1994 рік

The total helix content has been estimated by circular dichroism measurements for sodium poly(Lglutamate)/ poly(L-lysine) hydrobromide (PLGNa/PLLHBr) mixed systems in aqueous alcohols. The polyion complexes were soluble in the mixed solvents, on account of the rather low total polymer concentration (6.2 ? 10 -4 (base) mol 1-1), except when a polymer mixing ratio of 1:1 equivalents was used. It has been observed that the total helix content significantly decreases with polymer mixing, when compared to that observed in single polymer systems, while by the addition of C104, or a short-chain PLGNa, both of which stabilize the helix conformation of PLL, the respective helix conformations are almost completely retained. These experimental findings, together with those concerning the dependence of the helix content on the alcohol species, are discussed, and possible structures for the polyion complexes are proposed.

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A method has been developed for the synthesis of semicrystalline poly(arylene ether ether sulfide) materials by first preparing a soluble, amorphous sulfoxide containing precursor, then rapidly reducing the sulfoxide moiety to sulfide. The sulfoxide polymers are synthesized using conventional nucleophilic aromatic substitution reactions between difluorodiphenyl sulfoxide and diphenols. Reduction of the poly(ether ether sulfoxide)s with oxalyl chloride in conjunction with an iodide salt provides quantitative conversion of sulfoxide to sulfide within seconds, and the insoluble, semicrystalline poly(arylene ether ether sulfide) precipitates in the form of fine particles. Using this soluble precursor approach for preparing semicrystalline material allows there to be good control of molecular weight and endgroup structure.

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Copolymerization of ethylene and propylene was performed using a catalyst based on TiCI4 modified with trimethylsilanol which is soluble in toluene (diluent used in the polymerization) even after cocatalyst addition. The copolymers were analysed and their structures were found to be very similar to those obtained with vanadium catalysts

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We have determined the segregation of diblock copolymers of deuterated polystyrene (dPS) and poly(2-vinylpyridine) (PVP) to a planar interface between the homopolymers using forward recoil spectrometry. The segregation isotherms, namely the interfacial excess versus its volume fraction in the homopolymer phase far from the interface, for the diblock copolymers were measured at several temperatures. Using a self-consistent mean field (SCMF) theory, one can fit the segregation data accurately if the Flory interaction parameter Z is treated as a fitting parameter. Using this scheme, the temperature-dependent Flory interaction parameter X between PS and PVP was determined to be -0.033 + 63/T(K). In contrast to this evaluation of Z which depends heavily on a model, we have shown that the isosteric heat of segregation qs=g can be directly extracted from the experimental data. We demonstrate that the enthalpic portion of the Flory interaction parameter Za can be estimated directly from qse~, without recourse to a model of the segregation layer, and the X, from this direct method is in good agreement with that determined using the SCMF theory. These two methods provide a new approach for determining X for strongly immiscible polymers.

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A model for the Gibbs energy of mixing for the systems composed of water, neutral polymer and polyelectrolyte is established by combining the theories of Flory Huggins and Manning, and by treating the free counterions as complementary species. The phase behaviour of two model systems and its dependence on the salt concentration are studied by using the model. The basic features of the phase behaviour of the systems can be captured, and the calculated results are in good agreement with the experimental data.

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LARCTM-ITPI, an isomeric variation of the better known LARCTM-TPI and based on 4,4'- isophthaloyldiphthalic anhydride and 1,3-phenylenediamine, was evaluated as a matrix for high-performance composites. Five 30% poly(amide acid) solutions in N-methyl pyrrolidone, with stoichiometric offsets of 2.0, 3.0, 4.0, 4.75 and 5.5% in favour of the diamine and end-capped with phthalic anhydride, were synthesized and their molecular weights and molecular weight distributions determined. Importantly, high concentrations of low molecular weight species were found in all the offset compositions. Solvent/volatile depletion rates were carefully determined on thermally imidized films of the five compositions and were an important part of the composite consolidation studies. All films failed a solvent resistance test which involved immersion in acetone, methyl ethyl ketone, toluene, dimethylacetamide and chloroform for 1 min followed by a fingernail crease. A minor modification of the polymer backbone improved solvent resistance measurably. Unidirectional IM7 prepreg was made from each of the five resin solutions by standard drum-winding procedures. A workable composite consolidation cycle was developed for the 3% offset solution by conducting a parametric study involving residual solvent content, melt viscosity and composite C-scan information. The basic strategy was to B-stage the prepreg to a temperature where 98% of the volatiles were depleted while, at the same time, adequate molten resin fluidity (via incomplete imidization and residual solvent content) was retained, then apply pressure and increase temperature to complete the consolidation. This moulding cycle was then applied successfully to the remaining compositions and composites fabricated. From the processing information and composite mechanical properties, including short-beam shear strength, flexural strength and flexural modulus at room temperature, 93, 150 and 177°C, the 4.75% stoichiometrically offset end-capped polymer was chosen as the optimal matrix. Composite engineering properties for this selected composition were also obtained, including longitudinal tension, transverse flexural, longitudinal compression, interlaminar shear, short-block compression, compression strength after impact and open-hole compression (OHC). Notably, 80% of the room temperature OHC strength was retained at 177°C, indicating that the LARCTM-ITPI is an excellent high-temperature matrix material for selected future aerospace applications where solvent resistance is not a key requirement.

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The effect of the molecular character and extent of crosslinking units on polymer-analogous benzil-benzilic acid rearrangement was investigated. A typical hydrophobic styrene-divinylbenzene copolymer and a hydrophilic styrene-tetraethyleneglycol diacrylate copolymer were used as the polymer supports. Supports with crosslink densities varying from 2 to 20% were functionalized. The polymer-bound aldehydes were subjected to crossed benzoin condensation in the presence of benzaldehyde. The benzoin analogues were converted to benzils and then subjected to benzil-benzilic acid rearrangement. The products were characterized by i.r. and 13C n.m.r, spectroscopy and the extent of rearrangement was determined by chemical methods.

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The phase behaviour of the binary polymer system consisting of poly(hydroxy ether of bisphenol A) (Phenoxy) and poly(styrene-co-acrylonitrile) (SAN) has been investigated by means of visual observations, light transmission measurements, differential scanning calorimetry and dynamic mechanical thermal analysis. The influence of both the blend composition and the copolymer composition of SAN on the miscibility of these binary blends was examined. All of the Phenoxy/SANx (x= 5, 10.4, 15, 16.9, 29, and 34 wt% AN) blends studied were partially miscible. The composition of the two phases and the interaction parameters were calculated from measurements based on the glass transition temperatures.

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Water-soluble cyclocopolymers of N,N-diallyl-N-alkoxybenzyl-N-methylammonium chloride (alkyl = hexyl and octyl) and N,N-diallyl-N,N-dimethylammonium chloride were prepared by free radical polymerization at 50°C in aqueous solution. The copolymer compositions were determined by 1H n.m.r, and u.v. measurements. The solution properties of the copolymers were studied as a function of the length and concentration of pendent hydrophobic groups, copolymer concentration and electrolyte or surfactant concentration, utilizing rheological and fluorescence methods. The copolymers in dilute solutions exhibit primarily intramolecular hydrophobic associations in both pure water and electrolyte solutions. The shear-thickening behaviour observed for these copolymer in dilute and semidilute solutions is interpreted in terms of intramolecular and intermolecular associations. Addition of sodium dodecyl sulfate (SDS) to the copolymer solutions results in a large increase in the viscosity at SDS concentrations below the critical micelle concentration. Fluorescence studies suggest that the viscosity enhancement is caused by interpolymer association of polymer-SDS domains

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Polymers have been recognized to exhibit selective permeation rates to gases for more than a century. The commercial reality of this characteristic, however, occurred in the late 1970s. There has been significant commercial activity in this area which has also brought about a rapid increase in the study of polymeric structural variations to optimize the combination of gas separation and permeability (permselectivity). It has been recently noted that upper bound limits exist for the separation of common gas pairs. These limitations will be discussed along with the structural features necessary to achieve the best combination of high permeability combined with high selectivity. One of the speciality polymers receiving significant attention in the past decade is poly(trimethylsilylpropyne) (PTMSP) primarily due to a permeability to common gases an order of magnitude higher than silicone rubber. Structural variations, solvent variations, non-solvent swelling effects and flux decline of PTMSP are discussed. Flux decline, which has been reported in detail in the literature, is believed to be due to two factors. Contamination can significantly decrease permeability which comprises the reason behind many literature citations. Another factor involves a slow collapse of the structure (as cast) which can depend on the casting solvent. Non-solvent swelling promotes an instantaneous increase in permeability which slowly decays back to original values. High glass transition temperature engineering polymers (e.g. polyimides, polyarylates, polycarbonates) yield permselectivity characteristics of interest for gas separation. Structural features and variations of these polymers to achieve high permeability combined with selectivity (e.g. upper bound properties) will be discussed. Surface modification techniques comprise another route to achieve high selectivity for permeable polymers. These methods (e.g. fluorination, plasma modification, u.v. exposure) offer an additional route towards meeting the requirements for separation of gases with polymeric membranes.

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