Crystallinity and Miscibility of Poly(vinyl isobutyl ether)/Poly(ε-L-lysine) Blends by Solid State 13C NMR Study

The relation between crystallinity and miscibility of semicrystalline polymer blends of poly(vinyl isobutyl ether) (PVIBE) and poly(e-L-lysine) (e-PL) is investigated by 13C cross-polarization with magic-angle-spinning (CPMAS) NMR (nuclear magnetic resonance) and DSC measurements. Analysis of the 1H spin-lattice relaxation curves observed from both PVIBE and e-PL signals, which are indirectly obtained from well-resolved 13C CPMAS NMR spectra, suggested that the domains of e-PL in the blends are in the range of 50–100 nm scale. Two-spin or three-spin models were used to simulate the 1H relaxation curves taking into account the contribution of a 1H spin-diffusion rate between PVIBE and e-PL. Furthermore, it was found that blending e-PL largely influences the crystallinity of PVIBE but that of e-PL is little affected by blending PVIBE except for 10/1 composition. The observed melting point of e-PL shifted towards lower temperature accompanied by PVIBE content. This shift was explained by the Gibbs-Thomson effect that the decrease of thickness of crystalline phase causes the depression of the melting point.