Stereoregular Methacrylate-POSS Hybrid Polymers: Syntheses and Nanostructured Assemblies

This contribution reports the first examples of stereoregular (isotactic, it -, and syndiotactic, st -) methacrylate-POSS (polyhedral oligomeric silsesquioxane) hybrid polymers and their derived nanostructured assemblies. The polymerization of methyl methacrylate (MMA) by isospecific and syndiospecific living metallocene catalysts, when end-capped with methacrylisobutyl POSS (MA-POSS) or simultaneously copolymerized with MA-POSS at ambient temperature, readily produces highly stereoregular (94% it - and st -) MA-POSS end-capped PMMA (PMMA-POSS) or statistical copolymers PMMA- co -P(MA-POSS). The MA-POSS incorporation in the it -copolymers ranges from a low 2.6 mol % (20 wt %) to a high, maximum 24 mol % (75 wt %), whereas the incorporation in the st -copolymers is relatively lower with the same comonomer feed ratio due to the formation of a crystalline inclusion complex in which the POSS nanocages are encapsulated within the helical st -PMMA cavity. The it -copolymers with high POSS contents (>20 mol %) show evidence for interchain association through POSS aggregation and display a ∼20 °C T g enhancement over the pristine it -PMMA. MA-POSS end-capped diastereomeric PMMAs exhibit versatile nanostructured assemblies, including micelle-like core−shell nanostructures ( R h up to 186 nm derived from the 5.7 nm it -PMMA-POSS unimer) through POSS inorganic collapse in selective solvents, helical stereocomplexes ( R h = 11 nm) between two or three polymer chains through organic self-organization of the diastereomeric PMMAs, and large core−shell nanospheres ( R h up to 636 nm) through synergistic organic PMMA self-organization and inorganic POSS nanocluster aggregation. Thermal annealing of the it -/ st -PMMA-POSS blend in a 1:2 ratio also generates the crystalline stereocomplex with a high T m of 213 °C.