1994 рік

This paper describes the application of molecular mechanics modelling to study the solid-state structure of the thermotropic copolyester prepared from p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid. X-ray analysis of as-spun fibres shows that the structure consists of _parallel, hig_hl.y extended chains of completely random comonomer sequence which are packed on an orthorhombic pseudo-hexagonal network and ordered in three dimensions. Molecular models for arrays of chains of the 75/25 copolymer were constructed with chain extension and lateral packing as suggested by the X-ray data. Typical starting models consisted of 19 non-identical sequences of 12 monomers in a variety of conformations. The models were optimized by potential energy minimization using the SYBYL '-~ software package. Results for minimization of 20 such arrays, with different sequences and starting conformations, suggest that there are a large number of multiple minima of approximately equal energy. The main effect of the refinement was to change the aromatic ester torsion angles and thus eliminate the bad contacts between adjacent chains. In the final models, the aromatic ester torsion angles are distributed about means that are close to those observed in low molecular weight model compounds. Most importantly, the potential energies of the copolymer arrays are similar to those predicted for analogous models of the two homopolymers, indicating that there are no significant problems in packing non-identical chains of the copolymers on the same lattice. In addition, we have simulated the X-ray diffraction data by calculating the cylindrically averaged scattering intensity transforms for the models of arrays of chains. We find that even the small arrays considered here predict the observed Bragg reflections on the equator and first layer line, as well as the non-periodic meridional maxima, and the results are sensitive enough to allow for selection between different possible conformations.

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New aromatic polyesters with rigid quinoline units in the chain have been synthesized in order to investigate the possibility of generating materials that exhibit liquid crystalline behaviour in the melt. Similar materials containing 2,6-naphthalene units in the chain have also been prepared and compared with the quinoline polymers.

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Polymers subjected to ion beam or ? irradiation undergo structural modifications, which lead to an increase in refractive index for some materials, such as poly(diethylene glycol bis(allyl carbonate)) (CR39) and polycarbonate. The refractive index variation achieved with ion beam irradiation is sufficient to produce optical waveguides in CR39. The waveguide losses have been systematically studied in order to apply this technique to integrated optics (microstructure fabrication). A fundamental study using various spectroscopic methods (i.r. and u.v.-visible) has also been carried out, with the aim of gaining a better understanding of the structural modifications of polymeric materials caused by irradiation

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A study of the development of molecular orientation and crystalline structure during the transverse drawing of one-way drawn poly(ethylene terephthalate) films has been carried out. The influence of the size of the crystallites in the one-way drawn film and the influence of the transverse drawing temperature have been studied. It is shown that the deformation mechanisms appear to depend on the size of the crystals initially present. Films containing small crystals lead to a higher orientation and larger crystalline structures oriented along the transverse direction. The influence of the second drawing temperature can be understood as a result of the importance of molecular relaxation and crystallization, both of which are enhanced by elevated temperatures.

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Different macroscopic structures in poly(7-benzyl-L-glutamate)(PBLG) films were prepared by spin coating using different preparation methods. These structures were analysed between two polarizers or using polarization microscopy. The main parameters for creating structures during the spin coating process have been determined. In particular, the influence of coriolis forces during the spin coating process and solution properties were studied and resulted in a proposal for the mechanism of the production of structures

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Electrochemical oxidation of indole, CsNHT, in a non-aqueous medium, such as a solution of LiC104 or LiBF4, dissolved in acetonitrile, leads to the formation of polyindole, an air stable conducting polymer that exhibits electrochromic properties. The room temperature electrical conductivity, in the range 5 x 10-3-8 x 10-2S cm-1, depends slightly on the nature of the counterion

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Blends of a linear and a lightly branched polyethylene were prepared by solution blending and in the melt, by mixing in a screw extruder, and the phase morphologies were compared. First, the melt phase behaviour of the solution-blended system was studied by differential scanning calorimetry and transmission electron microscopy. A loop of liquid-liquid phase separation was found at low linear-polyethylene content. Three melt-mixed blends were then prepared and characterized, again by differential scanning calorimetry and transmission electron microscopy. The general pattern of phase behaviour of these melt-mixed blends was similar to that obtained by solution blending the same pair of polymers (i.e. a region of phase separation was again found at low linear-polyethylene content). Where the phase behaviour allowed mixing, the screw extruder produced blends with uniform composition throughout the sample. The morphologies of the melt-mixed materials showed enhanced nucleation, compared with the solution-blended materials, and orientation effects, particularly at low linear-polyethylene content

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The impression creep behaviour of acrylonitrile-butadiene-styrene (ABS) polymers with various butadiene contents was investigated under punching stresses of 10-120 MPa and at temperatures from 330 to 390 K (T~ = 376 K). It was found that the creep resistance of the ABS polymers decreased with increasing butadiene content. The impression velocities in the steady-state region were analysed using a theory involving thermally activated processes. The temperature within the testing range had little effect on the activation shear strain volume, which increased with increasing butadiene content. The slope between the activation enthalpy and temperature increased gradually when the temperatures were below 353 K and then became steeper when the temperature approached the glass transition temperature. The activation enthalpy reached a maximum of 1050 kJ mol - 1 at 380 K and then decreased upon further increase in temperatute. Two parallel deformation mechanisms were proposed to explain this behaviour. One is a stress activation slip process which dominates at temperatures below the glass transition temperature, and the other is a free volume assisted shear process which dominates at temperatures higher than the glass transition temperature

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The morphology of solution-cast thin films of wholly aromatic thermoplastic polyimides (TPIs) with various molecular weights (M,= 3490-85 800) was studied using transmission electron microscopy iTEM). Thin TPI films suitable for TEM studies were prepared from 0.3% solution in p-chlorophenol/phenol cast onto hot polyphosphoric acid, where the solvent was evaporated. A TPI oligomer of M,=3490-6500 forms droplet-like structure (D structure) during casting, whereas TPIs with higher molecular weights (M,,.= 23 900-85 800) form ellipsoidal and elongated structures. On heating the as-cast film of TPI with M,,.=3490, the D structure is converted into a flat, layer structure with extended chains, which gives an electron diffraction pattern of the single-crystal type. On the other hand, long curved crystals with folded chains develop in the D structure of a TPI with molecular weight of 6500. The supermolecular structures of TPIs with higher molecular weights (M,=23 900-85 800) are noticeably affected by the molecular orientation in the original structure of the as-cast films. Oriented crystallization occurs in the elongated structure, while lamellar crystals develop in the D structure or ellipsoidal structures.

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Sulfonation of nylon-6 has been widely studied via solution phase reaction processes, which involve dissolution of the base polymer in a strong solvent. In this paper, novel solid phase reaction technology was adopted to induce the addition of the sulfonate side chain onto the backbone of nylon-6 using 1,3-propane sultone. The reaction of the polymer with the reagent, which was catalysed by dimsyl anions, was carried out at 65°C in a specially designed, well-mixed reactor. The reaction materials remained as free-flowing powders through the process. A sulfonate level of 1.32 mol% was achieved. The conversion of the 1,3-propane sultone was 23.3%. The sulfonation was qualitatively identified with FTi.r. and d.s.c. Its sulfonate level was determined by quantitative measurement of sulfur and nitrogen content of the treated polymer.

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