FTIR spectroscopic investigation of thermal effects in semi-syndiotactic polypropylene

Michael S. Sevegney, Rangaramanujam M. Kannan, Allen R. Siedle, Pamela A. Percha

Research output: Contribution to journalArticlepeer-review

Abstract

The temperature-dependent behavior of individual components within metal-locene-catalyzed semisyndiotactic polypropylenes (semi-sPP) with a wide range of stereo-regular content (26 to 96% rr) is studied using Fourier transform infrared (FTIR) spectroscopy and temperature-modulated differential scanning calorimetry (DSC). Changes in sensitive, high-resolution absorbance spectra are observed as melt-slow-cooled thin films are subjected to stepwise temperature increases. In general, spectral bands previously identified as being sensitive to ordered structures (e.g., conformed chains, crystal morphs) appear to follow overall trends of shifting to lower wavenumbers (energies), broadening, and decreasing in peak area intensity as temperature increases. Peaks that appear due to "splitting" (observed in more stereoregular materials) show a trend toward coalescence as temperature increases; this corresponds to a gradual loss of chain conformational order. Gauche-gauche-trans-trans (ggtt) n helical and all-irons (tttt) n planar zigzag-conformed chains that participate in the crystalline-amorphous interfacial region ("mesophase") appear to be more stable (i.e., they do not lose their conformational order as easily) with increasing temperature in materials with a greater degree of syndiotacticity. Moreover, IR data correspond well with modulated DSC endotherms located near 50°C and 70°C. At each transition temperature - thought to represent, respectively, a thermally driven chain conformation from planar zigzags to helices, and a dynamic disorder of helices marked by rapid gauche ↔ trans isomerization - the IR absorbance ratio, A 978/Ag 963, which represents the relative population of helical chains, undergoes an accelerated decrease.

Original languageEnglish (US)
Pages (from-to)439-461
Number of pages23
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume43
Issue number4
DOIs
StatePublished - Feb 15 2005
Externally publishedYes

Keywords

  • FT-IR
  • Metallocene catalysts
  • Structure-property relations
  • Syndiotactic polypropylene (PP)
  • Thermal properties

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Polymers and Plastics
  • Materials Chemistry

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