Journal of Polymer Science Part A: Polymer Chemistry, Vol.38, No.5, 855-869, 2000
Synthesis, characterization, and stability of carbodiimide groups in carbodiimide-functionalized latex dispersions and films
Cyclohexylcarbodiimidoethyl methacrylate (CCEMA) and t-butylcarbodi-imidoethyl 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 degrees C to 60 degrees 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 degrees C reach a gel content of 60% in 10 h.
Keywords:poly(n-butyl methacrylate);poly(ethylhexyl methacrylate);emulsion polymerization;cyclohexylcarbodiimidoethyl methacrylate;t-butylcarbodiimidoethyl methacrylate;latex