One- and Two-Dimensional CP/MAS 13C NMR Analyses of Dynamics in Poly(2-hydroxypropyl ether of bisphenol-A) (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Dynamic Characterisitics)

Abstract

The dynamics of amorphous poly(2-hydroxypropyl ether of bisphenol-A) (PHR), quenched from the melt, has been investigated by one- and two-dimensional solid-state 13C NMR spectroscopy. CP/MAS 13C NMR spectra from .150 to 180 oC give two specific features: (1) below 23 oC, resonance lines for CH carbons of phenylene rings split into two lines; (2) linewidths of resonance lines become broad at 20 - 50 oC above the glass transition temperature. The feature (1) indicates that phenylene C-H carbons exist in chemically different two sites at low temperatures. These two sites are probably associated with OH … hydrogen bond formation. The coalescence of the resonance lines at elevated temperatures is caused by flip motion of phenylene rings, which corresponds to the relaxation for PHR. The correlation time of the flip motion is analyzed by the two-site exchange model, and is found to follow the Arrhenius equation. The apparent activation energy is 51 kJ mol-1 by assuming an inhomogeneous correlation time distribution described by a Kohlrausch-Williams-Watts (KWW) function with an exponent of 0.2. The feature (2) is caused by the so-called motional broadening, which is originated by enhanced segmental motions. This dynamics corresponds to the relaxation for PHR and can be described by William-Landel-Ferry (WLF) equation. Two-dimensional CP/MAS 13C exchange NMR experiments confirm the existence of flip angle distribution as well as the distribution of correlation times of phenylene ring flip motion with a KWW exponent of 0.2.