Dielectric dispersion and conductivity of moisture-containing amorphous polymers

The effect of the moisture content in amorphous polymers (PS, PVC, PMMA) on their electro-physical properties is considered. Analytical relationships describing the inflence of the external-field frequency and environmental relative humidity on the conductivity of the polymers are given. For the use of these polymers as active elements of moisture sensors, the moisture-resistive effect is estimated.     

Birefringence dispersion in oriented polystyrene

The dispersion of birefringence in oriented amorphous polymers is discussed. It is shown that for polystyrene, the birefringence can be considered as the product of an orientation function and a function of the wavelength of the light. This leads to a method for expressing the birefringence dispersion as a function that is characteristic of the polymer. This function is determined for polystyrene, and from it the birefringence at infinite wavelength is found to be 11% lower than that measured with the mercury green line (5461 A.).     

Dielectric relaxation time of polymers

The temperature dependence of the dielectric relaxation time of amorphous polymers can be described quite satisfactorily by an expression derived from the theory of the relaxation time for local conformational transitions in a polymer chain. This theory was recently developed using the Kramers theory of the rate constant together with the free-volume theory.     

Elliptical dichroism of oriented helical polymers

A linear response theory of elliptical dichroism is obtained for light propagating perpendicular to the helix axes of a system of oriented helical polymers by solving the equation of motion for the radiation field's average vector potential. A nonlinear mixture of circular and linear dichroism and birefringence is obtained.     

Crystallization of polymers in oriented state

Summary Summarizing a number of experiments concerning crystallization of polymers in oriented state, and attempting to compare them with predictions of various theories one comes to the conclusion, that in many areas of the field the experimental results remain in qualitative agreement with theory. It is much difficult to find such agreement concerning quantitative aspects. The reason for that comes from both sides; experiments are usually made at conditions, which do not correspond to theoretical assumptions, and theories usually discuss particular models, which are not able to describe full variety of morphologies and situations occurring in reality.It is believed that measurements performed at constant stress will provide data, that could be used to verify some theories. Basing on these data, it should be also possible to predict behaviour in other, more complex conditions. This is the matter of practical importance, and finally it could give better insight into phase transition occurring in such processes like fiber spinning, film blowing or injection molding, at each of them the molecular orientation takes place.Also explanation of morphological peculiarities appearing in oriented crystallization, as well as deeper insight into crystallization mechanisms can be expected from this type of measurements.

---

With 12 figures     

Thermal conductivity of oriented crystalline polymers

Thermal conductivities of six oriented semicrystalline polymers which range from 0.37 to 0.63 in crystallinity and 1 to 5 in draw ratio λ (up to about 15 for two polymers) have been measured between 100 and 340 K. It was found that for increasing λ the conductivity K_∥ (along the draw direction n?) increases rapidly while K_⊥ (normal to n?) decreases slightly; K_∥ also increases with temperature, but K_⊥ shows no simple pattern in temperature dependence. These general features can be reproduced reasonably well at low draw ratio (λ < 5) by the modified Maxwell model, and the discrepancy in details may be attributed to the fact that the model does not take into account the possible anisotropy of the amorphous phase of the oriented polymers. At high draw ratio the intercrystalline bridge effect becomes important, and one must resort to the Takayanagi model, but the lack of corroborating x-ray data has rendered a detailed comparison impossible.     

Two-photon dispersion in conjugated polymers

The frequency dependence of the dispersive and absorptive parts of a strongly allowed two-photon transition is determined in a series of conjugated polymer solutions. The data analysis yields the energy and width of the two-photon transition, symmetry assignment for the two-photon transition (A_g → A_g), and oscillator strengths for both the one-photon and two-photon transitions.     

Formation of kink bands in oriented polymers

The circumstances of the formation of kink bands have been investigated with a newly designed shearing device and light and electron microscopes. Kink bands having sharp edges and reflection symmetry about the edges were formed and studied in the two crystalline polymers, high-density polyethylene and isotactic polypropylene, but could not be formed in the two glassy polymers, poly(4,4′-dioxydiphenyl-2,2-propane carbonate) and poly(2,6-dimethylphenylene oxide). The characteristics of the oriented polymer that promote kink bands seem to be easy slip along the orientation axis, and resistance of the oriented fibrils to length changes. Kink bands were found to initiate at sites of shear stress concentration, where the fibrils are first deformed into an S-shaped curve, that then tightens and finally collapses into kinks.     

Quantitative molecular characterization of oriented semi-crystalline polymers

The stress-strain birefringence relations obtained from the hot drawing of poly(ethylene terephthalate) films are analysed within the framework of non-Gaussian models of rubber elasticity. It is found that, in spite of the increasing influence of strain-induced crystallization for higher draw ratios, the proposed treatment of experimental results leads to the definition of the number of statistical links per elastic chain in the amorphous part of the sample for any state of elongation. The results suggest a progressive disentanglement of the physical network structure and make possible an evaluation of the limit of extensibility attainable in cold-drawing.     

Small angle scattering of partially oriented polymers

Summary A general method for the calculation of the small angle scattering pattern of partially oriented polymers with rotational symmetry about the fiber axis is explained. The method can be used with widely varying models for the basic scattering unit.

---

Zusammenfassung Es wird eine allgemeine Methode zur Berechnung des Kleinwinkelstreudiagramms von partiell orientierten Polymeren mit Rotationssymmetrie bezüglich der Faserachse angegeben. Als Modell für die streuende Grundeinheit können die verschiedensten Strukturen verwendet werden.

     

Dielectric properties of polymers based on hexafluoropropylene

Dielectric measurements have been made at frequencies from 10 Hz to 100 kHz and temperatures from 4 K to at least 300 K on a number of polymers containing units of hexafluoropropylene (HFP). These included copolymers of tetrafluoroethylene (TFE) and HFP, the homopolymer of HFP, elastomeric copolymers of HFP and vinylidene fluoride, and alternating copolymers of methyl vinyl ether with TFE and HFP. The effect of an ether linkage between the CF₃ group and the chain was also considered. Most of these polymers exhibited a main chain local mode relaxation near 228 K and a side group relaxation near 93 K.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayWe appreciate the helpful discussions with W. W. Schmiegel.     

The spectral dispersion curves of highly oriented fibres

Spectral dispersion curves of the refractive indices and birefringence of highly oriented fibres [poly(ethylene 2,6-naphthalene-dicarboxylate) (1000 denier/248 filaments, PEN-Q50M4; PEN), poly(ethylene terephthalate) (PET), Seun yarn (meta-aramid fibres, Teijin Japan; CONEX) and Technora T-240 (1000 denier/667 filaments aramid fibres, Teijin Japan; TECHNORA)] have investigated using the automatic variable-wavelength interferometric (VAWI) technique. This technique is especially recommended for measuring the refractive indices of highly oriented fibres. The polarizabilities per unit volume are calculated for these fibres and the molecular orientation function of PEN and PET are determined. Microinterferograms are given for illustration.     

Groundstate dispersion interaction between pi-conjugated polymers

The line-dipole approximation is used to investigate the scaling of the groundstate dispersion interaction, EW, between parallel conjugated polymers of length L and transverse separation D. Both a second-order perturbation theory calculation using the Mott-Wannier exciton model of excited states and a semiclassical analysis of distributed dipoles indicate that at L approximately D there is a crossover from the point-dipole approximation result of EW approximately L2/D6 for LD.     

Dielectric anisotropy in oriented poly(chlorotrifluoroethylene)

Dielectric measurements between ?50 and 60°C have been made on isotropic and oriented samples of poly(chlorotrifluoroethylene) with draw ratios λ of 1 to 3.5 at frequencies ranging from 30 Hz to 1 MHz. For the oriented samples, the dielectric loss has been measured with the electric field normal (ε) and parallel (ε) to the draw direction. At low frequency (say 60 Hz) the loss data for the oriented samples reveal two peaks at 25 and ?5°C, which are associated with the amorphous (γ_a) and the crystalline (γ_c) relaxations, respectively. Analysis of these data using a two-phase model yields values for the amorphous orientation function f_a which are only about 25 to 60% of those for the crystalline orientation function f_c. Upon annealing, the anisotropy ε/ε at the γ_a peak decreases significantly while that at the γ_c peak remains largely unchanged. This implies a roughly unaltered f_c and a large decrease in f_a, which is consistent with the results of wide-angle x-ray diffraction and birefringence measurements.