The effects of boric acid on the phase stability of poly(1-oxotrimethylene) solutions in the aqueous solution of ZnCl2, CaCl2, and LiCl

Abstract

The effects of boric acid on the phase stability of poly(1-oxotrimethylene) (ECO) solutions in the aqueous solution of zinc chloride, calcium chloride, and lithium chloride were investigated. The intrinsic viscosity of the ECO solutions was increased by addition of boric acid, implying the improvement of ECO solubility. It was ascribed to the supporting role of boric acid on the polarization of the zinc-water ligand complex in the solutions. The dynamic viscosity (η'), storage modulus, and loss modulus at 0.05 rad/s of the 7 wt% ECO solutions containing boric acid were increased with increasing boric acid content at 70 oC. The loss tangent (tanδ) at 0.05 rad/s and the slope of the Cole-Cole plot of the solutions were increased with increasing boric acid content up to 1.0 wt%, followed by the decrease above that content, indicating that the introduction of 1.0 wt% of boric acid showed the most remarkable effects on improving the homogeneity among the contents we observed. The addition of 1.0 wt% of boric acid significantly retarded the time-dependent change of rheological properties for 8 hrs, whereas the ECO solutions without boric acid showed a notable time-dependence such as increase of η' and decrease of tanδ in lower frequency range by aging at 70 oC. In addition, time-dependent increase of the yield stress and decrease of the slope of the Cole-Cole plot of the solutions suggested the deterioration of the homogeneity. The reduced viscosity of 0.5 g/dl ECO solutions without boric acid was decreased by aging, suggesting the shrinkage of the polymer coil. In UV-Vis spectra, the time-dependent increase of absorbance at 390 nm represented the generation of complex in the ECO solutions, whereas the disappearance of the absorbance by addition of boric acid confirmed the suppression effects of boric acid on the complex formation.