Dual thermo- and pH-sensitive poly(2-hydroxyethyl methacrylate-co-acrylic acid)-grafted graphene oxide
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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 °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.
KeywordsGraphene oxide Poly(2-hydroxyethyl methacrylate) Poly(acrylic acid) Block copolymer Stimuli responsive
We are grateful for support from the Iran National Science Foundation (INSF) (grant no. 91002479).
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