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Phase transition from a C‐centered to a B‐centered orthorhombic crystalline form of syndiotactic poly(propylene)
Author(s) -
Auriemma Finizia,
Lewis Russell H.,
Spiess Hans Wolfgang,
De Rosa Claudio
Publication year - 1995
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.1995.021961212
Subject(s) - tacticity , orthorhombic crystal system , polymer chemistry , phase transition , phase (matter) , polymer science , materials science , chemistry , crystallography , crystal structure , organic chemistry , polymer , physics , condensed matter physics , composite material , polymerization
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.