Preparation in presence of urushiol and properties of acrylate latex with interparticle bridges

Acrylate latices were prepared by seeded emulsion polymerization of methyl methacrylate (MMA) and butyl acrylate (BA) in presence of urushiol with multifunctional groups (0–6 wt%). The emulsion polymerization was strongly influenced by the urushiol content. With increasing urushiol content, the conversion rate of the monomers first increased then decreased, the stability of emulsion polymerization gradually declined, the average particle size of the latex increased from 115.9 to 175.3 nm, and a change from mono- to bimodal particle size distribution occurred. Interestingly, transmission electron microscopy (TEM) showed that some particles were connected by linear bridges in presence of urushiol. Based on results of ¹H nuclear magnetic resonance (NMR) analysis, such formation of interparticle bridges is due to participation of urushiol in the emulsion polymerization of the acrylate monomers. The content of urushiol also affected the properties of latex films. With increasing urushiol content from 0 to 3 wt%, the adhesion, pencil hardness, and contact angle were markedly improved from grade 6 to grade 2, from B to 3H, and from 22° to 61°, respectively, due to formation of interparticle bridges. When the content of urushiol exceeded 3 wt%, the adhesion and pencil hardness remained unchanged, but the water contact angle markedly declined because of higher surface roughness of the latex film. Furthermore, addition of urushiol enhanced the thermal stability of the latex films.