Oriented crystallization in fiber formation: Inferences from the structureand properties of melt spun syndiotactic polypropylene filaments

In processes, such as melt spinning, the crystallization behavior of syndio tactic polypropylene (sPP) is found to be substantially different from that of most other linear polymers. The anisotropic stress field in such proces ses leads invariably to extension as well as alignment (orientation) of the chains in the melt, both of which contribute usually to dramatic enhanceme nt in the rate of crystallization. However, since the primary structure of the sPP chain in its most preferred crystal form is comprised of a "coiled helical," -(T(2)G(2))(2)-, sequence, stress-induced chain extension can lea d to conformational sequences that are not favorable for crystallization in this form. As a consequence, process conditions that generate higher stres s levels can cause a diminution in the rate of crystallization of this poly mer. Such conformation-related aspects of oriented crystallization of sPP h ave been addressed through an analysis of the structure and properties of m elt-spun fibers, produced over a range of spinning speeds. The results serv e to identify a refinement that is needed in current models of oriented cry stallization and also a mechanism to promote the nucleation of crystallizat ion of sPP. (C) 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81:2305-2317, 2001.