Thicker is Better? Synthesis and Evaluation of Well‐Defined Polymer Brushes with Controllable Catalytic Loadings

Abstract

Polymer brushes (PBs) have been used as supports for the immobilization of palladium complexes on silicon surfaces. The polymers were grown by surface-initiated atom-transfer radical polymerization (SI-ATRP) and postdecorated with dipyridylamine (dpa) ligands. The pendant dpa units were in turn complexed with [Pd(OAc)(2)] to afford hybrid catalytic surfaces. A series of catalytic samples of various thicknesses (ca. 20-160 nm) and associated palladium loadings (ca. 10-45 nmol cm(-2)) were obtained by adjusting the SI-ATRP reaction time and characterized by ellipsometry, X-ray reflectivity, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS revealed a near-linear relationship between thickness of the polymer brush and palladium content, which confirmed the robustness of the preparation and postmodification sequence presented herein, rendering possible the creation of functional architectures with predefined catalytic potential. The activities of the catalytic PBs were determined by systematically exploring a full range of substrate-to-catalyst ratios in a model palladium(0)-catalyzed reaction. Quantitative transformations were observed for loadings down to 0.03 mol % and a maximum turnover number (TON) of around 3500 was established for the system. Comparison of the catalytic performances evidenced a singular influence of the thickness on conversions and TONs. The limited recyclability of the hairy catalysts has been attributed to palladium leaching.

Effects of Thickness and Grafting Density on the Activity of Polymer‐Brush‐Immobilized Tris(triazolyl) Copper(I) Catalysts

“…PHEMA brushes were grown on freshly activated Si chips and functionalized using a method described previously (Scheme ) 9h. 26 Briefly, the stepwise synthetic procedure started with the coating of single‐crystal Si wafers (1×1 cm 2 ) with an initiator monolayer.…”

“…Remarkably, it is possible to fine‐tune the properties of these thin polymer films by adjusting their composition and thickness. For instance, the catalytic content of the film can be controlled by modifying the thickness of the pristine precursor brush 9h. Recently, Verboom and co‐workers demonstrated that random copolymer brushes that consist of mixed active and cooperative segments significantly improved the performance of the corresponding catalytic homopolymer brushes 9l.…”

“…In continuation of our efforts to develop ultrathin films for application in catalysis,9h, 25 we report here the use of poly(2‐hydroxyethyl methacrylate) (PHEMA) polymer brushes for the immobilization of tris[(1,2,3‐triazolyl)methyl]amine (TTMA) CuCl catalysts and their investigation in a model CuAAC reaction with a particular focus on the effects of brush thickness and grafting density (Scheme ).…”

Piperazine-Containing Polymer Brush Layer as Supported Base Catalyst in a Glass Microreactor

“…Polymer brushes represent a robust platform that offers a myriad of possibilities to perform supported catalysis [13,14]. Using polymer brushes as a supporting material, we have reported the successful immobilization of catalysts, namely, a basic organocatalyst [15], metallic nanoparticles [16], enzymatic catalysts [17], and a Lewis acid [18], to the interior of the microchannel walls of a glass microreactor.…”

Gallium-containing polymer brush film as efficient supported Lewis acid catalyst in a glass microreactor

“…Polymer brushes have proven to provide a unique platform in supported catalysis [14–15]. Previously, we have described the successful immobilization and evaluation of catalysts (e.g., basic organocatalyst [6], metallic nanoparticles [16], and enzymatic catalyst [17]) to the microchannel walls using polymer brushes.…”