Synthesis and characterization of bead-like poly(N-isopropylacrylamide) copolymers with double decker silsesquioxane in the main chains

Abstract

Bead-like PNIPAAm copolymers with double-decker silsesquioxane (DDSQ) in the main chains were synthesized via a reversible addition–fragmentation chain transfer (RAFT) polymerization approach. The macromolecular chain transfer agent used for the RAFT polymerization was synthesized via the polycondensation of 3,13-dihydroxyproplyl DDSQ with S,S′-bis(α,α′-dimethyl-α′′-propargyl acetate)trithiocarbonate. The organic–inorganic copolymers with variable contents of DDSQ were characterized by means of ¹H nuclear magnetic resonance spectroscopy and gel permeation chromatography. Transmission electron microscopy showed that the bead-like PNIPAAm copolymers were microphase-separated in bulk. It was found that the glass transition temperatures (T_g's) of PNIPAAm microdomains of the organic–inorganic copolymers were lower than plain PNIPAAm and decreased with increasing the content of DDSQ. The bead-like PNIPAAm copolymers displayed the self-assembly behavior in aqueous solutions. Depending on the content of DDSQ, the bead-like organic–inorganic copolymers can self-assemble into spherical or vesicular nanoobjects in aqueous solutions. Both micro-differential scanning calorimetry (Micro-DSC) and cloud point analysis with UV-vis spectroscopy showed that the lower critical solution temperature (LCST) behavior of PNIPAAm subchains in the bead-like copolymers was significantly affected by the POSS cages in the main chains.