1992 рік

In order to explain the curved outline of some polymer crystals, we start from a slightly modified Frank's system of equations describing nucleation-controlled crystal growth. But we give an alternative and completely new interpretation of these equations with a view to applying them to the description of normal growth of crystals with rough surfaces. We show first that Mansfield's approximate solution of such equations is not exact, does not satisfy absorbing boundary conditions and does not depend on the rate of motion of these boundaries. Because that solution describes the facets of a crystal in terms of arcs of the same ellipse, it cannot be used to describe the curvature of 2 0 0 faces of those crystals of large elongation ratio which clearly are not parts of a single ellipse. The most puzzling feature of Mansfield's proposal is, however, that pronounced curvature is obtained solely if the mean distance between steps is assumed to be of the same order of magnitude as the width of a single stem. In such an eventuality, the use of the concept of nucleation-controlled growth becomes meaningless. We propose, therefore, a completely new interpretation of Frank's equations, which allows us to use these equations to describe nucleation-controlled growth. Then these equations appear as the mathematical formulation of a model that mediates between the approach of Seto and Frank, and that of Gilmer and Sadler. Detailed analysis of the experimental data, mostly those of Labaig and Bassett, shows that the outline of crystals with curved habit is neither elliptic nor made of elliptical arcs. We provide new and exact solutions of our generalized equations with generalized boundary conditions. These solutions account well for the experimental data. In some cases they may be approximated by Mansfield's solution (despite the fact that the change of curvature along the facets differs from that actually observed) or by the solution found independently by Toda and us (33th IUPAC Polymer Symposium at Montreal), despite the fact that it is unusual that near the tips of the crystals the outline of a crystal is well approximated by straight segments. The most important claim is, however, that our model appears as a bridge between the model of nucleation-controlled growth and that of normal growth of rough surfaces.

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Several electroactive n-conjugated polymers have recently shown promising non-linear optical (NLO) properties. However, long conjugation sequences in such polymers as polyacetylene (PA), polythiophene (PT), poly (p-phenylene vinylene ) (PPV) and poly (2,5-thienylene vinylene ) (PTV) often result in solubility, processability and optical transparency problems that make their use in electro-optic devices difficult. In this paper it is outlined how copolymers in which oligomeric segments of PTV, alternating with saturated spacer units, can be synthesized and cast as optical-quality films for NLO applications. The design of oligomeric PTV monomers and preliminary NLO characterization of the copolymers are also described

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Tetraethylene oxide-organosiloxane hybrid (TEOS), a flat membrane, was obtained by mixing solutions of tetraethylene oxide and methyltrichlorosilane in a Teflon vessel. In the frequency spectra of the linear conductivity of the ionically conductive membrane using TEOS as a matrix (TEOS/LiC104), relaxations associated with the electrode and interfacial polarizations were observed.

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Luminescence properties of Tb 3+- or Eu3+-polycarboxylate complexes in aqueous solution were investigated. The excitation bands near 300 nm for terbium- or europium-polyacrylate solutions were drastically enhanced by the addition of hydroxyl-radical generating reagents as well as ultrasonic irradiation. These spectral changes were attributed to the energy transfer from chromophore molecules formed by the hydroxyl radicals generated in both systems

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The linear polymers obtained by reacting 2,6-diaminotoluene with benzaldehyde or formaldehyde were condensed in polyphosphoric acid or aqueous HCI. The ladder polymers obtained were characterized by 1H n.m.r., FTi.r., u.v.-vis, and g.p.c.

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Bis(p-allyloxyphenyl)polydimethylsiloxanes were synthesized by equilibrium polymerization of octamethylcyclotetrasiloxane (D4) with 1,3-bis(p-allyloxyphenyl)-l,l,3,3-tetramethyldisiloxane in the presence of a base catalyst (Bu4NOH). Cleavage of allyl groups from these polysiloxanes was performed by the use of palladium (II) catalyst and diethylamine, forming ~,~o-bis(p-hydroxyphenyi)polydimethylsiloxanes in good yields.

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A detailed morphological investigation of methacrylic based block ionomers was conducted. In the case of the triblock systems, the end blocks were based on t-butyl methacrylate while the elastomeric centre block was either n-hexyl methacrylate or 2-ethylhexyl methacrylate. Upon hydrolysis of the end block the acid form of the block polymer was obtained. Neutralization of this component led to the ionic block polymer. The effect of ionic block length and the consideration of either di- or triblock architecture was studied. Though the diblock materials exhibited poor tensile properties relative to the triblock systems, the morphological features of the diblock materials were very interesting when in ionic form. Multiple scattering peaks were observed in the diblock ionomers using SAXS and this was attributed to the well ordered regions that were also observed utilizing TEM measurements. In general, good correspondence between the TEM and SAXS results was obtained. Surprisingly, long range order was less pronounced in the triblock ionomer with similar ion content when compared with its diblock analogue. Finally, the interdomain distance between the ionic domains was found to be highly dependent on ionic block length.

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Amino groups have been introduced into the phenylene rings comprising poly (phenylene ether sulphone) (PES) chains by performing nitration/reduction procedures on preformed PES and by using an aminated dichloride as a comonomer to achieve direct synthesis of aminated PES by polycondensation. It appears that side reactions can occur which cause problems with nitration/reduction procedures. The use of 2-amino-4-chlorophenyl sulphone as comonomer provides an effective means of introducing amino groups, but the copolymers obtained had inherent viscosities lower than that of homopolymer made by a comparable polycondensation procedure.

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The morphology gradient through the thickness of an injection-moulded blend of 10% by weight acrylonitrile-butadiene-styrene (ABS) and 90% by weight polycarbonate (PC) has been characterized. Brittle fracture surfaces were etched and examined both parallel and perpendicular to the injection direction in the scanning electron microscope. In the centre of the plaque, the morphology was isotropic with the ABS phase dispersed in the PC matrix as large composite rubber particles about 1 pm in diameter and smaller particles of free styrene-acrylonitrile (SAN) about 0.3 #m in diameter. About half the distance from the centre to the edge, the morphology of the free SAN phase changed from predominantly spherical to predominantly string-like. The SAN strings connected the rubber particles to form an oriented ABS bead-and-string structure that was essentially continuous in the injection direction. It was thought that the free SAN was highly extended under elongational or shear flow while remaining attached to the rubber particles because of miscibility with grafted SAN. The bead-and-string structure was retained near the edge where the melt solidified most rapidly. In the centre of the plaque, the low shear rate during mould filling and longer cooling time after mould filling favoured relaxation of the bead-and-string structure. The morphology gradient through the thickness was created by the competition between the relaxation rate and the cooling rate after mould filling. In this case, relaxation was thought to occur by interfacial-tension-driven break-up and end-pinching mechanisms to produce the dispersion of rubber and free SAN particles. Evidence to support the break-up mechanism was obtained when annealing above the glass transition temperature of PC for a matter of seconds, the timescale of mould cooling, caused the bead-and-string structure to convert to a dispersion of composite rubber particles and SAN particles.

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The optical rotation of anisotropic macromolecules depends on the direction of propagation of linearly polarized light through the molecule. The molecular optical activity is thus a tensor property, the components of which characterize the molecular structure. A study is reported in which these components have been measured for three polypeptides in helix-promoting solvents. These were poly(),-benzyl-Lglutamate), poly(7-benzyl-D-glutamate) and poly(fl-benzyl-L-aspartate). The measurement technique involved imposing orientational alignment upon the molecules. This alignment was achieved using pulsed electric fields and the optical rotation recorded over a range of visible light wavelengths. From the rates of response to the field changes, helical lengths were obtained. The implications for molecular conformations are discussed.

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