Modification of Thermoresponsive Poly(<i>N</i>-Isopropylacrylamide) End-Group with Hydrophilic and/or Hydrophobic Compounds Tuned the LCST

Abstract

Poly (N-isopropylacrylamide) (PNIPAAm) is one of the most well-known thermoresponsive polymers that exhibits a reversible coil-to-globule transition in aqueous solution at lower critical solution temperature (LCST) (32°C). PNIPAAm behave as an extended coil form in an aqueous solution below the LCST, meanwhile, above the LCST, it shrinks into a globule form. The LCST of PNIPAAm could be tune when it is chemically modified with hydrophilic and/or hydrophobic compound. In this study, modifications of PNIPAAm end-group with maleimide or phenyl maleimide compounds were prepared and their LCST behaviours were investigated. One end-group of synthesized poly (N-isopropylacrylamide)-chain transfer agent (PNIPAAm-CTA) was modified with maleimide or phenyl maleimide compound through aminolysis reaction to form PNIPAAm-Maleimide (PNIPAAm-M) and PNIPAAm-Phenyl maleimide (PNIPAAm-PhM). Maleimide is a hydrophilic compound, and phenyl maleimide is a slight hydrophobic compound were used in this study. The modification with hydrophilic compound will higher the LCST of PNIPAAm. The slight hydrophobic of phenyl maleimide compound will decrease the LCST. In this study, the successfulness of aminolysis process of PNIPAAm-CTA were determined through the fourier transform infrared (FTIR). Moreover, the LCST behavior of PNIPAAm-CTA, PNIPAAm-M and PNIPAAm-PhM were determined through light scattering intensity analysis. The results indicated that upon heating the solutions of PNIPAAm-CTA, PNIPAAm-M and PNIPAAm-PhM in 10 mM HEPES solution pH 7.4 at 25°C–40°C, PNIPAAm-CTA, and PNIPAAm-PhM solutions started to increase their light intensities at 35°C and PNIPAAm-M at 36°C, respectively. To conclude, modification of PNIPAAm end-group with hydrophobic and/or hydrophilic compound could tune their LCST.