BLENDS OF POLYAMIDE-6 AND SULFONATED POLYSTYRENE - A SOLID-STATE NMR-STUDY

Polymer blends of polyamide-6 (PA6) with polystyrene at 5.4 % and 9.7 % sulfonation levels (SPS5 and SPS10) were investigated by means of solid-state NMR techniques. In the measurement of proton spin-lattice relaxation of PA6 in the rotating frame, a double-exponential decay curve, corresponding to the relaxations of PA6 in the crystalline and the amorphous phases, was observed. When the blend was miscible with separated phases smaller than ca. 20 angstrom, the PA6 carbon magnetization displayed a single-exponential decay during the spin-lock time; the relaxation time was equal to that of polystyrene in the blend. It was found that the unfunctionalized polystyrene and the sodium salt of the sulfonated polystyrene were immiscible with PA6, but the lithium salt of the sulfonated polystyrene could be highly miscible with PA6 to such an extent that either the blend was completely homogeneous or the separated phases, if present, were smaller than ca. 20 angstrom. It is of particular interest that the miscibility of the blends of lithium sulfonated polystyrene and PA6 is dependent on the polymer ratio and the sulfonation level. Among the LiSPS5/PA6 and LiSPS10/PA6 blends at ratios of 70:30, 50:50, and 30:70, only the blends at 70:30 are highly miscible with separated phases smaller than ca. 20 angstrom. However, the blends at other polymer ratios are all miscible on the scale of ca. 200 angstrom, based on the measurements of proton spin-lattice relaxation in the laboratory frame. In combination with DMTA data, we conclude that the dimensions of the separated amorphous phases are between 50 and 200 angstrom for the LiSPS5/PA6 50:50 and 30:70 blends, while for the LiSPS10/PA5 50:50 and 30:70 blends they are between 20 and 100 angstrom. Annealing at 140-degrees-C induced the formation of a PA6 crystalline phase in the LiSPS5/PA6 70:30 blend, while it had a minimum effect on the LiSPS10/PA6 70:30 blend.