1993 рік

A mutant strain of Acetobacter xylinum was isolated, which produces cellulose of anomalous band-like morphology in contrast to straight, crystalline microfibrils of cellulose I normally produced by the wild-type strain. The band material extruded perpendicularly from the cell surface constitutes strand-like structures with lateral dimensions of 10 nm. Electron diffraction analysis revealed that these strands are composed of cellulose II crystallites within which the molecular chains are oriented perpendicular to the strand axis. Because the average length of glucan chains in this material was determined to be about 10 times the width of the 10 nm wide strand, the elucidated features make it highly likely that this form of cellulose II involves chain folding which gives rise to the antiparallel structure

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A means of generating high temperature polymer foams with pore sizes in the nanometre range has been developed. Foams were prepared by casting block copolymers comprising a thermally stable block as the matrix and a thermally labile material as the dispersed phase. Upon thermal treatment the thermally unstable block underwent thermolysis, leaving pores with a size and shape dictated by the initial copolymer morphology. Nanopore foam formation is shown for triblock copolymers composed of a poly(phenylquinoxaline) (PPQ) matrix with either poly(propylene oxide) (PO) or poly(methyl methacrylate) (PMMA) as the thermally labile coblocks. Upon decomposition of these blocks, a 10-20% reduction in density was observed, consistent with the initial PO or PMMA composition, and the resulting PPQ foams showed dielectric constants of about 2.4, substantially lower than that of PPQ (2.8). Small-angle X-ray scattering and transmission electron microscopy showed pore sizes of approximately 100 A

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The synthesis and characterization of a series of crown ether 'comb-branch' polymers is reported wherein [12]- and [14]-ring lithium binding units have been linked to a polyacrylate or polymethacrylate backbone via a simple ester link or a C6 or oxydiethylene chain. Preliminary data on glass transition temperature, Tg, and conductivity reveal a relative insensitivity of T~ to added lithium in the [14] series and higher conductivities in the [12]-O 4 series

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This paper presents a new synthetic polycarboxylic compound, i.e. a benzocaine-modified maleic anhydride-cyclohexyl-l,3-dioxepin copolymer, p-Aminobenzoic acid is linked via an anaesthesine (p-aminoethylbenzoate, benzocaine) to the carboxylic groups of the copolymer, both as a spacer and to increase the hydrophobicity of the polymer through the phenyl group. The structure of the modified copolymer is characterized by thin-layer chromatography and by i.r. and n.m.r, spectroscopy

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Slow crack growth was measured in three polyethylene copolymers by a notch tensile test at 50°C in Igepal Co-630. The concentration of Igepal was varied from 0 to 100%. The largest reduction in time to failure occurred in the concentration range between 0% and 0.1%. From 0.1 to 20% concentration, the additional effect was much less. A minimum in time to failure occurred at ~ 50% concentration. There is a significant increase in failure time when the concentration is increased from 50 to 100%. If the failure time is < 103 min in air, Igepal has practically no effect

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The arylpropargyl-ether-terminated monomer (1,4-HC::::x---CCH2OCrH4)2CMe2 was polymerized to just before the gel point in the presence of various catalysts. Changes in the IH n.m.r, spectra show that (a) (r/-Cp)Co(CO)2 gives rise exclusively to acetylene cyclotrimerization, (b) (r/-Cp)2Ni and (PPh3)2NiCI 2 each result in both cyclotrimerization and non-aromatic polyene formation, and (c) (PPh3)3RhCI gives branched eneyne dimers.

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The synthesis of a polydimethylsiloxane chain with a random distribution of deuterated and non-deuterated methyl groups is described. Cationic polymerization provides an excellent mechanism for statistical sequencing. The test for randomness is given by a neutron scattering experiment on a semidilute solution. In the reciprocal interval (1 x 10-2 A-1, 1 x 10-1 .~-1), the response is uniformly devoid of any copolymer correlation effect. A totally furtive chain can thus be inserted in a polymer solution, at zero average contrast between deuterated and non-deuterated chains.

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The mechanical strength of oriented and non-oriented polypropylene films was studied at a deformation rate of 50 mm min- 1 and room temperature by using a statistical method. For the oriented and non-oriented films, the numbers of discrete strength levels were found to be eight and nine, respectively. The discrete strength levels were attributed to the spectra of the defects in the form of submicro-, micro- and macrocrazes. Oriented films showed higher levels of mechanical strength -- an effect attributed to the absence of macrocrazes

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~-Hydroxy-co-carboxy-poly(methyl methacrylate) was prepared by anionic polymerization with an initiator obtained by the reaction between 1-[4-(2-tert-butyldimethylsiloxy)-ethyl]phenyl-l-phenylethylene and n-butyllithium, followed by termination with carbon dioxide and hydrolysis of tert-butyldimethylsilyl ether. The resulting polymer was found to be pure and to have a fairly narrow molecular weight distribution.

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In this study the polymerization of monomer-containing micro-emulsions to yield porous polymeric membranes is demonstrated. A micro-emulsion system composed of methyl methacrylate and acrylic acid as monomers, ethyleneglycol dimethacrylate as crosslinking agent, sodium dodecylsulfate as surfactant and water was studied. An identical surfactant-free system, formed using the same monomers, crosslinking agent and water but without surfactant, was also studied and the micro-emulsions formed at certain compositions were polymerized. Our earlier work with these systems had indicated the porous morphology of the polymer to be dependent on the microstructure of the precursor micro-emulsion. In the present study micro-emulsion compositions which showed inferential evidence of a bicontinuous structure were polymerized to form membranes by using photo-initiated polymerization with ultra-violet radiation. The membranes formed had a thickness of 10-12/~m. The swelling characteristics in water of the polymeric material constituting the membranes was evaluated as a function of pH. The tensile properties of the membranes were also evaluated. The permeability of the membranes was examined using aqueous solutions of acrylic acid. The results indicate the permeability of the membranes to be dependent on the composition of the precursor micro-emulsion due to the relationship between the polymer morphology and micro-emulsion structure. This study conclusively shows the feasibility of synthesizing porous polymeric membranes by utilizing the structure of micro-emulsions.

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