Tuning of lower critical solution temperature of thermoresponsive 2-hydroxy-3-alkoxypropyl hydroxyethyl cellulose by alkyl side chains and additives

Abstract

Two kinds of thermoresponsive 2-hydroxy-3-alkoxypropyl hydroxyethyl celluloses (HAPEC) were prepared by grafting butyl and isopropyl glycidyl ethers onto hydroxyethyl celluloses (HEC). The HAPEC was characterized by 1H NMR, 13C NMR, and 2D HSQC NMR. The lower critical solution temperature (LCST) of HAPEC can be tuned by changing the molar substitution (MS). The LCST decreased with the increasing MS of the alkyl chains. The HAPEC concentration, salt concentration, and organic solvent concentration had a marked influence on LCST. In addition, the differences of thermoresponsive properties between the two kinds of HAPECs were investigated. 2-Hydroxy-3-butoxypropyl hydroxyethyl cellulose (HBPEC), which has longer hydrophobic side chains, demonstrated a lower LCST when both HBPEC and 2-hydroxy-3-isopropoxypropyl hydroxyethyl cellulose (HIPEC) possessed similar MS values. HBPEC, which has longer hydrophobic side chains, exhibited thermoresponsive flocculation behavior, and the critical flocculation temperature (CFT) was adjusted in the range from 27.3 to 51.2 °C by changing the molar substitution.