Polymethylene Brushes via Surface-Initiated C1 Polyhomologation.

Surface-initiated polymerization reactions are a powerful tool to generate chain-end-tethered polymer brushes. This report presents a synthetic strategy that gives access to structurally well-defined hydrocarbon polymer brushes of controlled molecular weights, which can be further modified to generate more complex surface-attached polymer architectures. The hydrocarbon brushes reported in this study are polymethylene brushes that are obtained via surface-initiated C1 polyhomologation of dimethylsulfoxonium methylide. The strategy outlined here is based on the use of an alkylboronic acid pinacol ester initiator, which allows for controlled, unidirectional chain growth by monomer insertion into only the C-B bond of the initiator and which presents the polymerization active group at the growing polymer chain end. This surface-initiated C1 polyhomologation methodology is compatible with photopatterning strategies and can be used to generate micropatterned polymethylene brush films. Furthermore, conversion of the boronic ester chain-end functionalities to hydroxyl groups allows for selective chain-end modification and enables access to a variety of surface-anchored block copolymer architectures by chain extension via, for example, ring-opening or atom transfer radical polymerization chemistries.

Tuning the Thermoresponsive Behavior of Surface-Attached PNIPAM Networks: Varying the Crosslinker Content in SI-ATRP.

The synthesis and thermoresponsive properties of surface-attached poly(N-isopropylacrylamide)-co-N,N'-methylene bisacrylamide (PNIPAM-co-MBAM) networks are investigated. The networks are formed via SI-ARGET-ATRP ("grafting-from") on thiol-based initiator-functionalized gold films. This method is reliable, well controlled, fast, and applicable to patterned surfaces (e.g., nanopores) for networks with dry thicknesses >20 nm. Surface-attached PNIPAM-co-MBAM gels are swollen below their volume phase transition temperature but above collapse without complete expulsion of water (retain ∼50 vol %). The swelling/collapse transition is studied using complementary SPR and QCMD techniques. The ratio between swollen and collapsed heights characterizes the thermoresponsive behavior and is shown to not depend on network height but to vary with MBAM content. The higher the proportion of the crosslinker, the lower the magnitude of the phase transition, until all responsiveness is lost at 5 mol % MBAM. The temperature range of the transition is broadened for more crosslinked PNIPAM-co-MBAM gels but remains centered around 32 °C. Upon reswelling, less crosslinked networks display sharp transitions, while for those containing ≥3 mol % MBAM, transitions remain broad. This tunable behavior persists for gels on nanostructured gold surfaces. Investigating PNIPAM-co-MBAM networks on gold plasmonic nanowell arrays is a starting point for expanding their scope as thermo-controlled nanoactuators.

Hydrothermal Generation of Conjugated Polymers Using the Example of Pyrrone Polymers and Polybenzimidazoles.

Various polyimides and polyamides have recently been prepared via hydrothermal synthesis in nothing but H2 O under high-pressure and high-temperature conditions. However, none of the prepared polymers feature a truly conjugated polymer backbone. Here, we report on an expansion of the synthetic scope of this straightforward and inherently environmentally friendly polymerization technique to the generation of conjugated polymers. Selected representatives of two different polymer classes, pyrrone polymers and polybenzimidazoles, were generated hydrothermally. We present a mechanistic discussion of the polymer formation process as well as an electrochemical characterization of the most promising product.