ISSN:
1022-1352
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Samples of highly syndiotactic poly(propylene) (s-PP) crystallized in a C-pseudo-centered orthorhombic form are here characterized through high resolution solid state 13C NMR sepctroscopy and wide angle X-ray diffraction. The 13C 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 13C 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 13C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the 13C 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.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1995.021961212
Permalink
