In-situ synthesis of thermosensitive microspheres by atom transfer radical polymerization

Monodispersed crosslinking polystyrene (PSt) microspheres with chlorine atoms on their surfaces were prepared by emulsifier-free emulsion copolymerization in acetone/water [V(acetone) : V(water) =4 : 6] mixed solvents with potassium persulfate as an initiator, divinylbenzene as a crosslinking agent and p-chloromethylstyrene (CMSt) as a functional monomer. Content of chlorine atoms on the surfaces of the crosslinked PSt microspheres was determined by X-ray photoelectron spectroscopy (XPS). Molar fraction of chlorine was 1.07% on the surfaces of the PSt microspheres based on the XPS analysis when n(CMSt) : n(St) was 5 to 95 in feed. N-Isopropylacrylamide (NIPAAm) was initiated through in-situ atom transfer radical polymerization (ATRP) using synthesized PSt microspheres as a macroinitiator and the grafted poly(N-isopropylacrylamide) chain was introduced onto the surfaces of the PSt microspheres. The properties of PNIPAAm-g-PSt microspheres, such as structure, morphology and diameter distribution were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy and laser light scattering (LLS) methods. It was shown that the PNIPAAm chains were grafted successfully on the surfaces of the crosslinked PSt microspheres, and its lower critical solution temperature was about 32 degrees C in water. The resulting PNIPAAm-g-PSt microspheres show the temperature sensitivity.