Scattering Studies of Cyrstallization in Highly Oriented Polymers

The solidification of low molecular weight materials from their melts (in the absence of temperature fields) generally leads to a product with no preferred orientation, independent of the extent or rate of deformation of the melt. The solidification of polymers from a highly deformed melt or solution nearly always leads to a product with preferred molecular orientation. Further, the rate of solidification can be significantly increased by melt deformation. The change in rate, relative to that in a quiescent melt or solution, can be several orders of magnitude [1]. These differences, relative to small-molecule systems, arise from the degree to which orientation and local strain can be maintained in the melt. Due to the long-range connectivity within a polymer molecule, it is possible to impart large extensions to these molecules in the molten state, and significant time is often required for the molecules to relax back to their undistorted, coiled state. If crystallization or glass formation occurs before the chain can relax, an extended molecular configuration can be retained. Thus in the solidification of oriented polymers there exists a competition between the “freezing” of the molecular orientation and the relaxation (re-coiling) of the molecules.