Humidity-sensitive properties of a cross-linked polyelectrolyte prepared from mutually reactive copolymers

Two mutually reactive three component copolymers were synthesized to utilize as humidity-sensitive membranes. The major ingredient of a humid membrane is the cross-linked polyelectrolyte obtained from the copolymers 4-vinylpyridine (VP)-(methacryloxyethyl) trimethylammonium chloride (METAC)-n-butyl acrylate (BA) = 1 : 2 : 1, 2 : 2 : 1, 2 : 3 : 1 and 3 : 2 : 1, and 2-chloroethyl acrylate (CEA)- METAC-BA = 1 : 2 : 1, 2 : 2 : 1, 2 : 3 : 1 and 3 : 2 : 1. The humidity sensor prepared from the reaction of VP-METAC-BA = 3 : 2 : 1 with CEA-METAC-BA = 3 : 2 : 1 showed average impedance of 620, 41.9 and 3.38 kOmega at 30, 60 and 90% relative humidity humidity (RH), respectively. Temperature dependence, frequency dependence and response time were measured. The variation of humidity on temperature between 5 and 35 degreesC was -0.62 to -0.67% RH degreesC(-1) and the hygrometric hysteresis between humidification and desiccation processes were less than +/- 2% RH. The humidity sensors using polyelectrolyte cross-linked were quite resistant to water.