Characterization of NIPA for pH Sensing and Metal Ion Binding

Abstract

A methodology to characterize acrylamide polymers that respond to environmental stimuli (e.g., temperature and pH) was developed. Copolymers of N-isopropylacrylamide were synthesized at ambient temperature by dispersion polymerization. The polymer microspheres were then cast into a hydrogel membrane, and turbidity was measured by placing the membrane in a special Teflon holder, which could be mounted in a conventional cuvet that contained the sample solution. The pH induced volume phase transition was investigated as a function of temperature, percent crosslinking, amount and nature of comonomer used in the formulation, ionic strength of the sample solution, and particle size. Metal ion binding with NIPA based polymer particles was also investigated. For alkali earth metals, an ion exchange mechanism is proposed whereas for transition metal ions, binding is accompanied by the formation of a chelate between the metal ion and the carboxylic acid group of the functional comonomer and the amide of NIPA.