1994 рік

In this paper we describe the synthesis and characterization of a new series of diarylsiloxane polymers, in which the aryl substituents are either m-tolyl, 4-methoxyphenyl or 4-propylphenyl. The polymers were prepared by the ring-opening anionic polymerization of cyclic trimers in solution at high temperatures. The structure and compositions of the cyclic trimers were confirmed by ~H and 29Si n.m.r. The new diaryl polymers are all highly crystalline, and each melts to a liquid crystalline state. The crystal-liquid crystal transition temperatures depend on the nature of substituents and follow the order: di(4-methoxyphenyl) di(p-tolyl) > di(phenyl) > di(4-propylphenyl) > di(m-tolyl). The transition temperatures of polydi(4-methoxyphenyl) siloxane and polydi(p-tolyi)siloxane are both very high (300°C). The solubility of the diarylsiloxane polymers is strongly affected by the nature of the aryl substituents. Polymers having di(4-methoxyphenyl), di(p-tolyl) or di(phenyl) substituents are only soluble at temperatures above 150°C in solvents such as dimethylsulfoxide and diphenyl ether. Polydi(m-tolyl)siloxane and the mixed poly(p-tolyl/phenyl)siloxanes are soluble in toluene and chloroform at room temperature. Polydi(4-propylphenyl)siloxane crystallizes slowly, and if recovered and tested before becoming fully crystalline it will dissolve in common solvents such as toluene and chloroform at room temperature. However, after annealing it becomes soluble only at high temperatures. The cyclic trimer of di(o-tolyl)siloxane could only be prepared in trace quantities, and we were unsuccessful in preparing polydi(o-tolyl)siloxane, probably because of the steric interactions of the o-tolyl groups.

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The sorption of moisture by different cellulose derivatives was examined as a function of relative humidity, to evaluate the influence of counter-ions and different charged groups on the moisture adsorption mechanism. Studies were made on cellulosic materials containing sulfate (-O-SO3H) and carboxylic (-COOH) groups in different ionic forms (H ?, Li ?, Na ?, K + and Ca 2 ?). Uncharged cellulose and amylose were also examined for comparison. It was shown that the choice of counter-ions had a large influence on the moisture uptake by the studied polymers. Moisture adsorption by cellulose containing sulfate acid groups was favoured by the counter-ion H ?, rather than, in order of decreasing efficiency, by Li +, Na ?, Ca-" + and K ?. Two types of differently adsorbed water were found: non-freezing bound water and freezing bound water. Most of the differences in total moisture content were due to differences in the freezing water content. The counter-ion favouring water adsorption in the case of the cellulose containing carboxylic acid groups was Li ?, followed, in decreasing order of efficiency, by Na +, K +, Ca 2? and H ?. In this case, the differences in total water content were found in both the non-freezing and freezing water. It was furthermore shown that the presence of charged groups was necessary for the adsorption of freezing water when the relative humidity was less than 100%. The large influence of the counter-ions on water adsorption may be associated with the ionic radius (size of the counter-ion), which influences the degree of hydration. Differences in water adsorption for the protonated form may be explained by the observation that carboxylic acids are weak acids with limited dissociation, whereas the stronger sulfate acid groups facilitate a more complete dissociation.

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This work investigates the possibility of reducing the permeability of polystyrene by adding small amounts of a liquid-crystalline azo compound, 2,3-dimethyl-4-n-butyl-4-(4"-methoxybenzoyloxy)azobenzene (BMA). Addition of BMA to polystyrene can lead to either an increase or a decrease in permeability depending on the effects of BMA concentration and casting conditions on the film morphology. The film morphologies were characterized by polarized light microscopy, wide-angle X-ray diffraction and differential scanning calorimetry; following which the permeability of H2, N2, CO2 and water vapour were measured. Relative to polystyrene, 30-40% decrease in the composite permeability can be achieved with only 2% BMA loading. This decrease is due to the 'antiplasticization' effect of BMA on polystyrene.

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Organic-soluble optically transparent polyimides were prepared from alicyclic dianhydride monomer, bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA). BCDA gives soluble polyimides with diamines containing at least one flexible linkage such as ether, methylene and sulfide. The polyimides have glass transition temperatures above 350°C and a thermal decomposition temperature of 450°C in an inert atmosphere. The polyimides form a tough film with an ultra-violet cut-off between 300 and 400 nm, which is comparable to that of a fluorinated polyimide.

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The Flory-Huggins interaction parameter gsc~ was determined for chemically crosslinked poly(vinyl alcohol) (PVA) hydrogels from swelling pressure and elastic modulus measurements. The PVA gels were prepared in aqueous solutions of different molecular weight (22 000 < M, < 346 000). Crosslinks were introduced at different polymer concentrations (3% w/w ~< c o ~< 12% w/w). It is found that in all systems the values of Zgcl for the crosslinked polymer are greater than the values of X.~oJ for the uncrosslinked material at identical concentrations. The ggc, data reported here seem to be a function only of the polymer concentration and are independent of the details of the network structure. The results are discussed in relation to other work on the crosslink dependence and volume fraction dependence of ;(g,~.

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The two-stage drawing of uniaxially oriented poly(ethylene terephthalate) (PET) films has been undertaken, together with the drawing of films at constant width, which are biaxially oriented, under equivalent conditions of temperature and strain rate. From measurements of the changes in refractive index, drawing stress and peak shrinkage stress, it is concluded that the behaviour can in all cases be described by the deformation of a molecular network, which is of a very similar nature not only for all these present measurements but also for previous studies of PET fibres and films.

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New poly(imide-pyridazine-amide)s have been synthesized by the solution polycondensation of aromatic diamines containing preformed pyridazine rings with diacid chlorides which incorporate both imide and hexafluoroisopropylidene units. Solubility, thermal stablhty and electro-insulating properties of these compounds are discussed and compared with those of fluorinated poly(imide-amide)s which do not contain pyridazine rings, and also with those of other related heterocyclic polymers that have been previously reported

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In view of various contradictory theoretical equations relating the interfacial tension a between phase-separated polymer solutions to the Flory-Huggins interaction parameter of the system, the idea that a should depend on the extent of the 'hump' in the concentration dependence of the Gibbs energy of mixing was studied. This investigation is based on 12 series of ~r(T) measurements reported in the literature and on additional experiments for the system cyclohexane/polystyrene. To quantify the extent of the 'hump', a reduced 'hump energy' e. was introduced and its value calculated for different temperatures from the measured critical data of the systems. The analysis of the entire experimental material yields a scaling law of the form a= Er, r where F is close to 0.5 for all systems, in contrast to E which varies within a larger interval. Furthermore, e. is related to ~, the relative distance to the critical temperature, by e= AzB; B is approximately 2.4, again relatively independent of the system, in contrast to A. In case of trustworthy values of the scaling parameters, the above relations offer an interesting possibility to estimate a(T) from the sole knowledge of the critical temperature of the system.

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Axially oriented poly(ethylene terephthalate) fibres and films with widely differing processing histories were prepared by varying the spinning speed in the case of fibres and the speed, temperature, medium and extent of drawing for both fibres and films. The samples were held at constant length and heated to temperatures between 60 and 220°C with simultaneous recording of their thermomechanical response for up to 20 s. Samples produced at low speeds developed low shrinkage stress, which decayed with time. On the other hand, samples produced at relatively higher speeds developed higher shrinkage stress, which showed little relaxation with time. The structural basis of these results is discussed, and the roles played by processing parameters highlighted.

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The synthesis of a series of bis(ether anhydride)s with hindering substituents, especially t-butyl and methyl, has been developed using nucleophilic displacement reactions between nitrophthalodinitriles and substituted hydroquinones, bisphenols and a naphthalene dioi. The bis(ether anhydride)s have been successfully incorporated into poly(ether imide)s with hindering residues by polymerization with diamines, with and without aikyl substituents. The thermal and mechanical properties of a number of the polymers and their permeabilities to several gases have been determined. The properties of the polymers are discussed, along with those of related polymers. It is shown that the properties are strongly controlled by their structural features. In particular, the flexibilities of polymer backbones and substituents are found to influence glass transition temperatures and, in conjunction with the influence of chain rigidity on packing, to influence gas permeabilities and permselectivities.

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