Thermally Induced Cross-Linking of Polymers via C,H Insertion Cross-Linking (CHic) under Mild Conditions

Abstract

The focus of studies performed so far on the formation of surface-attached polymer networks by C,H insertion cross-linking (CHic) reaction has been largely on photochemical activation. This study describes the thermal activation of the formation of (surface-attached) polymer networks under comparably mild conditions. A novel cross-linker, based on a diazo phenyl ester group, is incorporated into various copolymers, which are subsequently deposited on solid substrates. Upon activation, the cross-linker moieties generate carbene intermediates, which lead to rapid, complete cross-linking of the whole film and simultaneous surface attachment to various organic materials via CHic. Although this system requires only comparably mild conditions (i.e., below 100 °C) to become activated, a long shelf life at room temperature is observed. The presented system might be useful in a wide range of applications, from coatings to rather complex geometries. We demonstrate the covalent binding of protein-repellent thin films to the inner surface of (rubber) tubes and the generation of patterned structures by a “branding iron” approach. For this a hot structure is pressed onto a diazo polymer coated surface, leading in the contact zone to fast cross-linking while in all other areas the polymer remains soluble and is washed off during subsequent extraction.

Carbene-Mediated Polymer Cross-Linking with Diazo Compounds by C–H Activation and Insertion

“…31−33 A macromolecular cross-linker containing the diazo groups was elegantly reported and applied in the surface modification. 34,35 Herein, we report that the cross-linker containing a multidiazo moiety can be synthesized from commercial diols and triols using esterification and the Regitz diazo transfer reaction (Scheme 1C). The thermal decomposition of the synthesized first and second generations of cross-linker 1G and 2G provides the corresponding bis-carbene that cross-links the linear polymer chains by C−H activation and insertion.…”

“…Therefore, we propose a carbene-mediated polymer cross-linking strategy using compounds that contain two or more carbene precursors. In accordance with this concept, thermal or photochemical conditions were nicely reported to cross-link two polymer chains using bis-diazirine-based cross-linkers; however, tedious synthetic procedures and quantitative loadings (100 wt %) were required for the cross-linkers. − A macromolecular cross-linker containing the diazo groups was elegantly reported and applied in the surface modification. , …”

Thermal Structuring of Surface‐Attached Polymer Networks by C,H Insertion Reactions

“…One approach that circumvents the problem of surface treatment and enables surface attachment with simultaneous crosslinking of the polymer film is based on insertion reactions. [ 8,19–25 ] For this purpose, dormant crosslinker groups are incorporated into the polymer chain during polymerization, which can subsequently be activated by an external stimulus such as thermal, photochemical or mechanical stress, leaving behind a reactive species. [ 8,19,20,22–26 ]…”

“…[ 8,19–25 ] For this purpose, dormant crosslinker groups are incorporated into the polymer chain during polymerization, which can subsequently be activated by an external stimulus such as thermal, photochemical or mechanical stress, leaving behind a reactive species. [ 8,19,20,22–26 ]…”

Tuning the Properties of Surface-Anchored Polymer Networks by Varying the Concentration of a Thermally Activated Cross-Linker, Annealing Time, and Temperature in a One-Pot Reaction

“…Prucker et al have recently revealed a wide range of UV- and thermally active cross-linkers leading to the network formation via C–H insertion cross-linking (CHiC) reaction mechanism. − Accordingly, a precursor copolymer comprising UV-active methacryloyloxybenzophenone (MABP) is deposited on the silicon or a glass substrate precoated with a monolayer of benzophenone-containing silanes . Upon UV irradiation, the benzophenone units present in the polymer and substrate are activated, triggering simultaneous cross-linking and surface-attachment reactions, thus creating surface-attached networks.…”