ABSTRACT:The phase structure of poly-(R)-(3-hydroxybutyrate) (PHB)/chitosan and poly-(R)-(3-hydroxybutyrateco-3-hydroxyvalerate) (P(HB-co-HV))/chitosan blends were studied with 1 H CRAMPS (combined rotation and multiple pulse spectroscopy).1 H T 1 was measured with a modified BR24 sequence that yielded an intensity decay to zero mode rather than the traditional inversion-recovery mode.1 H T 1 was measured with a 40-kHz spin-lock pulse inserted between the initial 90°pulse and the BR24 pulse train. The chemical shift scale is referenced to the methyl group of PHB as 1.27 ppm relative to tetramethylsilane (TMS) based on 1 H liquid NMR of PHB. Single exponential T 1 decay is observed for the ␤-hydrogen of PHB or P(HB-co-HV) at 5.4 ppm and for the chitosan at 3.7 ppm. T 1 values of the blends are either faster than or intermediate to those of the plain polymers. The T 1 decay of ␤-hydrogen is bi-exponential. The slow T 1 decay component is interpreted as the crystalline phase of PHB or P(HB-co-HV). The degree of crystallinity decreases with increasing wt % of chitosan in the blend. The fast T 1 of ␤-hydrogen and the T 1 of chitosan in the blends either follow the same trend as or faster than the weight-averaged values based on the T 1 of the plain polymers. Together with the observation by differential scanning calorimeter (DSC) of a melting point depression and one effective glass transition temperature in the blends, the experimental evidence strongly suggests that chitosan is miscible with either PHB or P(HB-co-HV) at all compositions.