Synthesis and characterization of heptaphenyl polyhedral oligomeric silsesquioxane-capped poly(N-isopropylacrylamide)s

In this work, a novel initiator bearing heptaphenyl polyhedral oligomeric silsesquioxane (POSS) was synthesized via the copper-catalyzed Huisgen 1,3-cycloaddition (i.e., click chemistry). With this initiator, the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) was carried out to afford the POSS-capped PNIPAAm. The organic-inorganic amphiphiles were characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). Atomic force microscopy (AFM) showed that the POSS-capped PNIPAAm amphiphiles in bulk displayed microphase-separated morphologies. In aqueous solutions, the POSS-capped PNIPAAm amphiphiles were self-assembled into micelle-like aggregates as evidenced by dynamic light scattering (DLS) and transmission election microscopy (TEM). It was found that the sizes of the self-organized nanoobjects decreased with increasing the lengths of PNIPAAm chains. By means of UV-vis spectroscopy, the lower critical solution temperature (LCST) behavior of the organic-inorganic amphiphiles in aqueous solution was investigated and the LCSTs of the organic-inorganic amphiphiles decreased with increasing the percentage of POSS termini. It is noted that the self-assembly behavior of the POSS-capped PNIPAAm in aqueous solutions exerted the significant restriction on the macromolecular conformation alteration of PNIPAAm chains while the coil-to-globule collapse occurred. (C) 2012 Elsevier Ltd. All rights reserved.