Molecular dynamics of the spin probes in dry and wet poly(3-hydroxybutyrate) films with different morphology

The molecular mobilities of the spin probes TEMPO and TEMPOL in microbial poly(3-hydroxybutyrate) (PHB) have been studied by the ESR method in a range of temperatures from 293 to 363 K. The spectra of the dry and wet films with isotropic and textured morphology are analyzed as a spectral superposition of the "fast-" and "slow-rotating" fractions. Nonpolar TEMPO is sensitive to structural heterogeneity and practically nonsensitive to water sorption. The polar TEMPOL can interact with the carbonyl groups of PHB and the ESR spectra are affected by water molecules. The differences of spectral characteristics between the textured and isotropic PHB films are manifested in the rotation mobility (rotation correlation times) and the mole fractions of the "fast-" and "slow-rotating" ESR probes. Comparison of ESR data with water diffusivities in the textured and isotropic samples reveals the relationship between transport phenomena and morphology of the novel biopolymer material. (C) 2000 Elsevier Science Ltd. All rights reserved.