Candidate materials for low-loss optical waveguides based on poly(glycidyl methacrylate-ran-pentafluostyrene) [P(GMA-ran-PFS)] copolymers were synthesized by nitroxide mediated polymerization (NMP) initiated with BlocBuilder (R) [N-(2-methylpropyl)-N-(1-diethlphosphono-2,2-dimethylpropyl)-O-(2-carboxylprop-2-yl) hydroxylamine] bearing a succinimidyl ester group (NHS-BlocBuilder) at 90 degrees C in 1,4 dioxane. The copolymerizations yielded copolymers with low dispersity Mw/Mn between 1.2 and 1.4. The core structure of single-mode channel waveguides was fabricated by direct UV lithographic patterning. The copolymers with low Mw/Mn resulted in line width roughness (LWR) of about 0.16 m, whereas LWR of copolymers with Mw/Mn=3.5 but similar compositions was about 0.5 m. The improvement in microstructural control allotted by NMP permitted finer pattern replication for copolymers desired for optical waveguides, as suggested for photoresist polymers. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2970-2978