Evaluation of castor acrylated monomer (CAM) as a comonomer for vinyl-acrylic latexes
Castor acrylated monomer (CAM) has been proposed for application as a comonomer in emulsion polymerization. CAM functions as a potent non-volatile plasticizer, improving latex film formation which reduces organic cosolvent requirements in latex coating formulations. CAM also possesses an internal isolated double bond which functionalizes latex polymers for auto-oxidative polymerization after application. Auto-oxidative functionality is provided only if the internal double bond is preserved during emulsion polymerization to synthesize the latex. CAM and its commercial version (COMCAM) were applied as emulsion polymerization comonomers in vinyl-acrylic latexes. A suitable formulation for vinyl-acrylic synthesis which provided high conversion and molecular weight rivaling commercial vinyl-acrylic latexes was established. A method for instantaneously correlating the conversion and reaction anomalies was developed through monitoring reaction exothermic profiles. 1 H and 13 C NMR assignments were made for CAM and several structural analogs of CAM: hydrogenated CAM (HCAM), castor acrylated butyl ester monomer (CAB), and castor acrylated 2-ethylhexyl ester monomer (CAEH). Establishing the correct NMR peak assignments is important for evaluating the copolymerizability of the castor derived monomers and the potential for oxidative reactivity of latex polymers containing them. A preferred method for emulsion polymerization was established involving staging the monomer addition to separate vinyl acetate monomer feed from castor oil derived monomer feed. Incorporation of CAM and COMCAM in vinyl-acrylic latexes was proven, and the level of preservation of the internal double bond was shown to be high. COMCAM/vinyl-acrylic synthesis is highly dependent on the surfactant system for achieving high conversion, COMCAM incorporation, as well as internal double bond preservation. The higher molecular weight CAM homologs present in COMCAM are more difficult to incorporate and are prone to phase separation when using an inadequate surfactant system.