Humidity sensitive properties of quaternary ammonium salts containing polyelectrolytes crosslinked with 2-oxazoline crosslinker

New 2-oxazoline group-containing copolymer crosslinkers for humidity-sensitive polyelectrolytes were prepared by copolymerization of [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (METAC), 2-isopropenyl-2-oxazoline (IPO) and n-butyl methacrylate (BMA). They were mutually crosslinkable with carboxylic acid-containing copolymers METAC/acrylic acid (AA)/BMA = 10/2/8. When the polyelectrolytes were applied to the humidity-sensitive membranes, the resistance varied from 107 to 103 Ω between 20% RH and 95% RH, which was required for a humidity sensor operating at ambient humidity. Temperature dependence, hysteresis, response time, water durability and long-term stability at high humidity were also measured and estimated.