2011 Articles

Solid phase modular synthesis of polymacromer brushes and their isolation as molecular products by photocleavage from the substrate

Dach, Benjamin Isaac; Li, Xia; Turro, Nicholas J.; Koberstein, Jeffrey T.

We report a novel solid phase method for the sequential coupling of heterobifunctional macromonomers to form a new class of polymeric materials that we refer to as polymacromers. Starting from an azide functional substrate, α-azido, ώ-protected-alkyne macromonomers are added step-by step by thermally initiated click reactions. After each addition step, the terminal alkyne group is deprotected to allow addition of another macromonomer. The use of highly chemoselective click chemistry for the coupling reactions allows virtually any macromonomer to be employed, regardless of its chemical nature. The polymacromers may be left as polymer brushes on the substrate, or can be isolated as molecular products by photocleavage of an ortho-nitrobenzyloxycarbonyl (NBOC) linkage incorporated at the substrate interface. The method is illustrated by forming homopolymacromers by sequential coupling of poly(tert-butyl acrylate) macromonomers. The results of characterization of the polymacromer bushes by ellipsometry, contact angle analysis and x-ray photoelectron spectroscopy, and direct measurements of the molecular weights of isolated products by gel permeation chromatography demonstrate that polymacromers can be prepared with a coupling efficiency approaching 100%.