1993 рік

The C=O stretching frequencies of alkyl esters and polyesters are used as a probe to study the possible existence and the extent of dipole~tipole interactions between ester groups in these systems. The dynamics of a linear array of electric dipoles is worked out. The results account for the observed infra-red and Raman spectra of solid methyl acetate and ethyl acetate, but fail to account for the multiplet structure observed for one of the polyesters, which shows liquid-crystalline properties. Calculations show that the vibrational spectra are a good probe only of intermolecular interactions at short range.

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ct,co-Diaminopropyl terminated polycyanopropyl methylsiloxane-polyurea is studied by high resolution 1H n.m.r. In concentrated dimethylformamide (DMF) solution, there are no hydrogen bonds between polyurea and DMF, and between polyurea and water. Hence, solvent effects can be ignored. There are several NH reasonances in the IH n.m.r, spectra. The different chemical shifts are due to different types of hydrogen bonds. At higher temperatures, hydrogen bonding of the NH groups is not dissociated, and the relative amounts of each NH peak remain the same in the temperature range 23-82°C. The chemical shift changes of the NH group forming hydrogen bonds are greater than those of free NH with increasing temperature. The morphology of the polyurea chain in concentrated DMF solution appears to be similar to that in the solid state from the two-dimensional NOESY spectrum.

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Poly(poly(ethylene glycol)maleate) (PPEGMA) was synthesized from poly(ethylene glycol) of molecular weight 200 with maleic anhydride in a molar ratio of 1:I. PPEGMA was then blended with diglycidyl ether of bisphenol A (DGEBA) in various ratios. The formation of hydrogen bonds between PPEGMA and DGEBA was investigated with FTi.r. These blends were then cured with benzoyl peroxide and m-xylenediamine simultaneously to obtain simultaneous interpenetrating polymer networks (SINs). Cure behaviours via exothermic peaks were recorded by dynamic d.s.c. The SINs thus obtained were characterized with rheometric dynamic spectroscopy (r.d.s.) and d.s.c, to check the compatibility of the two constituent networks. Gel fractions were measured with a Soxhlet extractor using acetone as solvent. Hydrogen bonding in the PPEGMA/DGEBA blend was evidenced from the Vc~_ o shift to lower wavenumber. During SIN formation, dynamic d.s.c, showed a shift of the exothermic peak to a higher and broader temperature range, indicating a network interlocking effect which was overcome by higher temperature. Full compatibility of PPEGMA/DGEBA SINs was found for all compositions. The compatibility between PPEGMA and DGEBA was supported from the inner shifts of a single damping peak in r.d.s, and a single glass transition in d.s.c, for each of the SINs.

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Nylon 13,13 samples were prepared by various solvent-casting and thermal-treatment methods. Melt-quenched material showed broad, amorphous-like peaks in the X-ray powder pattern (at 20=21 ° , 4.2 A) and both the ~3C and 15N solid-state n.m.r, spectra. Two different crystal forms of this polymer could be generated using different methods: a type A form was obtained by extended annealing just below the melting temperature and by film casting from 1,1,1,3,3,3-hexafluoroisopropanol, while a type B form developed on precipitating from m-cresol into methanol or film casting from m-cresol. The X-ray pattern for type A was similar to those of other nylons possessing an or-crystal form, although the n.m.r, data, especially the strong, sharp 15N peak at 88.7 ppm, was more consistent with a 7-phase. The type B crystals gave an X-ray pattern similar to those of other y-form nylons and to the pseudohexagonal phase observed in some homo- and copolyamides. The n.m.r, data for the type B form (especially the sharp ~SN peak at 87.3 ppm) seemed to indicate an amide conformation of c. 30 ° with respect to the planes of the attached all-trans methylene chains; this value is half-way between those of the ct and 7-crystal forms of most nylons (~ 5N chemical shifts of c. 84 and 89 ppm, respectively). We believe these crystal forms are unique to nylon 13,13 but have insufficient data to further describe the molecular conformations and crystalline packings that correspond to each.

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By monitoring the thermal decomposition of poly(1,6-di-N-carbazolyl-2,4-hexadiyne), through the use of an electron spin resonance (e.s.r.) spectrometer, it was possible to measure the spin concentrations associated with the decomposition process. Two types of experiments were conducted: in one the decomposition reaction was carried out within the e.s.r, unit, while in the second the decomposition was performed externally under an inert atmosphere, after which the decomposed material was examined. Both types of experiment yielded similar results, and these appeared to exclude a free-radical chain mechanism as the major mechanism of decomposition. The proposed mechanism involves side-group cleavage, followed by hydrogen abstraction by the carbazole radical, to form carbazole as the main reaction product.

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The use of sequential emulsion polymerization to prepare toughening particles which comprise two, three and four radially alternating rubbery and glassy layers is described. The conditions which lead to control of particle size and morphology are discussed. The particles were crosslinked during their formation in order to ensure that they retained their size and morphology during blending with poly(methyl methacrylate) (PMMA). In this way, rubber-toughened (RT) PMMA materials with rubbery phases of predefined particle size and morphology were produced, as confirmed by transmission electron microscopy. The glass transitions of the three types of RTPMMA materials were essentially identical because the matrix PMMA was common to each blend and because the rubbery and glassy phases of each of the types of toughening particle were identical in composition

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This paper investigates the effect of n-dodecyl mercaptan (n-DDM) as a chain transfer agent on the molecular weight of poly(methyl methacrylate). The transfer constant of n-DDM was calculated at different temperatures; the activation energy and frequency factor for an Arrhenius equation of transfer constant were then obtained.

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The chemical structures of copolymers formed in the transesterification of polycarbonate/poly(ethylene terephthalate) blends during melt processing were deduced from the 1H n.m.r, spectra of reaction products which were extracted in CH2C12 solvent (extracted soluble and insoluble products). The changes in the extent of reaction with the reaction conditions (reaction time, temperature and blend composition) were also interpreted by the changes of peak intensity of typical peaks in 1H n.m.r, spectra.

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The morphological features of side-on fixed liquid crystalline polymers in an oriented state are investigated using polarizing microscopy, small angle light scattering (SALS) and infra-red dichroism techniques. A conventional side-chain polymer with mesogenic units attached longitudinally to the backbone is also studied for comparison. Banded texture usually only reported for main-chain liquid crystalline polymers is observed for these side-on fixed polymers under the crossed polarizing microscope, and SALS measurements also show typical grating diffraction patterns. This implies that side-on fixed rigid mesogens may significantly affect the conformation of the main chain of molecules, and the molecule as a whole may become rather rigid, exhibiting behaviour similar to that of the main chain. Infra-red dichroism measurements indicate that the main-chain axes of the molecules tend to orient in directions close to the shear direction. The side-on fixed mesogens are packed around the backbone, but their axes are not parallel to the latter.

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Phenolphthalein poly(ether ether sulphone) (PES-C) was found to be miscible with uncured bisphenol-A-type epoxy resin, i.e. diglycidyl ether of bisphenol A (DGEBA), as shown by the existence of a single glass transition temperature within the whole composition range. Miscibility between PES-C and DGEBA is considered to be due mainly to the entropy contribution. However, dynamic mechanical analysis (d.m.a.) and scanning electron microscopy (SEM) studies revealed that PES-C exhibits different miscibility with four cured epoxy resins (ER). The overall compatibility and the resulting morphology of the cured blends are dependent on the choice of cure agent. For the blends cured with amines (4,4'-diaminodiphenylmethane (DDM) and 4,4'-diaminodiphenylsulphone (DDS)), no phase separation occurs as indicated by either d.m.a, or SEM. However, for the blends cured with anhydrides (maleic anhydride (MA) and phthalic anhydride (PA)), both d.m.a, and SEM clearly show evidence of phase separation. SEM study shows that the two phases interact well in the MA-cured blend while the interface between the phases in the PA-cured blend is poorly bonded. The differences in the overall compatibility and the resulting morphology between the amine-cured and anhydride-cured systems have been discussed from the points of view of both thermodynamics and kinetics.

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