Conformation analysis and molecular mobility of ethylene and tetrafluoroethylene copolymer using solid-state 19F MAS and 1H → 19F CP/MAS NMR spectroscopy

✍ Scribed by Keitaro Aimi; Shinji Ando

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 578 KB
• Volume: 42
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1391

✦ Synopsis

Abstract

The changes in the conformation and molecular mobility accompanied by a phase transition in the crystalline domain were analyzed for ethylene (E) and tetrafluoroethylene (TFE) copolymer, ETFE, using variable‐temperature (VT) solid‐state ^19^F magic angle spinning (MAS) and ^1^H → ^19^F cross‐polarization (CP)/MAS NMR spectroscopy. The shifts of the signals for fluorines in TFE units to higher frequency and the continuing decrease and increase in the T~1ρ~^F^ values suggest that conformational exchange motions exist in the crystalline domain between 42 and 145 °C. Quantum chemical calculations of magnetic shielding constants showed that the high‐frequency shift of TFE units should be induced by trans to gauche conformational changes at the CH~2~CF~2~ linkage in the E–TFE unit. Although the ^19^F signals of the crystalline domain are substantially overlapped with those of the amorphous domain at ambient probe temperature (68 °C), they were successfully distinguished by using the dipolar filter and spin‐lock pulse sequences at 145 °C. The dipolar coupling constants for the crystalline domain, which can be estimated by fitting the dipolar oscillation behaviors in the ^1^H → ^19^F CP curve, showed a significant decrease with increasing temperature from 42 to 145 °C. This is due to the averaging of ^1^H^19^F dipolar interactions originating from the molecular motion in the crystalline domain. The increase in molecular mobility in the crystalline domain was clearly shown by VT T~1ρ~^F^ and ^1^H → ^19^F CP measurements in the phase transition temperature range. Copyright © 2004 John Wiley & Sons, Ltd.