Synthesis and characterization of poly (N-isopropylacrylamide-copolymerised-acrylic acid) poly(NIPAM-co-AAc) nanogel / Nurul Ain Norkavi

Poly(N-isopropylacrylamide)(polyNIPAM) is one of the most well known smart polymers with thermoresponsive behaviour. The cross-linked poly NIP AM exhibits a conformational transition in the form of volume collapse in the range of 32 - 34 °C in an aqueous solution, below which the polymer particles are hydrophilic and above which they become hydrophobic. From the point of view of potential applications, the polymer would be useful as a drug carrier if they could respond to multiple stimuli simultaneously. In the work described here, a hydrophilic monomer, acrylic acid (AAc), was copolymerised into the polyNIPAM to obtain poly(NIPAM-co­ AAc), a polymer that is responsive to both, external pH and temperature stimuli. The particle size, thermal and pH-responsive properties, zeta potential, heat capacity of the particles in an aqueous solution and morphology were investigated. The results suggested that the synthesized poly(NIPAM-co-AAc) by the surfactant-free emulsion polymerisation (SFEP) technique produced particles of micron scale (25 µm). Additionally, the particles were not significantly sensitive to temperature and pH stimuli. Its lower critical solution temperature was found to be 30°C, which is lower than the control (polyNIPAM). In conclusion, the SFEP technique and the purification method acquired have to be optimised in order to obtain multi-sensitive polymer particles of submicron size.