Polystyrene latex particles coated with crosslinked poly(N-isopropylacrylamide).
Thermoresponsive colloidal particles were prepared by seeded precipitation polymerization ofN-isopropylacrylamide (NIPAM) in the presence of a crosslinking monomer,N,N-methylenebisacrylamide (MBA), using polystyrene latex particles (ca. 50 nm in diameter) as seeds in aqueous dispersion. Phase transitions of the prepared poly(N-isopropylacrylamide), PNIPAM, shells on polystyrene cores were studied in comparison to colloidal PNIPAM microgel particles, in H2O and/or in D2O by dynamic light scattering, microcalorimetry and by1H NMR spectroscopy including the measurements of spin-lattice (T1) and spin-spin (T2) relaxation times for the protons of PNIPAM. As expected, the seed particles grew in hydrodynamic size during the crosslinking polymerization of NIPAM, and a larger NIPAM to seed mass ratio in the polymerization batch led to a larger increase of particle size indicating a product coated with a thicker PNIPAM shell. Broader microcalorimetric endotherms of dehydration were observed for crosslinked PNIPAM on the solid cores compared to the PNIPAM microgels and also an increase of the transition temperature was observed. The calorimetric results were complemented by the NMR spectroscopy data of the1H-signal intensities upon heating in D2O, showing that the phase transition of crosslinked PNIPAM on polystyrene core shifts towards higher temperatures when compared to the microgels, and also that the temperature range of the transition is broader.
Laboratory of Polymer Chemistry, Department of Chemistry, University of Helsinki, PB 55, Helsinki, 00014 Finland.
Mirja
M
Andersson
Sami
S
Hietala
Heikki
H
Tenhu
Sirkka Liisa
SL
Maunu
1H NMR; Core-shell; Microcalorimetry; Microgel; Poly(N-isopropylacrylamide)