THE INFLUENCE OF COMPOSITION ON THE PROPERTIES OF PH-SWELLABLE POLYMERS FOR CHEMICAL SENSORS

Aminated polystyrene swells at low pH due to electrostatic repulsion b etween charged sites on the polymer. The effects of polymer formulatio n on the rate and degree of swelling and on the penetration modulus ha ve been evaluated for porous aminated polystyrene beads prepared by su spension polymerization. The following parameters were varied in a 3x3 x3x2 factorial experiment: 1) percent crosslinking, 2) percent porogen ic solvent, 3) composition of porogenic solvent and 4) level of Kraton G1652, a styrene-ethylene, butylene-styrene triblock copolymer, added to toughen the polymer. The degree of swelling decreases at higher le vels of crosslinking. Swelling is greater when the polymer morphology is continuous rather than consisting of connected small spheres. The p ercentage of xylene in the porogenic solvent affects the degree of swe lling for underivatized beads in toluene but not for derivatized beads in acid. The rate of swelling of underivatized beads in toluene appea rs to involve toluene entering the pore space of the bead by capillary action. However, rates of swelling of derivatized bead in acid appear to be governed by the rate at which protons move through the bulk of the polymer rather than involving transport through pore space. The pe netration moduli are small for all beads and depend on the degree of c rosslinking, the amount of pore space in the bead and the polymer morp hology. (C) 1997 Elsevier Science S.A.