The thermal and mechanical properties and the ionic conductivity of cationic polyurethane elastomers with pendant trimethylammonium group

Abstract

A series of cationic polyurethane (PU) elastomers with pendant ammonium group, different polyether chains, and different content of ionic groups were prepared by nonsolvent technique. NCO-terminated prepolymers were prepared from 2,4-tolylene diisocyanate and polyols including poly(oxytetramethylne)glycol (PTMG) and poly(oxypropylene) glycol (PPG). Cationic PU elastomers were prepared by the reaction of prepolymer with the mixture of chain extenders [1,1,1-trimethylolpropane, 2-ethyl-2-methyl-1,3-propanediol, and cationic diol, 3-trimethylammonium-(1,2-propanediol)iodide]. The properties of cationic PU elastomers were studied regarding the effect of polyol type, ion content, and ion site by means of differential scanning calorimetry, dynamic mechanical thermal analysis, tensile testing, and complex impedance measurement. As the ion content increased, the demixing of hard segment from PTMG soft segment proceeded. PTMG-rich soft micro-phase became purer but its quantity decreased. The trend was reduced for PPG-based PU elastomers. While PU elastomers with ammonium group in pendant have micro-multiphase structure, PU elastomers with that in backbone have approximately homogeneous structure. The ionic conductivity was about 10-10 S cm-1 at room temperature and 10-7 S cm-1 at 100°C. The effects of micro-phase separation on the conductivity of cationic PU elastomers were discussed. Temperature dependence of conductivity obeyed Vogel-Tamman-Fulcher equation.