Synthesis, characterization, and stability of carbodiimide groups in carbodiimide-functionalized latex dispersions and films

Abstract

Cyclohexylcarbodiimidoethyl methacrylate (CCEMA) and t-butylcarbodiimidoethyl methacrylate (t-BCEMA) were prepared in a two-step synthesis. These monomers were then used to prepare carbodiimide-functionalized PBMA and PEHMA latex particles, employing two-stage emulsion polymerization, with the carbodiimide–methacrylate monomers being introduced only in the second stage under monomer-starved conditions. During emulsion polymerization, the carbodiimide moiety (NCN) was found to be unstable at pH 4, but stable when the pH of the dispersion was increased to 8, using NaHCO3 as the buffer. Survival of NCN group against hydrolysis during the polymerization, and during storage in the dispersion, was enhanced by using EHMA as the comonomer (more hydrophobic) and the t-butyl carbodiimide derivative. The t-butyl group provides more steric hindrance to the hydrolysis reaction. A decrease in the reaction temperature from 80°C to 60°C was also found to increase the extent of NCN group incorporation during emulsion polymerization. Under ideal conditions, more than 98% of the NCN groups in the monomer feed are successfully incorporated into the latex. When these latex particles are mixed with a COOH containing latex and allowed to dry, polymer diffusion leading to crosslinking occurs. Films annealed at 60°C reach a gel content of 60% in 10 h. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 855–869, 2000