Styrene/4-hydroxystyrene random, block and gradient copolymers modified with an organic dye: Synthesis by controlled radical polymerization and characterization of electrorheological properties

Styrene/4-hydroxystyrene block and gradient copolymers containing the organic dye Disperse Red 1 (S/HSDR) were synthesized using nitroxide-mediated controlled radical polymerization, and a random copolymer was made using conventional free radical polymerization. The three types of S/HSDR copolymer, with similar molecular weight and composition but different S/HSDR sequence distributions along each copolymer chain, were used as dispersed particles for a study of electrorheological (ER) suspensions. The characterization of each ER fluid as a function of controlled molecular structure in suspension showed different ER behaviors. In particular, the suspension of the S/HSDR gradient copolymer showed the greatest degree of enhancement in shear viscosity, by as much as a factor of 10, upon application of a 1700 kV/m electric field.