during irradiation is proposed.

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The kinetics of emulsion polymerization of vinyl propionate (VP) using the redox system potassium persulfate (KPS)/acetone-sodium bisulfite (ASBS) as redox pair initiation system is studied at 25°C. The effect of different initiator concentrations on the rate of polymerization and on the number and size of particles of the formed emulsion latices is established. The polymerization proceeded smoothly till high conversion and yielded stable emulsion latices. The rate of polymerization was found to be dependent on the initiator concentration to the 2/5 power.

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Phase structures of nylon-11/polyepichlorohydrin (Ny-11/PECH) blends are studied by nuclear magnetic resonance, differential scanning calorimetry and transmission electron microscopy techniques. In the solid state, although the domain size of these mechanical blends is 1-2 pm, blending does change the motional states/phase structures of the two components. The motional freedom of PECH chains decreases as the composition of Ny-11 increases in the blends. The amorphous phase of Ny-11 changes less after blending, but increasing PECH in the blends causes the crystalline phase ofNy-11 to be disordered and the crystallinity of Ny-11 component to decrease. When the blend is PECH-rich, the crystalline phase of Ny-11 component disappears. The two-dimensional nuclear Overhauser effect result indicates that there are intermolecular interactions between Ny-11 and linear PECH chains, and the system is miscible in dimethylsulfoxide solution.

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Morphological studies have been carried out in detail by means of differential scanning calorimetry, polarizing and scanning electron microscopies, small-angle light scattering, X-ray diffraction, infra-red spectroscopy and refractive-index measurements for oriented specimens of thermotropic liquid-crystalline polyesters with so-called two-dimensional mesogenic units along the polymer chains, which were synthesized by solution polycondensation of the monomers 4,4'-(alkylene dioyldioxy)dibenzoyl dichloride and 2,5-dihydroxyl-l,4-phenylene di-p-alkyloxybenzoate at low temperatures. All the studied polyesters, designated respectively as P(2,6), P(2,8) and P(5,8), were found to exhibit nematic liquid-crystalline behaviour above their melting points. Mat-like or banded textures have been observed in oriented films of these specimens, which were prepared by shearing in the mesomorphic state and subsequent quenching to room temperature. More regular and perfect bands were exhibited in specimen P(2,8) than in P(5,8) and P(2,6), and their average bandwidths evaluated optically were around 6, 8 and 12 pm, respectively. These three specimens had different molecular weights, and such differences were found to influence strongly the features and ease of formation of the banded structure: the bandwidth was decreased and band quality was improved with increasing molecular weight. Furthermore, bandwidth could also be changed sensitively on varying the shearing rate during preparation of oriented specimens. In the case of P(2,8), the orientation direction of fibrils aggregated by polymer chains was found to deviate from the shearing direction alternately by a deviation angle of about ___ 30 °, on going from band to band. Based on the scanning electron microscope observations and X-ray diffraction data, it was understood that the zigzag planes of oriented fibrils, which have average diameter ranging from 50 to 100 nm, are parallel or nearly parallel to the specimen surface, and they are stacked layer-like along the specimen thickness direction. Moreover, it was suggested from the three-dimensional infra-red spectra and refractive-index data that the planes including the intersected X-shaped mesogens may be oriented parallel or nearly parallel to the zigzag plane or film surface, and all the phenylene rings tend to orient their planes parallel to the zigzag plane as a whole. The banded texture and its interior structure were found to be quite thermally stable even at temperatures somewhat higher than the isotropization point of the unoriented polymer, suggesting that the thermal motions of individual polymer chains are severely limited and do not easily destroy the fibrillar structure and other supermolecular structures formed in the process of preparing oriented films.

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Styrene (S)-isoprene (I) star-shaped block copolymers of the (SI)4 and (SI)l 2 types were prepared by an anionic polymerization technique. Linear SI arm molecules were prepared with sec-butyilithium as an initiator in benzene, followed by a coupling reaction with the 4-functional linking agent 1,2-bis(methyldichlorosilyl) ethane and the 12-functional 1,1,2,2-tetrakis(2-(trichlorosilyl)ethyl)silane, respectively, under vacuum. The star-shaped block copolymers were isolated by precipitational fractionation from aspolymerized crude products using benzene-methanol mixtures. They were confirmed to have the designed molecular structures by careful characterization. Using a transmission electron microscope it was observed that the microphase-separated structures of solvent-cast films of the samples are polystyrene (PS) cylinders in a polyisoprene (PI) matrix, alternating lametlar structures and PI cylinders in a PS matrix for 4-armed star-shaped block copolymers when the values of the volume fraction of PS, q~s, are 0.23, 0.47 and 0.78, respectively, and lamellar structures for the 12-armed star-shaped block copolymers when the q~s values are ~0.5. Small-angle X-ray scattering studies revealed that lamellar domain spacings of the star-shaped block copolymers are essentially the same as those of the arm molecules, that is, linear diblock copolymers, irrespective of the number of arms.

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