Temperature and pH dual-responsive behavior of polyhedral oligomeric silsesquioxane-based star-block copolymer with poly(acrylic acid-block-N-isopropylacrylamide) as arms

摘要

Poly(acrylic acid-block-N-isopropylacrylamide) (PAAc-b-PNIPAm)-tethered octafunctional polyhedral oligomeric silsesquioxane (POSS) were synthesized via POSS-initialized atom transfer radical polymerization. When very short PAAc blocks are placed between the POSS core and PNIPAm short chains, the critical temperature (T _c) of POSS-PAAc-b-PNIPAm determined by cloud point measurements varies in a wide temperature range with pH, and its T _c is even lower than that of POSS-PNIPAm with similar chain length at pH = 5.0, indicating a synergic effect between high local chain density and intramolecular interaction between PAAc and PNIPAm. When the PAAc blocks are relatively long, the pH response of POSS-PAAc-b-PNIPAm diminishes owing to the reduced local PNIPAm chain density.