Monitoring elasticity and orientation in syndiotactic polypropylene

Gautam Parthasarathy, Michael S. Sevegney, Rangaramanujam M. Kannan

Research output: Contribution to journalArticlepeer-review

Abstract

The effect of temperature on the elasticity and structure of syndiotactic polypropylene (sPP) is investigated using a combination of WAXD and rheo-optical FTIR spectroscopy. sPP has a rich crystal structure, which leads to unique mechanical behavior. Beyond yield point, it exhibits elastic response associated with deformation-induced structure-structure transformation. The structure and orientation were measured both during and after uniaxial tensile stretching of films (up to 200%) as a function of temperature (25-70 °C). Our WAXD and rheo-FTIR results suggest that as the temperature increases, there is a reduction in the extent of helical to trans-planar conformational change upon stretching. When the strain is released, there is partial transformation of trans-planar conformation back to helical. The presence and orientation of the trans-planar conformation plays a key role on the elastic behavior of sPP beyond the yield point. Rheo-optical FTIR dichroism studies provide further insights into the elasticity in syndiotactic polypropylene. Different proportions of helical and trans-planar conformations orient to different extents. The helical conformation does not orient appreciably at higher temperature though they are present beyond the yield point. In contrast, the trans-planar chains show a significant increase in dichroism beyond the yield point, suggesting that there is a difference in mobility (orientation) of the helical and trans-planar chains. This further supports the importance of trans-planar chains on the elastic behavior.

Original languageEnglish (US)
Pages (from-to)6335-6346
Number of pages12
JournalPolymer
Volume46
Issue number17
DOIs
StatePublished - Jul 28 2005
Externally publishedYes

Keywords

  • Elasticity
  • Rheo-optical FTIR dichroism
  • Syndiotactic polypropylene

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Materials Chemistry

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