Preparation of shell cross-linked thermoresponsive micelles as well as hollow spheres based on P(NIPAAm-co-HMAAm-co-MPMA)-b-PCL

A novel amphiphilic block copolymer poly(N-isopropylacrylamide-co-N-hydroxymethylacrylamide-co-3-(trimethoxysilyl)propyl methacrylate)-b-poly(epsilon-caprolactone) (P(NIPAAm-co-HMAAm-co-MPMA)-b-PCL) bearing thermosensitivity as well as biodegradability was synthesized for the production of hollow spheres. A three-step approach was employed to prepare shell cross-linked (SCL), thermoresponsive hybrid hollow spheres: (1) micellization of P(NIPAAm-co-HMAAm-co-MPMA)-b-PCL, (2) cross-linking of the hydrophilic shell via acid-catalyzed sol-gel process, and then (3) degrading the PCL core with an enzyme. Transmission electron microscopy (TEM) studies and size measurements showed that the resultant hollow spheres exhibited regularly globular shape with diameter of around 170 nm. The structures of the SCL micelles and the hollow spheres were characterized by Fourier-transform infrared (FT-IR) measurements and laser light scattering (LLS) analyses. The SCL hollow spheres showed reversible dispersion/aggregation in response to temperature cycles through lower critical solution temperature (LCST) of the outer cross-linked shell at around 37 degrees C. The SCL micelles as well as hollow spheres prepared here may be used as nanocarriers for catalytic particles, molecules with electronic and photonic functions, as well as biological and medical species.