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 p oly(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 wi th isotropic and textured morphology are analyzed as a spectral superpositi on of the "fast-" and "slow-rotating" fractions. Nonpolar TEMPO is sensitiv e to structural heterogeneity and practically nonsensitive to water sorptio n. The polar TEMPOL can interact with the carbonyl groups of PHB and the ES R spectra are affected by water molecules. The differences of spectral char acteristics between the textured and isotropic PHB films are manifested in the rotation mobility (rotation correlation times) and the mole fractions o f the "fast-" and "slow-rotating" ESR probes. Comparison of ESR data with water diffusivities in the textured and isotrop ic samples reveals the relationship between transport phenomena and morphol ogy of the novel biopolymer material. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.