1993 рік

Non-linear pattern formation in polymer systems has been studied. We present the undulation pattern observed on the free surface of a polymer film cast from solution, for poly (styrene-ran-butadiene) random copolymer and for mixtures of polystyrene and dioctyiphthalate. The undulation pattern was similar to a hexagonal cellular pattern observed for low viscous fluid produced by Rayleigh-Brnard convection. It was considered that steady-state convective flows occur in a polymer solution with relatively low viscosity, which is induced by solvent evaporation in the earlier stage of casting. Inhomogeneity of the polymer concentration attributed to the convection was considered to play an important role in the pattern formation

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Electrochemical polymerization of 4-(3-pyrrolyl)-4-oxobutyric acid and its copolymerization with pyrrole produces electroactive polymers and copolymers, respectively. This study highlights the advantages to be gained by using transient potential waveforms for production of polymer materials

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The contact angles of poly(2-ethylhexyl acrylate-co-acrylic acid) (P(2EHA-AA)) with organic liquids, such as dispersion, polar and hydrogen bonding liquids, were investigated. The contact angle 0 of organic liquids on P(2EHA-AA) decreased exponentially with contact time t, i.e. log 0 = - K log t. It was suggested that the proportional constant K was influenced by the liquid's surface tension 7L, viscosity and glass transition temperature of P(2EHA-AA).

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Melt-extruded polypropylene resin containing 1% or 2% ceresine wax yielded thin films that had significantly increased dielectric breakdown strengths but with virtually identical bulk dielectric properties. Ceresine wax acts as a trapping centre for electrons and by minimizing ionization of host polypropylene molecules, dielectric breakdown strength is increased.

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X-ray diffraction, Fourier Transform infra-red (FTi.r.) spectroscopic and refractive index measurements have been utilized to characterize the state of molecular orientation in one-way and two-way (biaxially) drawn isotactic polypropylene (iPP) films. It is shown that the use of all three techniques leads to much greater confidence in the orientation averages deduced than can be obtained by using any two of the techniques. Orientation parameters in terms of (cos 2 0) values in machine, transverse and normal directions have been evaluated and compared quantitatively for the different techniques. The results indicate that with one-way drawing the chain axes of both crystalline and amorphous regions orient towards the direction of drawing. The crystalline chains are more highly oriented than the amorphous chains and tend to orient towards the plane of the film, whereas the amorphous chains tend to be more uniaxially oriented towards the draw direction. In balanced, simultaneously two-way drawn films the crystalline chains are more highly oriented towards the plane of the film than the non-crystalline chains. For a sequentially, equibiaxially drawn iPP film, the orientations of the chain axes of both the crystalline and amorphous regions were found to be higher in the second draw (i.e. transverse) direction than in the first draw direction. The orientation of the crystalline chains was very close to the plane of the film, whereas the amorphous chains were almost uniaxially oriented with respect to the second draw direction. In all the films there is a strong tendency for the b-axes of the crystallites to align normal to the plane of the film.

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The reactions taking place during melt mixing of polyarylate (a copolyester of bisphenol A and an equimolar mixture of isophthalic and terephthalic acids) with poly(butylene terephthalate) (PBT) were studied by 1H and 13C nuclear magnetic resonance (n.m.r.). Model compounds whose structures match those of the polymers and possible interchange units were synthesized and characterized by 1H and 13C n.m.r. By means of this characterization, assignments of the absorptions appearing in the spectra of the soluble fraction were possible.

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Thin films of polypyrrole doped with polymeric nickel phthalocyanine were grown on a platinum substrate by the electrochemical oxidation of pyrrole from aqueous solution containing 0.01 M pyrrole and 0.1 M sodium salt of polymeric nickel phthalocyanine as the only supporting electrolyte. The film thus prepared was characterized by i.r., u.v.-vis., e.s.c.a, and by conductivity measurements. The electrochemical behaviour of the electrode was studied by cyclic voltammetry in aqueous and non-aqueous electrolytes. The film exhibits stable conductivity and reversible electrochemical behaviour in the range of the potential investigated

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The crystalline, conjugated polymer poly(2-methoxyphenylene vinylene) undergoes a solid-state thermochromic transition at about 350°C. The optical absorption maximum shifts hypochromicaily as the colour of the film changes from orange to olive-green during the transition. This effect can be correlated with an endothermic event, as seen in differential scanning calorimetric measurements. Polarized infra-red spectra reveal that movements of the phenylene rings about the chain axis are involved in the transition. The polymer deviates from the low-temperature rigid-rod planar structure during the transition, but conjugation is restored at temperatures above the transition. A molecular motion mechanism is proposed that involves phenylene ring wagging motion relative to the ring-ring axis as the temperature increases. At the transition temperature, the rings undergo a 180 ° flip about the chain axis. This motion causes a temporary and reversible decrease of effective conjugation along the backbone of the polymer, and the colour change is interpreted as a consequence of such phenylene ring motions.

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The reaction of cellulose with acryloyl chloride in LiCl/N,N-dimethyl acetamide resulted in a water soluble cellulose acrylate. The degree of substitution per anhydroglucose unit was determined from the titration of the double bond with bromine. Crosslinking of the acryloyl moieties was carried out in aqueous solution using K2S208/FeSO4 as redox initiator. The original cellulose, cellulose acrylate and the crosslinked cellulose acrylate were characterized by i.r., wide-angle X-ray diffraction, d.s.c., t.g.a, and solid state 13C n.m.r. Crosslinked cellulose is insoluble in water and the gel fraction was measured with a Soxhlet extractor. The fundamental properties of the crosslinked cellulose acrylate films were evaluated. Experimental results indicated that this water soluble and crosslinkable cellulose acrylate is a promising candidate as a water-borne coating material

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The application of selective ozonolysis together with high-resolution g.p.c, was performed to determine the crystalline stem lengths, in monomer units, of chain-folded lamellar crystals for trans and cis polyisoprene and polybutadiene. The trans polymer crystals were crystallized at -20°C in hexane directly from the dissolution temperature of 60°C, while the cis polymer crystals were crystallized by the same method at -70°C. The stem lengths of the trans- and cis-l,4-polyisoprene crystals were found to be 11 and 10 monomer units, respectively. Those for trans- and cis-l,4-polybutadiene crystals were found to be 12 and 13 monomer units, respectively

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