Phase transition from a C-centered to a B-centered orthorhombic crystalline form of syndiotactic poly(propylene)

✍ Scribed by Finizia Auriemma; Russell H. Lewis; Hans Wolfgang Spiess; Claudio De Rosa

• Book ID: 102939208
• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 666 KB
• Volume: 196
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/macp.1995.021961212

✦ Synopsis

Abstract

Samples of highly syndiotactic poly(propylene) (s‐PP) crystallized in a C‐pseudo‐centered orthorhombic form are here characterized through high resolution solid state ^13^C NMR sepctroscopy and wide angle X‐ray diffraction. The ^13^C NMR CP MAS (cross‐polarization, magic angle spinning) spectra of highly disordered quench‐precipitated s‐PP samples (with a structure very close to a C‐pseudo‐centered orthrohombic form) yield additional resonances beside those already reported in the literature for s‐PP samples crystallized with the chains in a fully helical \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} (TTGG\rlap{--} )_n $\end{document} conformation (T: trans; G: gauche). From the correlation of ^13^C NMR CP MAS spectra with the X‐ray diffraction profiles recorded at the same temperatures, it is possible to establish that at a given temperature (approximately 100°C, for our samples) a phase transition from the C‐ to the B‐pseudo‐centered orthorhombic form starts to occur. Correspondingly, the aforementioned additional resonances in the ^13^C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the ^13^C NMR CP MAS spectrum of samles crystallized in the B‐pseudo‐centered structure. NMR and X‐ray diffraction data, according to differential scanning calorimetry, were interpreted with a recrystallization phenomenon; at temperatures below 140°C for our samples, the variously sized C‐pseudo‐centered orthorhombic crystallites melt and readily re‐crystallize in the B‐pseudocentered orthorhombic form.