1992 рік

The viscosity of immiscible polymer blends has been studied via application of certain aspects of rheology. A symmetric mixture rule was derived, and the deviations from the 'additivity rule' have been associated, essentially, with the properties of the interphase, with its influence on the effective volumes of the two polymers constituting the blend and with the deformability of both the interphase and the disperse phase. The rule predicts a positive deviation for a mixture with a disperse-phase viscosity (r/a) greater than that (r/m) of the continuous medium, and a much higher-viscosity interphase, i.e. r/i >> r/d/> r/re" Negative deviation is to be expected when the interphase has a much lower viscosity than those of the two pure polymers (r/a, r/m>>r/i) in the blend. The viscosity and strength of the interphase depend mostly on the specific thermodynamic interactions that led to its creation.

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Using the method of attenuated total internal reflection, infra-red spectroscopy has been used to study the kinetics of formation of the interpenetrating polymer network (IPN) formed between polyurethane and polyesteracrylate. It was found that the curing rates of the different networks are related and an increase in the polymerization rate of oligoesteracrylate leads to changes in the rate of polyurethane formation in IPN. The effects observed are explained in terms of the interdependence of the processes of network formation and microphase separation. The degree of segregation of the components in the IPN depends on the rate of formation of each of the networks.

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The process of stereocomplexation in the bulk between isotactic poly(methy1 methacrylate) and a polybutadiene-syndiotactic poly(methy1 methacrylate) diblock copolymer was studied by differential scanning calorimetry as a function of composition of the blends, annealing time and temperature. The amount of complex formed is dependent on these three parameters, while the temperature of decomposition of the complex is only dependent on the temperature of annealing. One endotherm of decomposition was observed, in contrast to poly(methy1 methacrylate) homopolymer blends, for which two endotherms referred to as T,,,, and Tm3 were generally reported. On the basis of a model proposed by Challa et al., the endotherm can be identified with T,,,,. The absence of the second endotherm can be explained by the presence of the ‘foreign’ elastomer sequence preventing the formation of the lamellar crystals attributed to Tm3 in the model. For annealing temperatures larger than 14O”C, no complex is formed.

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The properties of an epoxy composite filled with china clay, CaF 2 and glass beads were investigated. It was found that a boundary layer formed when fillers were added to the epoxy matrix. The properties of the boundary layer are different from those of the matrix. The density, modulus and tensile strength of the boundary layer were obtained and the influence of the boundary layer on the properties of composites was discussed.

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Heat capacities were measured for three aromatic polysulphones : poly (1,4-phenylene sulphonyl), PAS; poly(oxy-l,4-phenylene-sulphonyl-l,4-phenylene), PPES; and poly[oxy-l,4-phenylene-sulphonyl-l,4- phenylene-oxy-l,4-phenylene-(1-methylidene)-l,4-phenylene], PBISP; from 150 to 620K using differential scanning calorimetry. These new data, along with the prior ATHAS (Laboratory for Advanced Thermal Analysis, University of Tennessee) recommended experimental heat capacities for three aliphatic polysulphones : poly ( 1-propene sulphone ), P 1PS ( 20- 300 K ) ; poly ( 1 -butene sulphone ), P1BS (100-300 K); poly(1-hexene sulphone), P1HS (20-300K), were fitted to an approximate frequency spectrum below their respective glass transition temperatures. The ATHAS computation scheme was used to compute the heat capacities that arise from these vibrations from 0.1 to 1000 K. The 01-temperature changed from 685 K for PIPS to 587 K for P1HS while for PPES and PBISP much higher values (799.5 K and 777.8 K) than the other phenylene polymers analysed at ATHAS, were obtained. Using these data and the smoothed experimental liquid heat capacities, the glass transition temperatures for PAS, PPES and PBISP were obtained at 492.6,497.4 and 458.2 K. The corresponding values for ACp were 18.1, 37.7 and 126.6 J K-t tool-1, respectively.

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Rigid rod-like liquid-crystalline polymers are currently in high demand because of their high modulus and rigidity, and good orientation properties. Gelation is an important phenomenon encountered in lyotropic solutions of polymeric liquid crystals, and this is manifested in fibre spinning and many biological systems. We will focus our attention on the behaviour of gels formed by the synthetic polypeptide, poly (~,-benzyl ~,l-glutamate) (PBLG), in benzyl alcohol (BA). More basic than determining the phase boundaries are the questions concerning the definition and identification of the gel phase and the molecular origins of such a phase, along with the added complexity of the dynamics in each phase. In this work, we attempt to make a systematic study of each phase for the PBLG-BA system, using rheological, thermal and light scattering experiments.

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Stat-copoly(oxyethylene-oxypropylene)~ were prepared by anionic polymerization initiated by potassium methoxypropanol in the presence of 18-crown-6 ether, and were characterized by g.p.c. and n.m.r. Molecular weight distributions were narrow. Reactivity ratios, determined from composition and from sequence distribution, were rE = 3.1-3.3 and rp = 0.31-0.33, in good agreement with reactivity ratios determined for polymerization without added crown ether. Diblock copolymers with one stat-copoly(oxyethyleneoxypropylene) block and one poly(oxyethylene) block were prepared by sequential polymerization, and were characterized by g.p.c. and n.m.r.

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Poly(vinyloxyacetic acid) and its metal salts show polyelectrolyte behaviour in water. The order of counterion binding to this polymer is K + > Na + > Li + > Ca 2+. The glass transition temperature (Tg) of poly (vinyloxyacetic acid ) with low ionic content and that of its metal salts are the same as that of poly (vinyl alcohol) whereas poly(vinyloxyacetic acid) with high ionic content shows an increased Tg.

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Copolymers of acrylonitrile with a furfuryl alcohol resin have been prepared by a free radical reaction, and have been characterized by n.m.r, and i.r. spectroscopy. Their t.g.a, has been performed in air and in a nitrogen atmosphere, to permit the recognition of a number of stages in the weight loss process. D.s.c., also in air and in nitrogen, has identified a number of exothermic and one endothermic process in the copolymers. Solid state cross-polarization/magic angle spinning laC n.m.r, spectroscopy and i.r. spectroscopy has been used to obtain some insight into the chemistry of the various chemical changes, which in air are completed by combustion and in nitrogen leave a carbon.

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It is commonly stated that polyacrylonitrile (PAN) and polymethacrylonitrile (PMAN) undergo a cyclization reaction, which may be thermally induced or caused by addition of base to a polymer solution. However, in our previous work with PAN, no evidence for cyclization was found; instead, it was shown that base could abstract the methine proton leading to azomethine crosslinking and gelation. PMAN has no methine proton and hence this crosslinking mechanism should not operate. However, when strong base was added to a PMAN solution, gelation still occurred. It is proposed that base also induces intermolecular nitrile crosslinking reactions. No evidence for cyclization was found in base-treated or thermally treated PMAN. The results of dynamic mechanical testing of thermally discoloured PMAN films were also more consistent with a slight degree of crosslinking rather than extensive cyclization.

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