Swelling properties of amino acid containing cross-linked polymeric organogels and their respective polyelectrolytic hydrogels with pH and salt responsive property

Abstract

Amino acid based superabsorbent polymer (SAP) organogel library has been synthesized from Boc-glycine/alanine/valine/leucine/isoleucine/phenylalanine methacryloyl-oxyethyl ester (Boc-Gly/Ala/Val/Leu/Ilu/Phe-HEMA), which can switch over to corresponding hydrogels by simple one step Boc deprotection method. Swelling behaviour of organogels is investigated in various organic solvents (dielectric constant (ε) between 2.25 and 46.7), shows superabsorbent property in nonpolar organic solvents (2.25 ≤ ε ≤ 10.26) and moderate degree of swelling in polar aprotic solvents like acetone, N,N-dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), etc. Swelling property of organogels is greatly influenced by the –R group of pendant amino acids and increases as bulkiness and hydrophobicity of –R increased. Organogels release absorbed volatile organic compounds (VOCs) very rapidly at room temperature and bulkiness of –R group accelerate the deswelling kinetic. Deprotection of Boc groups in the organogel network converts them to superabsorbent cationic polyelectrolyte hydrogels with high degree of swelling (∼518 for hydrogel from leucine) due to the presence of –NH3+ ion functionality, and the swelling ratio of hydrogels is drastically affected by the –R group of amino acids moiety, pH of aqueous medium and ionic strength of the solutions.