Co-polymer microgels : contemporary physico-chemical, structural and analytical investigations
Poly(N-isopropylacrylamide), [poly(NIPAM)], is a thermosensitive polymer which undergoes a conformational transition at approximately 32°C in aqueous solution. NIPAM is a monomer commonly employed in microgel synthesis and the resultant particles are thermosensitive, a property which can be altered by modification of the system by co-polymerisation. A series of colloidal microgels have been prepared by surfactant-free emulsion polymerisation (SFEP) based on the NIPAM monomer. Butyl acrylate (BuAc) has been used as a co-monomer in order to alter the physico-chemical properties of poly(NIPAM) microgel particles. Thermosensitive poly(NIPAM/BuAc) homopolymeric/co-polymers microgels have been prepared with various monomer ratios, ranging from pure poly(NIPAM) to pure poly(BuAc), both cross-linked using N', N'-methylenebisacrylamide (BA). The microgel series have been characterised by turbidimetric analysis, dynamic light scattering, electrophoretic mobility measurements and TEM to determine particle size and volume phase transition (VPT) behaviour. The incorporation of BuAc has been found to reduce the volume phase transition temperature (VPPT) of poly(NIPAM). Small-angle neutron scattering (SANS) has been employed as a structural probe to interrogate the internal particle structure of co-polymer microgel particles prepared in a one pot reaction. The structure, with respect to monomer distribution, has been investigated by contrast matching SANS, using both deuteriated and non-deuteriated microgel particles. Co-polymer microgels prepared using NIPAM and BuAc, synthesised by SFEP in a one-pot reaction, were found to possess a structure comprising of regions rich in BuAc appearing as defined clusters within the gel like network.