Dual thermo- and pH-sensitive poly(2-hydroxyethyl methacrylate-co-acrylic acid)-grafted graphene oxide

A two-step modification was used to attach atom transfer radical polymerization (ATRP) initiator onto graphene oxide surface. ATRP polymerization of 2-hydroxyethyl methacrylate (HEMA) was performed via "grafting from" approach. Due to uncontrolled ATRP of acrylic acid (AA), the Br-terminated P(HEMA) chains were converted to reversible addition-fragmentation chain transfer agent and polymerization of AA was done. The structure of modified nanosheets was characterized using X-ray diffraction analysis, Raman spectroscopy, proton nuclear magnetic resonance, scanning electron microscopy, and etc. These nanosheets showed dual pH- and thermo-sensitive properties as measured by UV-visible spectroscopy in different pH (2-13) and temperature (15-55 A degrees C) values. Generally, UV absorbance of P(HEMA-co-AA)-grafted nanosheets was higher than P(HEMA)-grafted nanosheets. Also, it seems that the poly(acrylic acid) block induces more pH sensitivity behavior than P(HEMA) block. Lower critical solution temperature of polymer-grafted nanosheets were shifted to higher temperature when chain extension was performed.