Surface-initiated organocatalyzed atom transfer radical polymerization (SI O-ATRP) provides a greener alternative to conventional ATRP by substituting organic dyes for copper salts. Consequently, this method yields polymer brushes free from metal contaminants, which are highly desirable in semiconductor and medical sectors. The organic dyes used in SI O-ATRP are photoactivated, which further allows for facile generation of surface patterns, complex polymer brush architectures, and molecular weight gradients. However, research on SI O-ATRP has focused mainly on small substrates (&lt;1 cm<sup>2</sup>), and brush films on larger substrates are limited to thicknesses &lt;50 nm, possibly resulting from an early termination. Despite a whole catalogue of advanced dyes for O-ATRP in solution, only one has been tested in SI O-ATRP. We show that a dye with appropriate photophysical properties is advantageous also for SI O-ATRP. In the course of our experiments, we identified side reactions that contribute to early termination. Carefully adapting the reaction parameters allowed us to expand the available range of dry film thickness to &gt;200 nm on a 20 cm<sup>2</sup> silicon wafer. Furthermore, we were able to grow hydrophilic, hydrophobic, as well as diblock copolymer brushes with excellent spatio-temporal control using a very small (ppm) amount of a photocatalyst. Notably, in addition to reducing the catalyst amount by 20-fold, we were able to double the accessible dry film thickness compared to previous reports on similar substrates. Linear polymerization growth profiles and up to three reinitiation cycles from the same substrate reveal the controlled nature of SI O-ATRP under the investigated reaction parameters. We are convinced that our findings and the simplicity of this technique will widen the interest of the polymer brush community in SI O-ATRP.

Shining light on surface-initiated organocatalyzed atom transfer radical polymerization

ACS Spring 2022

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