Kim K. Oehlenschlaeger

Adaptable Hetero Diels-Alder Networks for Fast Self-Healing under Mild Conditions

A novel adaptable network based on the reversible hetero Diels-Alder reaction of a cyanodithioester and cyclopentadiene is presented. Reversible between 50-120 °C, the adjustable and self-healing features of the network are evidenced via temperature dependent rheology experiments and repetitive tensile tests whereas the networks chemical structure is explored by temperature dependent (1) H MAS-NMR spectroscopy.

Rapid UV light-triggered macromolecular click conjugations via the use of o-quinodimethanes.

Shining a light on click chemistry: The use of UV-radiation as trigger signal provides a facile means to obtain spatial and temporal control over polymer conjugation reactions in addition to providing a further means of achieving orthogonality in click transformations. In the current contribution, UV-radiation was employed to induce a highly efficient Diels-Alder conjugation of polymeric building blocks via the photo-induced in situ formation of highly reactive cis-dienes from a 2-methylbenzophenone precursor.

Light-Induced Modular Ligation of Conventional RAFT Polymers†

Making light work of RAFT conjugation: a non-activated RAFT agent at the end of RAFT polymers can readily be coupled with ortho-quinodimethanes (photoenols) in a photo-triggered Diels-Alder reaction under mild conditions without catalyst. The method is universal and opens the door for the conjugation of a large number of RAFT-prepared polymers with photoenol-functionalized (macro)molecules. (RAFT=reversible addition-fragmentation chain transfer.).

Sunlight-induced crosslinking of 1,2-polybutadienes: access to fluorescent polymer networks

The efficient sunlight-induced crosslinking of 1,2-polybutadienes to generate fluorescent patterns with spatial resolution is reported. The photochemical conjugation method employed is based on a nitrile imine-mediated tetrazole–ene cycloaddition (NITEC) reaction, which proceeds under UV-light irradiation (λmax = 312 nm) at ambient temperature in the absence of any catalyst. The NITEC reaction between 1-pentene and a newly designed di-linker, consisting of two photosensitive diaryl-substituted tetrazoles joined by a tetraethylene glycol spacer, was investigated in an initial study. Detailed characterization of a small molecule model study was performed by size exclusion chromatography (SEC), UV-vis and fluorescence spectroscopy as well as electrospray-ionization mass spectrometry (ESI-MS), which was also employed for monitoring the progress of the reaction (100% conversion in 20 min). Finally, two 1,2-polybutadienes of disparate molar masses were each photocrosslinked with the di-linker. The crosslinking reaction parameters, such as concentration, di-linker fraction and reaction time were optimized via SEC analysis and gravimetric determination of gel fractions. The applicability of the novel crosslinking technology for generating spatially controlled highly fluorescent gel patterns is demonstrated in a solvent-free reaction for 2 h under sunlight. In summary, the current study introduces an efficient light-triggered technology platform for crosslinking polymers carrying non-activated double bonds.

Fast and catalyst-free hetero-Diels-Alder chemistry for on demand cyclable bonding/debonding materials†

A new dithioester possessing a cyano Z-group (cyano-dithioester (CDTE)) has been synthesized via a 2-step, one-pot reaction. The cyano-substituted dithioester has been found to undergo fast reversible hetero-Diels–Alder (HDA) reactions at ambient temperature, without the need for a catalyst, as demonstrated by ESI-MS and UV-Vis experiments. To apply the bonding/debonding on demand system to materials science, a cyano-dithioester di-linker was synthesized and employed as a di-functional dienophile in a HDA-based polymerization reaction with a bis-cyclopentadiene polymer. The reversible bonding of the polymer systems were demonstrated by on-line UV-Vis spectroscopy, on-line NMR spectroscopy, and on-line high temperature DLS, as well as via GPC in situ trapping experiments and high-level ab initio molecular orbital calculations.

State‐of‐the‐Art Analytical Methods for Assessing Dynamic Bonding Soft Matter Materials

Dynamic bonding materials are of high interest in a variety of fields in material science. The reversible nature of certain reaction classes is frequently employed for introducing key material properties such as the capability to self-heal. In addition to the synthetic effort required for designing such materials, their analysis is a highly complex--yet important--endeavor. Herein, we critically review the current state of the art analytical methods and their application in the context of reversible bonding on demand soft matter material characterization for an in-depth performance assessment. The main analytical focus lies on the characterization at the molecular level.

Ambient temperature ligation of diene functional polymer and peptide strands onto cellulose via photochemical and thermal protocols.

In the present contribution, two novel ambient temperature avenues are introduced to functionalize solid cellulose substrates in a modular fashion with synthetic polymer strands (poly(trifluoro ethyl methacrylate), PTFEMA, Mn = 4400 g mol(-1) , Đ = 1.18) and an Arg-Gly-Asp (RGD) containing peptide sequence. Both protocols rely on a hetero Diels-Alder reaction between an activated thiocarbonyl functionality and a diene species. In the first-thermally activated-protocol, the cellulose features surface-expressed thiocarbonylthio compounds, which readily react with diene terminal macromolecules at ambient temperature. In the second protocol, the reactive ene species are photochemically generated based on a phenacyl sulfide-decorated cellulose surface, which upon irradiation expresses highly reactive thioaldehyde species. The generated functional hybrid surfaces are characterized in-depth via ToF-SIMS and XPS analysis, revealing the successful covalent attachment of the grafted materials, including the spatially resolved patterning of both synthetic polymers and peptide strands using the photochemical protocol. The study thus provides a versatile platform technology for solid cellulose substrate modification via efficient thermal and photochemical ligation strategies.