Preparation and Properties of Thermo-sensitive Latex Films

Abstract

Polymer particles with hydrophobic core and hydrophilic shell were prepared via a three-step method. First, poly (butyl methacrylate –co- methyl methacrylate) (p-(BMA-MMA)) latex was prepared through emulsion polymerization. Then, using the p-(BMA-MMA) latex as seed, a uniform shell of poly(glycidyl methacrylate) (p-GMA) was formed by using a redox initiation system under kinetically controlled conditions. The contents of the shell were in the range of 5-15 wt. %. Finally, the epoxy groups existing in the shell were converted into the ionic species through the reaction with triethanolamine hydrochlorid in aqueous phase, resulting in a charged hydrophilic shell. The solid particles could be re-dispersed in water to afford a stable emulsion. Latex films were prepared by spin-casting the aqueous mixture of the latex made from the solid latex particles and poly (vinyl alcohol) (PVA) onto an aluminum substrate and then dried at room temperature. The contact angles between the core-shell latex films and water were in the range of 16.1°−27.5° at 25 °C, but would turn to be larger than 87° after the films were baked at 150 °C for a short period of time. This indicated that the films were completely switched from hydrophilicity to hydrophobicity by the action of heat. Additionally, the latex films before baking could be easily washed away from the substrate with neutral water, but could no longer be removed after baking. When an IR dye (with maximal absorption at 830nm) was incorporated into the film, the film became sensitive to LD lasers emitting at 830 nm and negative images were obtained after exposed by LD laser and developed by neutral water.