Preparation of monodispersed PNIPAm/silica composites and characterization of their thermal behaviors

Two types of thermosensitive poly(N-isopropylacrylamide) (PNIPAm)-silica organic/inorganic hybrid particles were successfully prepared in aqueous solution through a facile synthetic process. Silane coupler of vinyl organic groups connects the PNIPAm to silica. First, hybrid spheres were prepared by grafting PNIPAm polymers to VTMS (vinyl trimethoxysilane) silica spheres. The thickness of polymer shell on the silica surfaces could be easily controlled by varying the concentrations of NIPAm monomer. Second, another type of hybrid particle was fabricated by encapsulating PNIPAm polymer with silica materials. The PNIPAm polymers were completely encapsulated by silica shell. The morphologies and shell thickness were characterized through SEM and TEM. The variations of phase transition temperature of PNIPAm were measured using DSC.