1999 рік

The crystallization behavior of a series of ethylene–octene copolymers synthesized using metallocene catalysts was studied using the Ding–Spruiell method of rapid cooling. In conventional crystallization experiments it was found, as expected, that the spherulite growth rates varied with octene content and molecular weight. When studied at rapid cooling rates the polymers generate their own pseudo-isothermal crystallization temperatures, in agreement with Ding–Spruiell’s studies on other systems, however, at the lowest temperatures of crystallization, the spherulite growth rates of all of the copolymers studied merge and are virtually indistinguishable. The results indicate that there is a major change of crystallization mechanism under these conditions, of considerable relevance to polymer processing operations.

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Time-resolved small-angle X-ray scattering (SAXS) measurement was carried out to trace the structural change of polyethylene (PE) during the isothermal crystallization from the melt. All kinds of PE samples of high-density PE, linear low-density PE, and deuterated highdensity PE were found to show essentially the same SAXS pattern changes, although the crystallization rates were different among them. The thus obtained SAXS data were combined with the previously reported FTIR data [Tashiro K., Sasaki S., Kobayashi M., Polym J, 1998;30:485] and could be interpreted quantitatively by dividing into the following three time regions: (1) immediately after the sample was cooled to the crystallization temperature, the density fluctuation in the molten state increased, resulting in the generation of the conformationally disordered short trans segments. (2) The disordered trans segments experienced the conformational ordering to the orthorhombic-type trans-zigzag form. These regular chain segments were aggregated to form a crystalline lamella of ca. 50 Å thickness. This separation of the system into the high (lamella) and low density (amorphous) regions occurred with ca. 800 Å period. (3) These isolated lamellae were stacked more densely by generating new lamellae in between the already existing lamellar layers, creating a structure of ca. 400 Å period.

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It was observed that some water soluble products were formed during the electrochemical synthesis of polyaniline, and Raman spectroscopy can be used to detect those products. The amount of water soluble products increases with increasing electrolysis potential and the peak observed at 1620 cm-1 is characteristic for these products. Rinsing the polyaniline coated electrode with water even once removes the soluble products from the polymer, which indicates that care must be taken in polyaniline characterization studies during washing, solvation and doping-undoping processes. The transition of H2S04-doped polyaniline to undoped form by treating with 1.0 M NaOH takes place very rapidly in high yields which can be followed by in situ Raman spectroscopy

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The quaternary ammonium salt, N,N-diallyl-N-carboethoxymethyl-N-methylammonium chloride (7), has been synthesised in excellent yield. The monomer (7), on polymerisation in water solution using ammonium persulfate as an initiator, afforded the polyelectrolyte 8. The polyelectrolyte (8), on acidic hydrolysis, gave the polyampholyte 9 in excellent yield. The solution properties of these polymers are discussed in detail. The polyampholyte 9 showed 'antipolyelectrolyte’ behaviour.

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The cyclic hexamer of phenylene sulfide (CHPS) is studied as a precursor of poly(p-phenylene sulfide) (PPS). The CHPS is one of the soluble components obtained by the extraction of poly(p-phenylene sulfide) with tetrahydrofuran (THF). Differential thermal analysis (DTA) is used to verify the purified cyclic compound. Fourier transform-infrared spectroscopy (FT-IR) and Raman spectroscopy are also employed. The spectra of the CHPS are compared with those of PPS and interpreted based on the symmetry of the molecules. Specifically, the C–H outof-plane bending modes (840–800 cm ⫺1) are indicative of the crystal structure and are utilized to identify two crystalline forms, a and b, of the CHPS. The spectrum of the polymer obtained from the CHPS is also reported.

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A series of random copolyesters with reasonably high molecular weights were synthesized with varying composition by the bulk copolycondensation of ethylene glycol with dimethyl isophthalate (DMI) and dimethyl terephthalate. Compositions and molecular weights of the copolyesters were determined by 1H NMR spectroscopy and viscometry, respectively. The copolyesters containing DMI of >20 mol% and <90 mol% are crystallizable, whereas the copolyesters with DMI <20 mol% and >90 mol% are amorphous. For the copolyesters containing DMI of >10 mol%, crystallization behaviors were non-isothermally investigated by calorimetry and analyzed by both modified Avrami and Ozawa approaches. Regardless of the composition, the value of the Avrami exponent is 2.8–3.5, depending on the cooling rate, whereas the value of the Ozawa exponent is 2.1–2.6, depending on the temperature. These results indicate that the nucleation and growth mechanisms of the copolyesters are apparently identical to those of poly(ethylene terephthalate). However, the crystallization rate is decreased by incorporating the DMI unit into the polymer backbone and also by lowering the cooling rate. In addition, the crystallization activation energy is found to be increased by incorporating the DMI unit into the polymer backbone. However, both of the analytical approaches show a big discrepancy in the estimation of the exponent which is critical to identify the type of nucleation and growth mechanism in the non-isothermal crystallization even though they have been derived from the same Avrami approach.

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The orientational behaviour of mesogenic chromophores in side-chain liquid crystalline polysiloxane subject to an external electric field was investigated by the measurement of second harmonic generation (SHG). The rise and decay rates of the electric-field-induced SHG intensity in the crystalline state were found to be slower than those in the amorphous state; furthermore, the SHG intensity in the crystalline state was found to be weaker than that in the amorphous state. Analysis of the rise and decay rates of the electric-field-induced SHG intensity suggested that the mesogenic chromophores in the amorphous state move independently with other mesogenic chromophores and with the siloxane backbone, whereas those in the crystalline state move cooperatively with them

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The photo-induced copolymerization of electron donor/electron acceptor monomers has been studied by real-time infrared spectroscopy. With maleimide/vinyl ether mixtures, the reaction was found to proceed rapidly upon u.v. exposure in the absence of oxygen to reach nearly 100% conversion within seconds. The two monomers disappeared at similar rates, with formation of an alternating copolymer. Similar results were obtained with maleimide/N-vinylpyrrolidone and maleimide/styryloxy combinations. Highly crosslinked polymer networks have been produced by photo-induced copolymerization of bis-maleimide and divinyl ether monomers. These photoinitiator-free formulations were found to be less sensitive to oxygen inhibition than typical u.v.-curable acrylate resins. N-substituted maleimides were also shown to act as monomeric photoinitiators by inducing the polymerization of acrylate monomers upon u.v. irradiation.

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A series of six mesogenic dimers were prepared containing terminal 4’-methoxyphenyl-4-octenyloxybenzoate groups, of the general formula [MeOC6H4O(O)CC6H4O(CH2)8SiMe2]2R, where R ˆ –CH2 –, –(CH2)2 –, –(CH2)3 –, –SiMe2 –, –O– and –NH–. Their liquid crystal properties were compared with those of the structurally relevant side chain polymers with the same mesogenic moiety: polycarbosilanes, polyethylene, and polysiloxane. It is shown that the low molecular dimers can be used as models for evaluating and predicting mesogenic characteristics of macromolecular systems with backbones structurally equivalent to spacers of the dimers.

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Influences of casting solvent on the microphase-separated structures of poly(2-vinylpyridine)-block-polyisoprene films were studied by transmission electron microscopy and small-angle X-ray scattering. The variations of the structures obtained were consequences of vitrification of microdomain structures developed during the solvent casting processes. The various microphase-separated structures were properly understood by considering the Hansen’s solubility parameters of the solvent and the copolymer, which quantify the polymer–solvent interactions in the system.

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