Nitroxide-mediated radical polymerization of methacryloisobutyl POSS and its block copolymers with poly(n-acryloylmorpholine)

Nitroxide-mediated radical polymerization (NMP) of the bulky methacryloisobutyl-polyhedral oligomeric silsesquioxane (POSS-MA) is successfully achieved after optimizing reaction conditions such as selection of controlling comonomer, comonomer feed molar ratio, and temperature (10 mol % styrene (S) comonomer at 110 °C using the commercially available BlocBuilder as the NMP initiator). The P(POSS-MA-co-S) with a molecular weight of ~8000 g/mol and dispersity Ж1.2 is afforded under the optimized reaction conditions. The chain-end fidelity is verified by chain extension experiments with N-acryloyl morpholine (ACM) via NMP that produces well-defined amphiphilic hybrid P(POSS-MA-co-S)-b-P(ACM)_x block copolymers, where the subscript “x” represents the degree of polymerization of (ACM) block (182 < x < 695). The size exclusion chromatography (SEC) of the as-synthesized samples reveals the presence of some dead P(POSS-MA-co-S) chains that could be removed by a simple purification step. Kinetic investigations reveal a first-order kinetics for the polymerization of ACM using P(POSS-MA-co-S) as the macroinitiator under NMP conditions. The kinetic and SEC data confirms the controlled nature of the NMP of ACM. Being amphiphilic, the formed P(POSS-MA-co-S)-b-P(ACM)_x block copolymers self-assembled in aqueous solution as revealed by the fluorescence spectroscopy experiments with pyrene as the probe for determination of the critical micelle concentration and dynamic light scattering studies.