Orientation, solid-state process effect

The Effect of Orientation by Solid State Processes on the Amorphous Regions in Poly(yinyl alcohol) and High Density Poly(ethylene)... 

An extrusion technique that has siowiy been gaining popuiarity is solid-state extrusion. The polymer is forced through a die while it is below its melting point. This causes substantial deformation of the polymer in the die, but since the polymer is in the solid state, a very effective molecular orientation takes place. This orientation is much more effective than the one which occurs in conventional melt processing. As a result, extraordinary mechanical properties can be obtained. 

Nuclear magnetic resonance (NMR) spectroscopy is a most effective and significant method for observing the structure and dynamics of polymer chains both in solution and in the solid state [1]. Undoubtedly the widest application of NMR spectroscopy is in the field of structure determination. The identification of certain atoms or groups in a molecule as well as their position relative to each other can be obtained by one-, two-, and three-dimensional NMR. Of importance to polymerization of vinyl monomers is the orientation of each vinyl monomer unit to the growing chain tacticity. The time scale involved in NMR measurements makes it possible to study certain rate processes, including chemical reaction rates. Other applications are isomerism, internal relaxation, conformational analysis, and tautomerism. 

There is a point when the NMR characteristics of a bulk polymer have to be treated as non-liquid-like, that is below the glass transition temperature. The NMR spectrum will then be dominated by static effects, such as the orientation dependence of chemical shift and the dipolar interaction. The earliest forms of solid-state polymer NMR were developed in the knowledge that these solid-state effects would be present, and would complicate the resulting data interpretations. Proton NMR studies of polymers have an impressive pedigree, and have relied on applications of a distinct solid-state theory. But it is only relatively recently that aspects of this theory have been refined to the point where experimental observations can be understood more fully. In particular, the process of spin diffusion is much better appreciated. Proton broad-line NMR does not necessarily require the use of large magnets and despite the theoretical uncertainties it has been widely accepted within the realms of rapid analysis. In its simplest form it has been used to quantify liquid and solid ingredients, for example, in plasticised polymers. 

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