Synthesis of liquid crystalline polyurethane elastomers from zinc complex and aliphatic diisocyanate

Abstract

Polyurethane elastomers containing hexadentate Schiff base zinc complex in the polymer chains have been synthesized. Prepolymers were synthesized from the reactions between hexamethylene diisocyanate and different dialcohols, including polycaprolactone diol, polycaprolactone triol and polypropylene glycol. Isocyanate contents in the prepolymers were determined by titration. The prepolymers were then subjected to polymerization with hexadentate Schiff base zinc complex to yield polyurethane elastomers. The progress of polymerization reaction was monitored by using infrared spectroscopy. The disappearance of isocyanate peak at 2270 cm⁻¹ was observed when the polymerization was completed. Liquid crystalline property and morphology of the polymers were examined by using polarizing optical microscope and scanning electron microscope, respectively. The result showed that the suitable isocyanate contents in HDI/PCL diol prepolymer, HDI / PCL triol prepolymer and HID / PP glycol prepolymer for the preparation of polyurethane were 17%, 13% and 55%, respectively and the weight content of zinc complex in the resulting polyurethanes were 9%, 10% and 16% respectively. The polymer showing the brightest birefringence which was due to liquid crystallinity was PCL triol polyurethane.