Modification of Natural and Artificial Polymer Colloids by 'Topology-Controlled' Emulsion Polymerization

A diffuse layer of water-soluble polymer chemically grafted to the surface of a hydrophobic polymer colloid has been created by the second-stage polymerization of dimethylaminoethyl methacrylate (DMAEMA) onto the biomacromolecule polyisoprene in natural rubber latex and also onto synthetic polybutadiene and polystyrene latexes. To control the locus of radical formation, the process was initiated by a redox couple wherein one component (e.g., cumene hydroperoxide) is hydrophobic and the other (e.g., tetraethylenepentamine) is hydrophilic. The modified latexes displayed a dramatic increase in colloidal stability at low pH which is attributed to grafted hydrophilic polymer acting as an electrosteric stabilizer; the effect is particularly remarkable in natural rubber latex, which usually has poor colloidal stability for pH 8. 13C NMR was performed to verify the existence of the grafted copolymer and to quantify yield. The mechanism by which such a novel morphology can be generated is postulated to be via a process of radical formation at the particle surface followed by the subsequent grafting to the hydrophobic polymer backbone and polymerization of hydrophilic monomer in the aqueous phase. This technique is potentially useful for creating novel materials from natural rubber latex.