1993 рік

Block copolymers with poly(tetramethylene glycol) (PTMG) spacers of different length and the 4,4'-(terephthaloyldioxy) dibenzoyl unit have been synthesized by high temperature solution polycondensation. The influence of the spacer length on thermal behaviour and solid phase structure of alternating polyesters in comparison with pure PTMG has been determined by d.s.c, and WAXS investigations. Up to spacer molecular weights of 650 g mol- 1 (degree of polymerization, DP ~ 9), polymers with thermotropic liquid crystalline phase behaviour are obtained. Above spacer molecular weights of 1000 g mo1-1 (DP~ 14), the coexistence of two crystalline phases resulting in polymers with block-like character is discussed.

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A previously published solution to the Seto-Frank equations (Mansfield, M. L. Polymer 1988, 29, 1755) that predicts an elliptical profile for the growing crystal can be derived using straightforward geometrical arguments and the known properties of trivial solutions. This simplified derivation clarifies several misconceptions generated by the original derivation.

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The copolymerization of 3-(S)-[(benzyloxycarbonyl)methyl]-l,4-dioxane-2,5-dione (BMD) and L-lactide (LAC) was carried out in bulk at relatively low BMD/LAC feed ratios with stannous 2-ethylhexanoate as the catalyst. The resulting copolymers were subjected to hydrogenolysis at atmospheric pressure in the presence of a palladium on charcoal catalyst to remove the pendant benzyl groups quantitatively. The deprotected copolymers consisted of L-lactic (L), glycolic (G) and L-~-malic acid (M) repeating units, with the copolymer composition being almost identical to the monomer feed composition. ~ 3C n.m.r, spectroscopy revealed that the BMD units (G-M) had been randomly incorporated into the copolymer (L-L). These poly(c~-hydroxy acid)s with pendant carboxyl groups were found to hydrolyse more rapidly than poly(L-lactide), because of the water-absorbing and catalytic activities of the carboxyl moieties. They were allowed to react with p-azidophenacyl bromide in the presence of triethylamine to form photo affinity labelling groups at the carboxyl functionalities. These findings suggested that the malic-acid-containing poly(~-hydroxy acid)s should have a high potential for use as functionalized bioresorbable polymers

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The shear and transient isothermal extensional flow properties of a semicrystalline and an amorphous thermotropic liquid crystalline polymer are investigated. Independent estimates of the relationship between extensional viscosity and strain rate are derived from the measurement of (i) pressure loss in converging flow and (ii) filament tension in isothermal fibre spinning. The former material, a copolyester of hydroxybenzoic acid and naphthoic acid, flows readily in extension and shear. Results for the amorphou

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Intrinsic viscosities [t/] of bisphenol A polycarbonate in dichloromethane, tetrahydrofuran and a mixture of 1,1,2,2-tetrachloroethane and toluene (78.5 wt% toluene), all at 25°C, have been determined for 13 fractions ranging in weight-average molecular weight M w from 2.3 ? 103 to 2 ? 105. To estimate ((S2)o/M)o~ (the ratio of the unperturbed mean-square radius of gyration to the molecular weight M at infinite M) of the polymer, the [t/] data were analysed on the basis of the theory of Yoshizaki et al. for unperturbed touched-bead, worm-like chains but, in actuality, with the Bushin-Bohdaneck:;, method applied. It is shown that the slope of a plot of (M2/[q]) 1/3 versus M 1/2 at low Mw, where excluded-volume effects on [r/] are negligible, gives ((S2)o/M)o~ directly to a good approximation. The estimated ((S2)o/MLo values for the polycarbonate in the three solvents are all (2.2_+0.2)x 10-3nm 2, and are in good agreement with the literature data from small-angle neutron scattering in the bulk state. Excluded-volume effects on [q] in the tetrachloroethane toluene mixture are significant only for Mw above 10 5, while those in dichloromethane and tetrahydrofuran are appreciable for Mw above 5 ? 10 3 to around 10 4, or above 5 10 in terms of the Kuhn segment number.

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The influence of elementary reactions (linear polymerization and crosslinking) on the development of the glass transition temperature (T~) of diglycidyl ether of bisphenol A/diaminodiphenylsulfone (DGEBA/DDS) epoxy resin system has been analysed quantitatively according to a proposed model. The model was derived on the basis of the reaction mechanisms observed in the curing system and the assumption that the Tg has individual linear relationships with the degree of conversion of the two reactions. The conversions of elementary reactions during the cure were obtained experimentally by measuring the changes in the concentrations of epoxy, primary and secondary amine groups with time by near-infra-red spectroscopy. The Tg values were measured by differential scanning calorimetry (d.s.c.). In addition, and for the purpose of comparison, the overall conversion of the system was also obtained from d.s.c, in a dynamic scanning mode. The conversion-time data from the two different techniques were consistent. The proposed model successfully predicted the separate increases in T s due to the linear polymerization and due to the crosslinking reactions. The Di Benedetto equation and the viscoelastic model of Gan et al. are also discussed

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Wide-angle X-ray diffraction techniques are employed to characterize the structure of 'as-made' and heat-treated fibres produced from nematogenic poly(m-phenylene terephthalate), where the molar fraction of the disruptor m-phenylenedioxy units is 0.25. As in the case of previously investigated poly(p-phenylene isophthalate)s, the 'as-made' fibres consist of a paracrystalline array of chains aligned along the fibre axis. Heat-treated fibre contains a mosaic of thin crystallites, consisting of m-phenylene terephthalate sequences, embedded in a paracrystalline matrix. A non-planar chain conformation, arising from the presence of m-phenylenedioxy units, is reflected in the shortening of the crystallographic repeat in the chain direction compared with that found for the poly(p-phenylene isophthalate) fibres.

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For tetrafunctional formulations, Flory’s classic analysis yields the value of 58% for conversion at gel point. This study utilizes a recently developed mechanistic kinetic model for epoxy-amine reactions to calculate the time needed to reach 58% conversion. That time was then compared to the gel time determined from rheological measurements and the two were found to be in superb agreement

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Macroporous copolymers of glycidyl methacrylate with ethylene dimethacrylate [poly(GMA-co-EDMA)] were prepared using poly(methyl methacrylate) and polystyrene of various molecular weights as a porogen, either pure or in toluene solution. The polymeric porogen remains partly incorporated in the polymer beads. The effect of the polymeric porogen on the shape and size of the particles, porous structure and particle morphology has been studied. The fraction of the oxirane groups accessible to chemical reaction with variously bulky substrates was determined in the particles. Accessibility of the oxirane groups was characterized by the e.p.r, spin-label technique. Quaternary ammonium derivatives of poly(GMA-co- EDMA) exhibited high catalytic activity in nucleophilic substitution.

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The stability of sodium-2-acrylamido-2-methylpropanesulfonate (P), copolymerized with acrylamide (M) or acrylic acid (A), towards amide hydrolysis at > 100°C is examined. Two copolymers, with average structural sequences of MMMP (polymer I) and APAP (polymer II), were aged at high temperature in 0.1 N NaC1 and the hydrolysis monitored by integration of carbonyl resonances. M hydrolysis in polymer I at pH 8 (energy of activation= 85.9 kJ mo1-1) is 10 times greater at 150°C than at 120°C and is unaffected by the presence of P. P hydrolysis occurs in two steps for both polymers at 150°C. The initial hydrolysis rate increases dramatically after half of the P units are hydrolysed. Intramolecular P hydrolysis catalysed by an adjacent dissociated carboxylate in A is proposed to explain the rapid hydrolysis. Nearby Ps prohibit this hydrolysis. The initial P hydrolysis rate in polymer II is enhanced five times on decreasing the pH from 8 to 6 due to decreased Coulombic repulsion between hydroxide and the polymer. At pH 8 and 150°C, P in polymer II is two times more stable than in polymer I lasting 9 days before complete hydrolysis occurs.

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