Poly(O-acyl-hydroxy-L-proline) IV. Studies of Molecular Motions in Poly(O-acetyl, butyryl, hexanoyl, dodecanoyl, and benzoyl-hydroxy-L-proline) Films by the Spin Probe Technique

Abstract

The molecular motion in poly(O-acetyl (Ac), butyryl (But), hexanoyl (Cap), dodecanoyl (Lau), and benzoyl (Bz)-hydroxy-L-proline (Hyp)) films was investigated by ESR measurements with 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl (TEMPO) as the spin probe. As the length of acyl side chains increased, the temperature at which the separation of the outer extrema of ESR spectra reached 50 gausses (T50) decreased. The rotational correlation times (τc) obtained from the ESR spectra at −70°C for series of polymers were nearly the same. The values of τc at 130°C decreased with an increase in the acyl side chain length until the number of carbon atoms in the acyl chains reached 6. The activation energies of TEMPO in the polymers were less than 3 kcal mol−1 at low temperatures. At high temperatures, the activation energies of poly(O-Ac-Hyp) and poly(O-Bz-Hyp) differed scarcely from those at low temperatures. The activation energies of poly(O-But-Hyp), poly(O-Cap-Hyp), and poly(O-Lau-Hyp) were enhanced and particularly that of poly(O-Cap-Hyp), exceeding 10 kcal mol−1.