Molecular dynamics of poly(3-hydsoxybutyrate) studied by the spin probe technique

The molecular mobility of poly(3-hydroxybutyrate) (PHB) was studied in the temperature interval from 20 to 90 degrees C by EPR using stable nitroxyl r adicals 2,2,6 6-tetramethyl-1-peridinyloxy (Tempo) and 4-hydroxy-2.2,6,6-te tramethyl-1-piperidinyloxy (Tempol) as spin probes. Two series of PHB sampl es, prepared by different methods, possessed isotropic and textured morphol ogies. The noncrystalline phase of PHB contain regions of two types with ma rkedly different molecular mobilities. It is suggested that "dense" regions , characterized by a comparatively low mobility of polymer chains, are loca ted near the surface of crystalline grains, while the "loose" (amorphous) r egions with a higher mobility of chains are more distant from the surface o f grains. Molecular mobility in the dense regions was virtually the same fo r both isotropic and textured PHB samples, whereas the mobility in the loos e regions was lower in the isotropic samples than in the textured ones. Sat uration of the polymer with water vapor affected both the mobility of polym er chains and the relative content of loose and dense regions in the sample s.