Miscibility and morphology of chiral semicrystalline poly‐(R)‐(3‐hydroxybutyrate)/chitosan and poly‐(R)‐(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/chitosan blends studied with DSC, 1H T1 and T1ρ CRAMPS

The phase structure of poly‐(R)‐(3‐hydroxybutyrate) (PHB)/chitosan and poly‐(R)‐(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (P(HB‐co‐HV))/chitosan blends were studied with ¹H CRAMPS (combined rotation and multiple pulse spectroscopy). ¹H T₁ was measured with a modified BR24 sequence that yielded an intensity decay to zero mode rather than the traditional inversion‐recovery mode. ¹H T_1ρ 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 ¹H liquid NMR of PHB. Single exponential T₁ decay is observed for the β‐hydrogen of PHB or P(HB‐co‐HV) at 5.4 ppm and for the chitosan at 3.7 ppm. T₁ values of the blends are either faster than or intermediate to those of the plain polymers. The T_1ρ decay of β‐hydrogen is bi‐exponential. The slow T_1ρ 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_1ρ of β‐hydrogen and the T_1ρ of chitosan in the blends either follow the same trend as or faster than the weight‐averaged values based on the T_1ρ 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. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1253–1258, 2002