Morphological evolution of multistage polymer particles in the alkali post-treatment

Multistage carboxyl-containing polymer latex particles were synthesized by multistep emulsion copolymerization using methyl methacrylate (MMA), butyl acrylate (BA), methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA) and styrene (St) as raw materials, and the latex particles with diverse morphologies including multihollow, hollow and “bowl-like” were obtained by post-treating the multistage latex particles under alkali condition. The morphological evolution of the particles in the alkali post-treatment process was characterized with electron microscopy, and effects of alkali treatment conditions including treatment temperature, time as well as initial pH on particle morphology were investigated. Results indicated that the alkali treatment temperature and initial pH were the key parameters to control the morphology of the treated particles. When the alkali treatment temperature was below 60 °C or the initial pH was lower than 8.5, the particle morphology was almost unchanged no matter how long the treatment time was prolonged. The multihollow and hollow particles could be formed as alkali treatment temperature exceeded 60 °C in the range of initial pH from 8.8 to 9.5. While the latex particles with “bowl-like” morphology were observed when the multistage latex was alkali treated at 90 °C for 3 h with initial pH 9.8. Furthermore, extending alkali treatment time was beneficial to get the swelling equilibrium of the latex particles.