Uniaxially stretched polymer

Chain relaxation processes of uniaxially stretched polymer chains an infrared dichroism study... 

Fig. 8.1. (a) Orientation of a typical structural unit in the sample coordinate frame XqYoZo where Z is the draw direction of a uniaxially stretched polymer (b) orientation of the sample in the laboratory frame XYZ where Z denotes the direction of Bq and Zq is the sample draw direction. 

Investigations of some of the elastic constants of uniaxially stretched polymers were made on nylon 66 and polyethylene terephthalate by... 

L. A. Rotenhurg, S. L, Mesophase Formation in Crosshnked PolydiethylsUox-anes Under Uniaxial Stretching. Polym. Sci. U.S.S.R. 1988,30,329-335. 

ABSTRACT - Fluorescence polarization and its application to orientation measurements of uniaxially stretched polymers are described. Results obtained on anthracene labelled polystyrene chains embedded in normal polystyrene and stretched at various temperatures and strain rates are presented and discussed. An improvement of the Doi-Edwards slip-link model is required to account for the results and a modified model is proposed. Finally, an illustration of fluorescence polarization measurements on mobile and oriented polyisoprene networks is shown. 

The studies reported above on the orientation of uniaxially stretched polymer melts show that fluorescence polarization is a very powerful technique to investigate the molecular behaviour. 

We carried out thermodynamic studies on the crystallization from melts of flexible-chain polymers uniaxially stretched at various degrees of molecular orientation in the melt and studied the effect of the stretching stress on thermodynamic parameters such as degree of... 

The parameters K1/ K2/ and K3 are defined by the refractive indices of the crystal and sample and by the incidence angle [32]. If the sample has uniaxial symmetry, only two polarized spectra are necessary to characterize the orientation. If the optical axis is along the plane of the sample, such as for stretched polymer films, only the two s-polarized spectra are needed to determine kz and kx. These are then used to calculate a dichroic ratio or a P2) value with Equation (25) (replacing absorbance with absorption index). In contrast, a uniaxial sample with its optical axis perpendicular to the crystal surface requires the acquisition of spectra with both p- and s-polarizations, but the Z- and X-axes are now equivalent. This approach was used, through dichroic ratio measurements, to monitor the orientation of polymer chains at various depths during the drying of latex [33]. This type of symmetry is often encountered in non-polymeric samples, for instance, in ultrathin films of lipids or self-assembled monolayers. 

R > is the mean square end-to-end distance of the polymer chain. Consider a sample stretched by a factor Ay in the Y direction and Az in the Z direction. A general deformation can be easily treated, but for simplicity only uniaxial stretching or isotropic swelling will be examined. Note that under conditions of uniaxial deformation, the volume of the sample changes very little. This change may be ignored, and it becomes convenient to set Az = A and Ax — Ay. ... 

The first SANS experiments on end-linked elastomers with a well-defined functionality were carried out by Hinkley et al, (22). Hydroxy-terminated polybutadiene was crosslinked by a trifunctional isocyanate, and the resultant polymer was uniaxially stretched. 

Many semicrystalline polymers are polymorphic and exist in different crystal forms. When PBT fiber is uniaxially stretched [75], the contracted gauche-trans-gauche a-crystal chain is extended to a fully trans conformation of a y-crystal. Above 20% strain, the crystal form is 100% y-crystal with a longer c-axis triclinic cell dimension. Thus, it is reasonable to ask whether the... 

The extruded fiber is then often uniaxially stretched by take-up rollers rotating at different speeds. The fiber stretching encourages the polymer chains to align on a molecular level producing increased strength in the direction of the pull. 

A second class of polarizers uses dichroism to produce linearly polarized light. Techniques to produce dichroic polarizing sheets were pioneered by Land [52], These are made by dissolving a strongly dichroic, small molecule into an amorphous, transparent polymer. The dichroic molecules are then oriented by a uniaxial stretching of the polymer matrix. Since this is accomplished below the polymers glass transition temperature, this ori-... 

Y. Zhao, B. Jasse, and L. Monnerie, Orientation and relaxation in uniaxially stretched poly(methyl methacrylate)-poly(ethylene oxide) blends, Polymer, 30, 1643 (1989). 

By contrast, the ECP must have conjugated rigid-rod macromolecules. Several such polymers show high electrical conductivity (usually after doping), viz. polyacetylene (PAc), polyaniline (PANI), polypyrrole (PPy), polyparaphenylenes (PPP), or poly-3-octyl thiophene (POT). The resins are expensive, difficult to process, brittle and affected by ambient moisture, thus blending is desirable. For uniaxially stretched fibers the percolation threshold is 1.8 vol%, hence low concentration of ECP (usually 5-6 vol%) provides sufficient phase co-continuity to ascertain conductivity similar to that of copper wires (see Table 1.79). 

PREPARATIVE TECHNIQUES Thermal conversion of a soluble precursor polymer in oxygen free atmosphere.Uniaxial stretch during thermal process yields highly anisotropic PPV films. 

---