Unexpected Crosslinking During Acetoacetoxy Group Protection on Waterborne Crosslinkable Latexes

Summary: The microstructure of the polymer synthesized by seeded semicontinuous emulsion copolymerization of AAEMA was investigated. It was found that the neutralization of the latexes with ammonia to protect acetoacetoxy functionality against hydrolysis during storage had a remarkable effect on the gel content. A base catalyzed Michael addition reaction between acetoacetoxy groups and terminal double bond (TDB) is proposed as responsible for the chain precrosslinking observed. The presence of TDB in the latexes was demonstrated by means of ¹H NMR. Moreover, the chain precrosslinking affected the subsequent crosslinking reaction of the latex with diamines hindering chain interdiffusion and yielding poorer mechanical properties.

Michael addition between AcAc functional groups and TDB, and final gel content of the MMA/BA/MAA latexes with different amounts of AAEMA.