Orientation in solid polymers

Polymers Chain dynamics Local viscosity in polymer environments Molecular orientation in solid polymers Migration of excitation energy along polymer chains... 

Because chromophores orientation is important for creating anisotropy and optical nonlinearities, intensive studies have been performed to understand induced molecular orientation and relaxation processes in polymers. To gain further insight into the physics of thin polymer films and the effects of molecular orientation in solid polymers, studies at high pressure could be beneficial. Pressure as a thermodynamic parameter is widely used to study... 

A number of methods are available for the determination of the degree of molecular orientation in solid polymers. Techniques that selectively give information about the molecular orientations in the crystalline and amorphous regions are especially valuable. A potential method for measurement of orientation is the determination of the CSA. 

Pulsed deuteron NMR is described, which has recently been developed to become a powerftd tool for studying molectdar order and dynamics in solid polymers. In drawn fibres the complete orientational distribution function for the polymer chains can be determined from the analysis of deuteron NMR line shapes. By analyzing the line shapes of 2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. In addition, motional heterogeneities can be detected and the resulting distribution of correlation times can directly be determined. 

Wilkes, G. L. The Measurement of Molecular Orientation in Polymeric Solids. Vol. 8, pp. 91-136. Williams, G. Molecular Aspects of Multiple Dielectric Relaxation Processes in Solid Polymers. Vol. 33, pp. 59-92. 

The fluorescence polarization technique is a very powerful tool for studying the fluidity and orientational order of organized assemblies (see Chapter 8) aqueous micelles, reverse micelles and microemulsions, lipid bilayers, synthetic non-ionic vesicles, liquid crystals. This technique is also very useful for probing the segmental mobility of polymers and antibody molecules. Information on the orientation of chains in solid polymers can also be obtained. 

We have intended to demonstrate that a flaw spectrum analysis presents a plausible and useful approach to the problem of multiple flaw failure phenomena in solid polymers. Effects of orientation and stress state may be explained by such an approach, but much additional theory and experiments are required to establish the validity of the method. Several obvious shortcomings of the theory can be overcome, in principle, by a more rigorous analysis. The more serious assumptions or limitations which we intend to either remove or justify in future work are as follows. 

Ward, J. M., 5th Europhys. Conf. MacromoL Phys., Orientation effects in solid polymers, p. 1-26. Budapest,. April 27-30, 1970... 

Orientational order plays an important role in solid polymers. It is often induced by industrial processing, for example in fibers and injection- or compression-modulated parts. In polymers with liquid-crystalline properties of the melt or solution, the anisotropies generated by the flow pattern are particularly pronounced. In order to improve the mechanical properties of polymer fibers or films, the degree of orientation is intentionally enhanced by drawing. At the same time, anisotropy of mechanical properties can result in low tolerance to unfavourably directed loads. In many liquid-crystalline polymers, in the mesophase near the transition to the isotropic phase, electric or magnetic fields can induce macroscopic orientational order [1]. Natural polymers such as silk protein fibers, which are biosynthesized and spun under biological condition, also have good mechanical properties because of their ordered structure [2]. 

The effect of structural memory in a wave field has been exsemplarily studied by the IR-spectroscopy method on films made from mixtures of butadiene-styrene and acrylic latex as models of polymeric membranes. The strengthening of the interphase interaction in heterophase systems that can cause change of their local and transmitting mobility has been observed. It has been shown, that the response of polymeric dispersed systems and compositions on influence of nonlinear vibrations proves their influence on deformation properties, like orientation phenomena in solid polymers (where Rebinder s effect can take place) that it is possible to consider as a way of polymer modifications, including the obtaining of nanicomposites, polymeric biocarriers, etc. 

It is generally accepted that the solid state polymerization of BCMO initiated with y-radiation proceeds by a cationic mechanism. Typical radical inhibitors affect neither the rate nor the final yield of polyBCMO. On the basis of the dependence of the polymer yield on the size of monomer crystals and the observed high degree of orientation in the polymers, it was originally suggested that the structure of the monomer crystal lattice directly imposes order and orientation upon the polymer 35>. 

Si, P) have also been used to probe the structures, conformations, phase behavior, and orientations of solid polymers. In this regard, the N NMR observations of crystalline nylons by Murthy and co-workers [51, 52] and the Si NMR observations of the thermo- and piezochromic polysilanes by Schilling and co-workers [53-58] are particularly noteworthy. In chapter 6, many of the same high resolution techniques are used to probe the mobilities of polymer chains in solid samples. 

The free-radical reactions in solid polymers in the presence of NO are of particular significance for the preparation of spin-labelled polymers. This method has become particularly important for chemically inert, rigid and insoluble polymers, for instance, polytetrafluoroethylene (PTFE), because of the difficult problem of introducing spin labels by chemical reactions of nitroso compounds, nitrons or nitroxyl biradicals [31], Oriented PTFE films y-irradiated at room temperature in air after prolonged NO exposure contain nitroxyl radicals whose ESR spectra are displayed in Figure 3 [32],... 

Shear controlled orientation in injection moulding (SCORIM) is based on the progressive application of macroscopic shears at the melt-solid interface during solidification in the moulding of a polymer matrix. 

---