Synthesis and direct topology visualization of high-molecular-weight star PMMA

We report synthesis and direct topol. visualization of single mols. of six-arm star poly(Me methacrylate) (PMMA). We synthesized two hexafunctional initiators, 2,3,6,7,10,11-triphenylene hexa-2-bromo-2-methylpropionate (fused-core initiator) and ethylene glycol bis[3,4,5-tri(2-bromo-2-methylpropionate)] benzoylate (linear-core initiator). Their structures differ in the linking arrangement of the initiating sites. Atom transfer radical polymns. (ATRP) of Me methacrylate (MMA) from these initiators using CuCl as the catalyst and 4,4'-di-n-nonyl-2,2'-bipyridine as the ligand at 90 DegC produced six-arm star PMMAs with very high mol. wt. (.hivin.Mw> 2 million) and narrow mol. wt. distribution (polydispersity index ~ 1.3). A high initiation efficiency (>90%) of the initiating sites is inferred from a good match of the .hivin.Mw of the star PMMA with the expected value based on .hivin.Mw of the cleaved arms. SEC-LS anal. confirmed the compact structure of the star PMMA compared to linear PMMA and the absence of star-star coupling. Tapping mode scanning force microscopy of a dip-coated sample on mica enabled resoln. of the individual arms linked to the initiating core and allowed clear identification of predominantly six-arm star mols