1994 рік

Blends of ~t-methyl styrene/acrylonitrile copolymers with styrene/acrylonitrile copolymers and with styrene/maleic anhydride copolymers are shown to exhibit regions of miscibility that appear to depend rather sensitively on component molecular weights. These blends did not exhibit lower or upper critical solution temperature phase behaviour. A refined set of monomer unit pair interaction energies are given that reasonably describe the experimental results in terms of the Flory-Huggins theory

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Poly(vinylidene fluoride) and vinylidene fluoride-tetrafluoroethylene copolymers cocrystallize depending on the structures present in each. In the or-phase, the maximum difference in the defect concentration of the two polymers (A defect) equals 12.3% during isothermal crystallization, and is equal to 10.5% when the system is quenched. In the/y-phase, it is 1 !.8% for isothermal crystallization, and ~ 5.5% when quenched. Apart from isomorphic cocrystallization between components of the same polymorph, cocrystal formation between the :t- and /y-polymorphs was also observed. The resulting cocrystal adopts the structure of a particular polymorph, according to the results obtained from potential energy calculations. The interplanar spacings (dhkt) of the :t-phase of PVF 2 do not change with the H-H defect concentration, but for the/y-phase d2oo increases with the defect concentration. The reason for this difference in behaviour has been attributed to the more compact nature of the fl-polymorph unit cell, when compared to that of the ct-polymorph. The limiting value of the A defect for cocrystallization in the or-phase has been attributed to the larger difference in the intramolecular potential energy, whereas that of the/Y-phase has been attributed to the compact nature of the unit cell

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Two main-chain rigid-rod-like polyesters containing pendent t-butyl ester groups were synthesized. Simultaneous thermogravimetric analysis and Fourier-transform infra-red spectroscopy were applied to monitor the formation ofisobutylene as well as other gaseous products that evolved at elevated temperatures. The polymers were also characterized by microscopy, differential scanning calorimetry and infra-red spectroscopy before and after thermal treatment

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In the estimation of thermodynamic equation-of-state parameters, the ratio of contact sites of polymer segment and solvent molecule (s2/sO is an important quantity to be determined. In this work we have evaluated this ratio by using a novel method of approximation. For this purpose, we have arbitrarily changed the value of s2/s ~ and obtained the most suitable value yielding Z2 =0.303 by interpolation.

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In this paper we report the thermal and mechanical characterization of poly[bis(4-benzylphenoxy)- phosphazene] (PBPP). Glass transition and melting temperatures of 13.8 and 88.2°C respectively, and heat of fusion of 7.0 J g i were measured by differential scanning calorimetry (d.s.c.) for the as-synthesized polymer. Crystallization studies from the melt, in both isothermal and dynamic regimes, showed a low crystallizability of PBPP, due to the high mobility and steric hindrance of lateral substituents, with a heat of fusion no higher than 9 J g-1. Activation energies of about 70 kJ mol-1 were calculated both for the crystallization process and for the rubber-glass transition in the amorphous state. The highest crystallization rate in isothermal experiments occurred at a temperature of 45°C. Thermodegradation of PBPP in air was found to start with the probable formation of the hydroperoxide group on the methylene site at about 233°C, as demonstrated from both thermogravimetric and d.s.c, analyses. PBPP film behaved as an elastomeric polymer with a strain at break higher than 350%. A tensile modulus of 1.2 MPa and a stress at break of 4.8 MPa for the amorphous polymer were measured, whereas crystalline polymers exhibited higher tensile modulus and stress at break, ranging from 34 to 48 MPa and from 7 to 12 MPa, respectively.

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Gas permeability coefficients for several gases (He, CO2, CH4, 0 2 and N2) were measured at 25°C in a series of semicrystalline diblock copolymers of polyethylene/poly(ethylene-propylene)A. simple model is presented describing the gas transport in these polymer systems. It predicts the permeability of a randomly oriented spherulitic diblock specimen from the values of the permeability coefficients of the individual lamellar regions of the copolymer. Model predictions were in excellent agreement with the experimental data. The upper bound (lamellae aligned in parallel with respect to the permeation direction) and lower bound (series lamellar alignment) models were calculated and compared to a limited amount of corresponding experimental data on oriented specimens

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Thermoreversible polymer gel electrolytes with ionic conductivities in the region of 10-3 S cm-1 (even at -20°C) have been prepared from a variety of commercially available polymers and organic solvents by gel casting from high-temperature solutions at polymer/solvent ratios down to 10/90. Lithium trifluoromethanesulfonate has been incorporated as the ionic species necessary for conduction. A typical gel has polymer/solvent in mass ratio 40/60 and has salt incorporated to give an active O/Li ratio of 12/1. In general, the dynamic modulus (G') of these gels is in excess of 10 s Pa at low strain, but decreases rapidly with increasing strain amplitude despite remaining approximately constant with strain rate. This drop in modulus, which is attributed to breakdown of the gel network, is completely recoverable. In particular, one polymer, poly(vinylidene fluoride), was studied in detail. Gels made from this polymer formed self-supporting transparent films. The incorporation of lithium trifluoromethanesulfonate changed the crystal structure and decreased the solvent evaporation rate, at elevated temperatures, of poly(vinylidene fluoride) gels made with tetraethylene glycol dimethyl ether. Ionic conductivities of liquid electrolytes (dimethylformamide with lithium trifluoromethanesulfonate) and corresponding gels (dimethylformamide, lithium trifluoromethanesulfonate and poly(vinylidene fluoride)) suggest that there is no interaction between salt and polymer in these gels, although this is still under investigation

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Some simple experiments have been carried out to assess the kinetics of the radical polymerizations of vinyl ethyl, vinyl tert-butyl, vinyl phenyl and vinyl benzyl carbonates at temperatures between 30°C and 60°C. It is shown that, contrary to some impressions given in the literature, the vinyl alkyl carbonates can be polymerized readily to give polymers of high molecular weight with conventional radical initiators (i.e. benzoyl peroxide and azoisobutyronitrile) provided that it is recognized that they polymerize relatively slowly owing, probably, to them having relatively low values of kp/klt/2. Therefore radical initiators must be used with these monomers at temperatures at which they will have relatively long half-lives. It is further shown that the low-temperature initiator, dicyclohexylperoxydicarbonate (DCHPC), favoured by previous workers for the polymerization of these monomers, offers no obvious advantages over the use of the more conventional initiators at higher temperatures, and that an alternative low temperature initiator, tert-butylperoxyneodecanoate, polymerizes vinyl alkyl carbonates with a facility equal to that of DCHPC

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The phase behaviour of poly(2-chlorostyrene)/poly(vinyl methyl ether) blends (P2CS/PVME) was investigated by means of light scattering and small-angle X-ray scattering (SAXS) using synchrotron radiation. It was found that P2CS/PVME blends possess a lower critical solution temperature. Chemically labelling P2CS with photoreactive anthracene not only decreases the miscibility of the blends but also shifts the critical point of the phase diagram towards a composition higher in P2CS - a typical effect of such systems with polydispersity induced by the labelling reaction. Within the temperature range of the experiments, the critical behaviour of both unlabelled and labelled blends can be accurately expressed by the mean-field theory with the critical exponents v = 1/2 and V = 1. These experimental results suggest that the effects of chemical labelling of polymer chains via polymer reactions may play an important role in the phase decomposition kinetics and morphological studies of polymer blends

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The traditional view of epitaxial growth of a crystal on an underlying substrate, having appropriate lattice matches, is that the growth proceeds immediately and that nucleation considerations are unnecessary. In the case of substrates having limited dimensions, it is necessary to ensure that the dimensions of the critical secondary nucleus do not exceed the dimensions of the substrate crystal. It is shown that this condition is very important when polymeric substrates are used. In essence, there is a necessity for the elementary growth 'template' of the depositing polymer to fit the elementary existing lamellar template of the substrate. For the case of polyethylene growing on a polypropylene substrate, it is shown that a simple theory explains all the known facts and resolves a current controversy involving epitaxy versus nucleation for that system.

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