Swellable Copolymers of N-isopropylacrylamide and Alkyl Acrylic Acids for Optical pH Sensing

Abstract

Swellable polymers that respond to pH (including a portion of the physiological pH range) have been prepared from N-isopropylacrylamide (NIPA) copolymerized with acrylic acid, methacrylic acid, ethacrylic acid or propacrylic acid by dispersion polymerization. When the swellable polymer particles are dispersed in a polyvinyl alcohol (PVA) hydrogel membrane, large changes occur in the turbidity of the membrane (which is measured using an absorbance spectrometer) as the pH of the buffer solution in contact with the hydrogel membrane is varied. The swelling of the NIPA copolymer is nonionic, as the ionic strength of the buffer solution in contact with the PVA membrane was increased from 0.1 to 1.0 M without a decrease in the swelling. For many of these NIPA copolymers, swelling was also reversible in both low- and high ionic strength pH-buffered media and at ambient and physiological temperatures. The composition of the formulation used to prepare these copolymers of NIPA can be correlated to the enthalpy and entropy of the pH-induced swelling.

Temperature‐Optimized Synthesis of SiO2‐Reinforced N‐(Alkyl)Acrylamide‐Based Semi‐IPN Hybrid Gels Functionalized with Methacrylic Acid Units

“…PNIPA copolymer with methacrylic acid showed reversible swelling both in 23 and 37 °C. [ 46 ] Zhang and Chu reported the effects of different polymerization temperature on the swelling/ deswelling kinetics and dynamic response of PNIPA gels prepared at 22, 0.5, and −20 °C in DMSO as the polymerization solvent. It was found that, in the shrinkage profiles of gels studied at 48 °C, the shrinkage rates of gels prepared at 0.5 and −20 °C are faster than those prepared at 22 °C.…”

Synthesis and Characterization of N-Isopropylacrylamide Microspheres as pH Sensors

“…Although a large number of studies have appeared in the literature on pH initiated swelling of acrylamide microgels [ 22 ], most of these studies have been limited to a specific pH-sensitive functional comonomer or a narrow temperature range. Only a few studies have been undertaken to delineate the effects of temperature and ionic strength on the pH response of a series of NIPA copolymers containing different pH-sensitive functional co-monomers [ 23 , 24 ]. However, the formulations used to synthesize these NIPA copolymers contained the same amount of pH-sensitive comonomer, NTBA, and crosslinker.…”