Polyacrylamide and poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid)-silica composite nanogels through in situ microemulsion polymerisation

Nanosize monodisperse composite particles of polyacrylamide (PAM) and poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid)-silica [Poly(AM-co-AMPSA)-SiO2] were prepared by water-in-oil in situ microemulsion polymerisation without surface treatment of silica. The synthesised composite particles were produced with controllable sizes ranging from 44 to 77 nm in diameter. Presence of silica filler in the nanoreactors facilitates the formation of well-defined discrete particles. The prepared nanocomposites were characterised by dynamic light scattering, transmission electron microscope, Fourier transform infrared spectrophotometer, thermogravimetric analyzer, differential scanning calorimeter, scanning electron microscope and X-ray diffraction. The spectroscopic result shows strong interactions of silica nanoparticles with sulphonic groups of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA). The onset degradation temperature is increased from 227 to 262 °C in copolymer–silica composite as compared to polyacrylamide–silica (PAM–SiO2) which indicates improved thermal stability. The shifting of glass transition temperature from 194 to 203 °C in copolymeric composite nanogels further confirms the existence of strong interactions of silica filler with poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid) [Poly(AM-co-AMPSA)] chains. Also the chemical composition of polymeric chains and the affinity of polymer chains and silica influenced the morphology of nanogels.