The effect of pH on the LCST of poly(N-isopropylacrylamide) and poly(N-isopropylacrylamide-co-acrylic acid)

Abstract

Poly(N-isopropylacrylamide) (PNIPAAm) and poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAAm-co-AAc)) hydrogels are synthesized by irradiating the aqueous solutions of NIPAAm and NIPAAm/AAc with 60Co gamma-ray. The effects of pH on the swelling ratio and on the lower critical solution temperature (LCST) are studied by determining the dependence of swelling ratio on temperature in different pH butter solutions. Differential scanning calorimetry (DSC) is applied in determination of the LCST of the hydrogels. Fourier transform infrared (FT-IR) spectrometry is used in the comparison of hydrogels swelled in various pH conditions. As a result, PNIPAAm was found to be a pH-sensitive hydrogel and the LCST of the PNIPAAm and P(NIPAAm-co-AAc) hydrogels are influenced by pH.

Biopolymer-based Stimuli-Responsive Polymeric Systems for Functional Finishing of Textiles

“…It shows that particle size is very sensitive to pH change as a result of protonation/deprotonation of chitosan. At pH 3 the hydrodynamic diameter is noticeably smaller compared to the values obtained at other pH values, which can be explained by previously reported (Pei et al, 2004) significant pH-dependence of poly-NiPAAm LCST value (it decreases!) in strong acidic medium.…”

Thermoresponsive hydrogels in biomedical applications

“…Recent developments on pNiPAAm-based hydrogels include their use for drug delivery [12,13,37,38], cell encapsulation and delivery [39,40] and cell culture surfaces [41]. Poly(Nisopropylacrylamide) is non-biodegradable and exhibits a sharp phase transition, with an LCST at about 32°C in pure water [37,42]. Below the LCST, pNiPAAm assumes a flexible, extended coil conformation in aqueous solutions.…”

“…Likewise, copolymerization with a more hydrophobic monomer results in a lower LCST than pNiPAAm [44]. Moreover, the phase transition temperature is influenced by the presence of salts [45] and pH to a certain extent [42,45].…”

DNA Hybridization in Thermoresponsive Polymer Nanoparticles

“…The polymer becomes hydrophobic and collapses to a globular conformation. [1,3,5,7,8] We have prepared core-shell polymer nanoparticles with a glassy poly(methyl methacrylate) (PMMA) core and a crosslinked thermoresponsive shell of PNIPAM and aminoethyl methacrylate hydrochloride (AEMH). [9] The positively charged co-monomer is used to increase the absorption of the negatively charged DNA strands.…”