Humidity Sensitive Properties of Restructural Films Prepared from Polymer Latex with Carboxylic Acid Functional Groups

The polymer latex of poly(butyl acrylate (BA)-acrylic acid (AA)) was synthesized by soapless seeded emulsion polymerization or soapless emulsion copolymerization. The morphology of the composite polymer latex synthesized by soapless seeded emulsion polymerization was core-shell structure. The humidity-sensitive polymer films were made by the melting of the polymer latex at 68°C followed by chemical modification with aqueous solution of NaOH. The glass transition temperature (Tg) of poly(butyl acrylate) (PBA) is below room temperature (−54°C), so PBA has flexible behavior at the room temperature. The humidity-sensitive properties of the flexible polymer films were investigated. The core—shell polymer latex with either linear core or crosslinked core was synthesized. The polymer latex that had the crosslinked core was melted to form polymer films with crosslinked domains. The polymer latex that had the linear core was melted to form the polymer films with linear structure. It is confirmed that polymer films with crosslinked domains had larger humidity sensitivity and less hysteresis than polymer films with linear structure. The effect of multiple use on the humidity sensitivity of the polymer films with crosslinked domains was insignificant. For polymer films with crosslinked structure or poor flexibility, the degree of humidity sensitivity increased with temperature. The humidity sensitivity may decrease with increase of temperature for flexible films.