Preparation and morphological characterization of two- and three-component natural rubber-based latex particles

Abstract

Different emulsion polymerization processes allowed variation in the microstructure of composite natural rubber (NR)-based latex particles. A prevulcanized and a not-crosslinked natural rubber latex were coated with a shell of crosslinked poly(methyl methacrylate) (PMMA) or polystyrene (PS). The bipolar redox initiating system tert-butyl hydroperoxide/tetraethylene pentamine promoted a core-shell arrangement. Furthermore, PS subinclusions were introduced into the NR core. The initiators used for the subinclusion synthesis were azobisisobutyronitrile at high temperature and a redox initiation system consisting of tert-butyl hydroperoxide/dimethylaniline at low temperature. The morphology of the resulting latex interpenetrating networks (IPN) was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Different staining methods allowed us to increase the contrast between the NR phase and the secondary polymers in the composite latex particles. A semicontinuous feeding process decreased the PS subinclusions size by a factor of 6 in comparison with a batch reaction. Depending on the NR/styrene swelling ratio, the crosslinking degree, and the polymerization temperature used, distinct differences of the phase arrangement of polymers in the latex particles were revealed.