G.R. Davies

Dynamic mechanical behaviour and longitudinal crystal thickness measurements on ultra-high modulus linear polyethylene: a quantitative model for the elastic modulus

Abstract In this paper the dynamic mechanical behaviour of ultra-high modulus polyethylene is reported. The results are discussed in terms of a fibre reinforced composite model, in which the amount of fibre phase is related to the number of intercrystalline bridges determined from X-ray diffraction data. For both drawn and extruded materials a good correlation has been obtained between the plateau modulus at −50°C and the longitudinal crystal thickness. This correlation is given a quantitative interpretation in terms of the model and the increase in modulus with increasing deformation ratio is ascribed to an increase in continuity of the crystalline phase. The increase in tensile modulus on cooling through the γ-process is related primarily to the change in the tensile modulus of the amorphous phase. The fall in modulus at high temperature, on the other hand, indicates a fall in the shear modulus of the crystalline phase, which provides a satisfactory explanation of the α-process.

Ionic conductivities of poly(methoxy polyethylene glycol monomethacrylate) complexes with LiSO3CH3

Abstract Ionic conductivity values for LiSO3CF3 complexes with two amorphous poly(methoxy polyethylene glycol monomethacrylates) (PEM) were determined and values as high as ∼6 × 10 −4 Ω −1 cm −1 at 373 K and ∼2 × 10 −5 Ω −1 cm −1 at 293 K were achieved. These values are compared with those obtained for a poly(ethylene oxide) (PEO)-LiSO3CF3 complex of similar salt concentration with an ether oxygen to Li+ ion ratio of 18. The conductivity results for the complexes are similar at temperatures >343 K but at 293 K the values for the conductivities of the PEM-LiSO3CF3 complexes are approximately two orders of magnitude higher than those for the PEO-LiSO3CF3 complex. This difference is believed to be due at least in part to the presence of a large amount of crystalline material in the PEO-LiSO3CF3 complex below 323 K.

Ionic conductivities for poly(ethylene oxide) complexes with lithium salts of monobasic and dibasic acids and blends of poly(ethylene oxide) with lithium salts of anionic polymers

Abstract Lithium salts of two polyanionic addition polymers containing alkyl sulphonic acid and perfluoroalkyl carboxylic acid side groups were prepared. Blends of these polymers were formed with poly(ethylene oxide) (PEO). The blend containing alkyl sulphonate units showed some phase separation but this was not observed for the blend containing perfluoroalkyl carboxylate groups. In the latter case a comparatively high conductivity of ∼10 −5 Ω −1 cm−1 at 374 K was obtained. The anionic units in these blends are expected to be virtually immobile. Complexes formed from PEO and the Li-salt of hexafluoroglutaric acid had similar high ionic conductivities and there are grounds for supposing that the anions in these complexes may also be substantially immobilized. In addition, conductivity values were obtained for some PEO complexes containing lithium salts of some monobasic acids and it was found that the complex formed from the Li-salt of the strongest acid gave the highest conductivity ( ∼4 × 10 −4 Ω −1 cm−1 at 373 K for a PEO-LiSO3CF3 complex).

Statics and dynamics of model dendrimers as studied by molecular dynamics simulations

Molecular dynamics simulations were performed for a series of AB2 dendrimer models, in explicit-solvent solutions where the ratio Rg/L (Rg is the radius of gyration and L the size of the simulation box) is kept between 0.15⩽Rg/L⩽0.2. Results on static properties (size, shape, density profiles) are in good agreement with recent theoretical and experimental studies. Dynamic properties are systematically investigated on the local and entire molecule length scale. The dynamic characteristics of the examined models capture the qualitative behavior observed experimentally in dendrimer molecules. The systematic and comparative nature of this study affords detailed insight into the origin and the relative contribution of different relaxational mechanisms in the observed dynamic spectra.

Dynamic mechanical properties of random copolyesters of 4-hydroxybenzoic acid and 2-hydroxy 6-naphthoic acid

Abstract The dynamic mechanical moduli have been determined in tension and torsion for oriented thermotropic liquid crystalline polymers formed by copolymerization of 4-hydroxybenzoic acid and 2-hydroxy 6-naphthoic acid. The behaviour has been interpreted in terms of an aggregate model of units of structure. On this basis the fall in tensile modulus with increasing temperature can be quantitatively related to two factors, a decrease in the intrinsic chain modulus and a reduction in the shear modulus.

Ionic conductivity and viscosity correlations in liquid electrolytes for incorporation into PVDF gel electrolytes

The correlation between ionic conductivity and viscosity in liquid electrolytes formed by the dissolution of lithium triflate in N,N-dimethyl formamide and tetraethylene glycol dimethyl ether has been investigated. These liquid electrolytes may be incorporated in polymer gel electrolytes based on poly(vinylidene fluoride). The use of the Walden product to investigate ionic interactions is discussed.

Determination of molecular orientation by polarized infra-red radiation in an oriented polymer of high polarizability

Abstract A quantitative treatment is presented for the absorption of polarized infra-red radiation at normal incidence by a transversely isotropic polymer film. In addition to the reflectivity correction, an approximate treatment of the internal field problem is also carried out. This is important where the polymer is of high polarizability. It is shown how the orientation and concentration of the absorbing species can be derived from experimental data.

Experimental and theoretical longitudinal chain moduli of copolymers of hydroxybenzoic acid with 2-hydroxy-6-naphthoic acid

Abstract The changes with stress of the meridional X-ray scattering patterns from liquid crystalline copolymers of hydroxybenzoic acid with hydroxynaphthoic acid have been used to measure the average chain moduli. The values obtained have been compared with theoretical estimates of the chain moduli and in general found to be greater than the latter at low temperatures. It is concluded that, although an isolated chain has a comparatively low modulus, in the polymer environment the need to overcome intermolecular shear forces results in an enhancement of the modulus. The importance of the shear modulus in determining sample properties is discussed and the conformational implications for the copolymer molecules are examined.

Hysteresis of the stress-induced crystalline phase transition in poly(butylene terephthalate)

Abstract The stress-induced crystalline phase transition in poly(butylene terephthalate), (4GT), has been investigated by X-ray diffraction and laser Raman spectroscopy. A well defined stress hysteresis effect has been demonstrated and a continuum theory has been developed which satisfactorily describes the temperature dependence of the phenomenon.

Thermoreversible polymer gel electrolytes

Abstract 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 105 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.