Synthesis of High Molecular Weight Polymethacrylates with Polyhedral Oligomeric Silsesquioxane Moieties by Atom Transfer Radical Polymerization

A new polyhedral oligomeric silsesquioxane (POSS) methacrylate monomer, 1-(3-(methacryloyloxy)-propyl)dimethylsiloxy-3,5,7,9,11,13,15-hepta(isobuty1)- pentacyclo- [9.5.1.1(3,9).1(5,15).1(7'13)] octasiloxane ( (i-Bu)(7)POSS-OSiMe2-MA, 1), with a flexible spacer between the cubic POSS cage and methacrylate group was synthesized to reduce steric strain and thus achieve polymethacrylates (poly(POSS-MA)s) with high molecular weight (MW). Atom transfer radical polymerization (ATRP) of 1 at high monomer concentration (1 M, corresponding to ca. 85 wt % of 1) led to polymers with the absolute number-average MW, determined by multiangle laser light scattering, M-n,M-MALLS = 2 350 000 (and apparent MW, measured by gel permeation chromatography with linear poly(methyl methacrylate) (PM.MA) standards, M-n,M-GPC = 550 000). Optimization of the reaction conditions, induding the ATRP catalyst, targeted degrees of polymerization, monomer concentrations, as well as a monomer feeding, resulting in the first well-defined high MW polymers with POSS moieties.