Anchoring of polyelectrolyte membrane containing chalcone group to electrode substrate by [2+2] cycloaddition and its humidity-sensing properties

New chalcone group-containing acrylic copolymers were prepared by the copolymerization of [3-(acrylamido) propyl]trimethyl ammonium chloride (APTAC), methyl methacrylate (MMA), and 4-methacryloyloxyphenyl styryl ketone (MPSK) for use as humidity-sensitive polyelectrolytes. The copolymers were self-crosslinkable terpolymers with different contents of APTAC /MMA/MPSK=70/27/3, 70/25/5, 70/23/7, and 70/20/10. Pretreatment of an alumina substrate with 4,4′-bis(3-triethoxysilyl)propoxy chalcone (BTSPC) containing an alkoxysilane-coupling agent was performed to attach the humidity-sensitive polyelectrolyte to it through covalent bonds. The sensors were irradiated with UV light, causing the electronically excited chalcone molecules to undergo a crosslinking reaction via [2π + 2π] addition. After soaking in water for 24 h, the resulting sensor using BTSPC showed water durability and a 42∼65% increase in resistance, corresponding to a 2.25∼2.98%RH decrease in relative humidity. The sensor showed good hysteresis (−0.2%RH), an acceptable response time (80 sec) and good stability at high temperatures and humidity.