An infrared spectroscopic approach to the polymophic behavior of syndiotactic polyropylene and its crystal-crystal transformations during mechanical stretching

摘要

This paper depicts an infrared study of the molecualr structure and orientation of the different polymophic conformations of syndiotactic polypropylene(sPP) under conditions of stress.A sample of sPP predominately in the helical form is subjected to mechanical stress and the use of infrared spectroscopy permits the detailed investigation of the transformations that take place.in particular,when the sample of sPP was exposed to strain under constant velocity at room temperature,helical form I was transformed to the trans-planar Form III.The subsequent relaeease of the tension causes the sample to shrink and to revert to its initial helical conformation.This transformation is also accompanied by an increase in the dichroism fo theinfrared active bands as a consequence of polymer orientation in the stretching direction.When the sample of sPP was subjected to a step-wose stretching procedure at room temperautre,the formation of a striated pattern consisting of transparent and opaque bands was observed,a phenomenon which is known as "the trans-planar structure.in addition,the "necking"region which is formed at the beginning of the procedure at slow strain rates exhibits an equally high orientation.