Production of colloidally stable latices from low molecular weight ethylene-propylene-diene copolymers

The best impact modifiers for coatings and engineering plastics include fixed morphol. core-shell particles. For the present work, ethylene-propylene copolymers (EPM) and ethylene-propylene-diene copolymers (EPDM) were chosen, for their good resistance to stringent conditions, like UV-irradn. or high temps., to prep. the core of the desired particles. The soln.-emulsification technique was used to produce artificial latices based on low mol. wt. EPM and EPDM materials. Conventional emulsification techniques as well as miniemulsification' methods have been investigated. In both cases, a larger vol. of polymer is reduced into smaller sub-units using the mech. energy of comminution techniques, i.e. an Ultra-Turrax and a homogenizer operating at a pressure of 300 bar and with a shear rate of approx. 3.2*107 s-1. The difference between conventional emulsification and miniemulsification resides in the stabilizing system. For the conventional emulsification method, an equimolar mixt. of anionic (sodium dodecyl benzene sulfonate, SDBS) and nonionic (polyoxyethylene (100) stearyl ether, Brij 700) surfactants was found to be the optimal surfactant system. For the miniemulsification method, a combination of SDBS as surfactant and hexadecane or cetyl alc. as costabilizer was the most suitable system. Both conventional emulsification and miniemulsification lead to latices with monomodal particle size distributions and vol.-av. diams. ranging from 300 to 400 nm, detd. with light scattering techniques. The low mol. wt. elastomers, exhibiting viscosities lower than 1 Pa s at 20 Deg, were easily emulsified without addn. of org. solvent.