1992 рік

Novel regular network wholly aromatic polyester and polyamide films were prepared from trimesic acid (Y) and aromatic diols and aromatic diamines. Prepolymers prepared by melt polycondensation were cast from dimethylformamide solution and post-polymerized at various elevated temperatures and times to form networks. The resultant films were insoluble in any organic solvents. Heat distortion temperature Th of both polyester and polyamide films increased with increasing post-polymerization temperature and time. Polyester films of OY, prepared from Y and 4,4'-dihydroxybiphenyl ether (O) post-polymerized at 290°C for 18 h, and of BY, prepared from Y and 4,4'-dihydroxybiphenyl (B) post-polymerized at 340°C for 2 h, showed the highest Th (430°C) of the polyester films studied. Polyamide films of O'Y, prepared from Y and 4,4'-diaminobiphenyl ether (O') post-polymerized at 350°C for 2 h, had the highest Th (444°C) of the polyamide films studied. The degree of reaction, a measure of network formation, increased with increasing post-polymerization time. X-ray diffraction patterns of these network polymer films exhibited broad but distinct diffraction peaks, suggesting the formation of some ordered structure owing to the regular network formed by symmetrical trimesic acid moiety. The density of polyester films decreased and that of polyamide films increased with increasing post-polymerization time. These network polymers had tensile strengths and Young's moduli lower than the network polyester film of 2GY prepared from Y and ethylene glycol (2G). Temperature profiles of both thermomechanical analysis and thermogravimetry of polyamide films exhibited higher thermal resistance than polyester films, suggesting the formation of a carbonized structure at higher temperature.

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The dipole moments of a series of poly(thiocarbonate)s derived from bisphenol A have been determined in 1,4-dioxane and benzene solutions at 298 K. The effect of the side chain structure of the polymer and the solvent on the dipole moment are analysed. A very small influence of the polymer structure on the dipole moment is observed.

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Changes in the porous structure of the strongly crosslinked macroporous copolymers glycidyl methacrylate-ethylene dimethacrylate and styrene-divinylbenzene were studied. Via interaction with organic solvents (dioxane, methanol) changes are brought about in the specific surface areas and pore volumes, which are interpreted in terms of changes in the microporous and macroporous domains of the porous structure of the polymers. According to mercury porosimetry, there are also changes in pore distribution. The phenomenon has also been observed in microphotographs of polymer sections obtained by electron microscopy and in the sorption of solutes.

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Imide-aryl ether oxadiazole copolymers were prepared and their morphology and mechanical properties investigated. A general method for the preparation of aryl ether oxadiazole-containing d/amines has been developed in which the generation of the aryl ether linkage was the monomer-forming reaction. The electron-deficient oxazole ring activated a fluoro-substituent towards nucleophilic aromatic substitution. Facile displacement occurred at the para position of a 2-phenyl substituted oxadiazole heterocyclic since the oxadiazole can stabilize the negative charge developed in the transition state through a Meisenheimer complex, analogous to conventional activating groups (i.e. sulphone, ketone, etc.). The synthesis involved the reaction of 2,5-bis(4-fluorophenyl)-l,3,4-oxadiazole with either 3- or 4-aminophenol in an N-methyl-2-pyrrolidone/N-cyclohexyl-2-pyrrolidone solvent mixture in the presence of potassium carbonate. These novel d/amines were purified by recrystallization, polymerized with various compositions of 4,4'-oxydianiline (ODA) and pyromellitic d/anhydride (PMDA) and thermally cured, producing two series of novel imide-aryl ether oxadiazole random copolymers. The resulting copolymers showed mechanical properties comparable to PMDA/ODA polyimide with elongations in the 40% range and moduli in the 2500 MPa range. The copolymers showed Tgs in excess of 300°C. However, the thermal stability was somewhat compromised by the incorporation of the oxadiazole-containing d/amine relative to PMDA/ODA polyimide.

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Three-dimensional finite element (3-D FEM) analysis has been performed on single-edge cracked low density polyethylene to investigate the fracture mechanics for the stationary and growing crack. Input of the mechanical behaviour to the FEM calculation is derived from the uncracked specimen. It is found that, without referring to either the plastic flow theory or to the plastic deformation theory, the 3-D FEM analysis predicts the load-displacement curve of the cracked samples, the crack extension to the applied stress curve and the development of the plastic zone to acceptable agreement with the experimental results. Both the stress and strain at the crack tip are three-dimensional while those remote from the crack tip are close to the two-dimensionsl state.

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Hydrogen-bonded polymer complexes formed from poly(4-hydroxystyrene) and poly(N,N-dimethylacrylamide) were studied by cross-polarization/magic angle spinning laC nuclear magnetic resonance spectroscopy. Evidence for specific interaction was provided by a shift of ~ 3 ppm in the phenolic carbon resonance peak. The proton spin-lattice relaxation times are shorter than the values predicted by a linear model. On the other hand, the rotating frame spin lattice relaxation times, Tip, of the complexes agree with the predictions. The scale of homogeneity is estimated from the Tip data to be ~2.5 nm.

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The interference of allylic hydroperoxides in the reaction of 2,4-dinitrophenylhydrazine (DNPH) with oxidized polyisoprene was investigated. During the DNPH analysis, hydroperoxides were susceptible to acid-catalysed Hock cleavage, producing carbonyl compounds which subsequently reacted with DNPH to form additional hydrazone derivatives. Prior reduction of the hydroperoxides with triphenylphosphine (PPh3) appeared to be a satisfactory method of eliminating this problem, giving more accurate carbonyl levels.

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Interdiffusion at interfaces between deuterated polyamic acid (d-PAA) and polyimide (PI) films was investigated with forward recoil spectrometry, an ion beam analysis technique. The PI films were prepared by spin coating a solution of PAA on a silicon substrate, followed by an anneal at a temperature Ti, which produced partial or complete conversion of the PAA to PI. An overlayer of d-PAA was added, in one set of samples by spin coating from solution, and in another set by transferring (in the absence of solvents) a dry d-PAA film onto the PI surface. The bilayer samples were then either annealed at a temperature Ta or allowed to stand at room temperature. No interdiffusion occurred in the solventless transfer samples for any combination of temperatures T~ or Td from room temperature up to 400°C. Bilayers prepared by spin coating d-PAA from solution directly on partially cured PI films did, however, show significant interdiffusion distances w, which decreased with increasing values of Ti to immeasurable levels by T~ = 200°C. The decrease in w with increasing T~ is thought to be caused by a positive Flory parameter between PAA and PI which increases with the imide fraction in the PI film ; the result is an increasing immiscibility between the swollen polymer layers. Subsequent annealing of these spin-coated bilayers at a temperature T a up to 400°C was ineffective in producing any additional interdiffusion. The absence of any thermally activated interdiffusion (even for initially unimidized samples), with either the solventless-transfer or spin-coated preparation methods m

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Inverse gas chromatography (i.g.c.) has been used to calculate thermodynamic interaction parameters of polystyrene (PS) and polybutadiene (PBD) with 15 different probes of varying polarities at 155, 165, 175 and 185°C. Polymer-polymer interaction parameters were also evaluated at five different compositions of PS-PBD blends and were found to show marked probe dependence. Using various approaches such as those given by Horta et al., by Sanchez and by Chee, the experimental data have been analysed to provide probe-independent interaction parameters. It is shown that rearrangement of an equation due to Su and Patterson explains the AZ effect and gives probe-independent interaction parameters by a more simplified method.

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The effect of introducing lateral substituents in liquid crystalline poly[(trimethylene)terephthaloyl-bis-4- oxybenzoate] has been analysed. The 2,2-dimethyl derivative has been synthesized and has shown liquid crystalline behaviour. The temperature for the crystal-liquid crystal transition and the mesophase-isotropic transition have been considerably lowered with respect to the unsubstituted polymer. Such transitions have been characterized by X-ray, differential scanning calorimetry and optical microscopy and analysed as a function of the thermal treatment.

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