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

Xue, L Agarwal, US Zhang, M Staal, BBP Muller, AHE Bailly, Christian [UCL] Lemstra, PJ

We report synthesis and direct topology visualization of single molecules of six-arm star poly(methyl 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-bromo2-methylpropionate)] benzoylate (linear-core initiator). Their structures differ in the linking arrangement of the initiating sites. Atom transfer radical polymerizations (ATRP) of methyl methacrylate (MMA) from these initiators using CuCl as the catalyst and 4,4'-di-n-nonyl-2,2'-bipyridine as the ligand at 90 degrees C produced six-arm star PMMAs with very high molecular weight ((M) over bar (w) > 2 million) and narrow molecular weight distribution (polydispersity index approximate to 1.3). A high initiation efficiency (> 90%) of the initiating sites is inferred from a good match of the (M) over bar (w) of the star PMMA with the expected value based on (M) over bar (w) of the cleaved arms. SEC-LS analysis 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 resolution of the individual arms linked to the initiating core and allowed clear identification of predominantly six-arm star molecules.