Swelling Behavior of Poly(N-isopropylacrylamide) Nanogels with Narrow Size Distribution Made by Semi-continuous Inverse Heterophase Polymerization

Abstract

The synthesis of poly(N-isopropylacrylamide) nanogels by semi-continuous inverse heterophase polymerization (SIHP) under monomer starved conditions is reported here. This process consists in adding a N-isopropylacrylamide (NIPA) aqueous solution at a controlled rate over a monomer-free oleic solution containing surfactant and initiator. The nanogels became smaller with narrower size distributions as the addition rate was decreased. Moreover, nanogel sizes, the size distributions and more importantly, the polymer/surfactant ratios were smaller than those of PNIPA nanogels synthesized by batch inverse microemulsion polymerization (BIMP). The swelling behavior of these nanogels in water as a function of temperature is reported. As expected, all nanogels have a volume phase transition temperature at ca. 33–34°C.

Keywords:

• Poly(N-isopropylacrylamide) nanogels
• semi-continuous inverse heterophase polymerization
• batch inverse microemulsion polymerization