1993 рік

A new aliphatic block/segmented poly(amide-ester) has been prepared from lactones, diamines and dicarboxylic acids through oligomerization. In in vitro studies the polymer degrades depending on the size and nature of the blocks. In vivo studies indicate that the polymer is biocompatible and degrades to some extent. Mechanical properties, namely tensile strength and elongation at break, and X-ray crystallinity are observed to vary during the study.

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Poly(styrene-block-methyl methacrylate)s were analysed by liquid chromatography at the critical point of adsorption. Operating at chromatographic conditions, corresponding to the critical mode of polystyrene and a size exclusion mode for poly(methyl methacrylate), the molar mass and the polydispersity of the poly(methyl methacrylate) block in the block copolymers was determined. The chemical composition of the block copolymers was obtained using size exclusion chromatography with coupled density-refractive index detection, and compared to data calculated from critical chromatography experiments. The agreement of the data obtained by the different methods was found to be very good.

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Dynamic mechanical analysis (DMA), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) have been used to characterize the physical properties and morphology of a series of poly(imide-siloxane) copolymers. These copolymers based on DAPI-6F contain either a short bis(aminopropyl) terminated siloxane monomer or oligomer. The results show that the copolymers containing the oligomeric segments are phase separated. The SAXS results indicate that the domain size of the poly(dimethylsiloxane) segment is independent of the siloxane-to-imide ratio. However, the DMA results show that the high temperature maximum in E", herein defined as Tg of the imide phase, decreases with an increasing amount of the oligomeric siloxane. It is suggested that the depression of T 8 may be the result of lowering of the molecular weight of the imide segments.

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2,6-Diaminoanthroquinone (DAAQ) has been used as a non-covalently bound template in order to generate shape-selective cavities in crosslinked porous polymers based on ethylene glycol dimethacrylate (EGDMA) and divinylbenzene (DVB). Dimethylsulphoxide was used as a solvent and porogen. When acrylic and methacrylic acid were employed to form a complementary binding site within the cavity, there was no evidence for selective resorption of DAAQ and hence no evidence for shape-selective cavity formation. However, when a monomer containing sulphonic acid groups was used in place of the polymerizable carboxylic acids, stronger interaction with DAAQ was achieved and shape-selective cavities within polymers were formed as indicated by the selective resorption of DAAQ by such polymers relative to analogous non-templated polymers. Similarly selective sorption of non-functional anthracene, with a similar framework to DAAQ, was also demonstrated, confirming the shape-selective nature of the cavities

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A micromechanically based composite model which we have recently proposed is employed to study large plastic deformation and texture evolution in initially isotropic high density polyethylene (HDPE) under different modes of straining. Attention is focused on the macroscopic stress-strain response and the evolution of crystallographic, morphological and macromolecular textures in HDPE subject to uniaxial tension and compression, simple shear and plane strain compression. Comparison of the predicted results with experimental observations (e.g. stress-strain measurements, wide-angle X-ray scattering and small-angle X-ray scattering studies of deformed material) shows excellent agreement in nearly all respects.

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A new polyester, poly(2-ethyl-2-methylpropylene terephthalate) (PEMPT), as well as poly(1,5-pentylene terephthalate), poly(1,7-heptylene terephthalate) and poly(1,9-nonylene terephthalate), have been synthesized and characterized with respect to specific criteria including phase behaviour studies with bisphenol-Apolycarbonate (PC). Binary blends of the four polyesters with PC (50/50 wt%) all exhibit two amorphous phases when an inhibitor is present to prevent transreactions. When prepared without inhibitor, the same blends are single phase, indicating that transreaction has occurred between blend components. Additionally, thermal analysis shows that PEMPT is amorphous and has improved thermal stability compared to the other aliphatic-aromatic polyesters studied. These characteristics are attributed to ethyl-methyl substitution of the propylene group in PEMPT.

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Optical absorption has been used to study polyaniline at various levels of oxidation and protonation. The conversion of leucoemeraldine base to its salt accounts for the blue shift of the n-n* absorption from 3.94 to 4.17 eV. The emeraldine base has an absorption peak at 2.1 eV due to the localized benzenoid HOMO (highest occupied molecular orbital) to quinoid LUMO (lowest unoccupied molecular orbital) excitation. Protonation of the emeraldine base causes a lattice distortion of polyaniline to form a polaronic lattice structure, which accounts for the shift of the 2.1 eV absorption to 1.5 eV. Further protonation of emeraldine salt causes the breakdown of the polaronic lattice to a confined bipolaron lattice. When the acid strength of the solution is very high (96% H2SO4), most of the amine nitrogens are protonated. Characteristic absorptions of isolated quinoid imine units ( ~ 2.5 eV) and benzene units ( ~ 4.8 eV) have been found. The evolution of band structure corresponding to the optical-absorption change during the protonation of polyaniline at each specific oxidation state is studied by gradually changing the acid strength of the solution to which the polymer is subjected. We have also studied the optical-absorption change at one fixed acid strength by slowly oxidizing leucoemeraldine to emeraldine then to pernigraniline by electrochemical and chemical means. Detailed information has been obtained on the band structure changes in relation to lattice structure interconversions during the transitions between various oxidation and protonation states.

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The technique of inverse gas chromatography (i.g.c.) has been used to investigate the transitions between liquid-crystalline phase in a polysiloxane bearing cyanobiphenyl mesogens and in a low-molar-mass analogue. The transition temperatures were found by considering the variation of retention volume with temperature and also the activity coefficients of the probes used, the latter giving clearer results. The possibility of using the method to study the thermodynamics of the transitions is also discussed. Although not the most convenient method for measuring solely the phase transitions, it allows the simultaneous determination of a number of other properties, so that our results extend the already wide range of applicability of i.g.c, in polymer science.

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The time-resolved photophysical behaviour of a,a-dinaphthylpropane (~c?-DNP) in iso-octane solution at temperatures greater than 30°C is in good agreement with the predictions of Birks kinetics. At temperatures below 30°C the fluorescence decay behaviour is more complex. This has serious implications for the attempted use of ~-DNP (or indeed any other bichromophoric compound) in attempts to probe macromolecular dynamics if'forced fits' to dual-exponential functions were to be employed. The complexity of the fluorescence decay behaviour of such a simple model molecule (in which the complication of'tacticity' and/or energy migration effects are obviated) has implications regarding the interpretation of the photphyiscal behaviour of macromolecules derived from vinyl aromatic monomers.

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Spontaneous and sustained reduction and accumulation of elemental gold from chloroauric acid solution by electroactive polyaniline in the leucoemeraldine and emeraldine oxidation states have been demonstrated and explained. A typical polyaniline film can accumulate more than five times its own weight of gold ([Au]/monomer mole ratio > 2) before the reduction rate is substantially retarded by the loss of active surface area due to gold coverage.

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