2D NMR Observation of Strain-Induced β-Form in Poly[(R)-3-hydroxybutyrate

Abstract

The first NMR observation of the planar zigzag conformation (β-form) in a poly[(R)-3-hydroxybutyrate] uniaxially oriented film with high tensile strength is reported. A 13C two-dimensional (2D) off-magic-angle spinning NMR method which directly correlates the peak positions with the molecular orientation in uniaxially oriented samples was used. The 2D NMR spectra provide the 13C carbonyl signal of β-form separately from that of the 2/1 helix conformation (α-form). The orientations of the carbonyl carbons for α-form and β-form were determind and compared to the previously proposed molecular models.