Keven Walter

Guaiacol moieties (1‐hydroxy‐2‐methoxy‐benzenes) are among the most abundant structural motifs in renewable biophenolic feedstocks, representing a potential industrial‐scale stream from softwood lignin through biorefinery valorization. Here, the transformative chemistry of masked ortho‐quinones (MoQs) is introduced, yielding reactive guaiacol derivatives to enable thiol‐guaiacol connectivity (TGC) polymers. Phenyliodine(III)diacetate (PIDA) oxidizes guaiacols to chemically pure MoQs within minutes at room temperature, generating activated triguaiacol monomers that undergo thiol‐MoQ Michael‐type polyaddition with multithiols. This bulk polymerization leads to TGC‐adhesives, reaching professional performance lap‐shear strengths up to 16.9 ± 0.9 MPa. The robust strategy is extended to directly activate technical lignin, generating curable multi‐MoQ prepolymers which bond aluminum with lap‐shear strengths of 9.1 ± 0.7 MPa, positioning MoQs as a sustainable platform chemistry to bridge from lignin to high‐performance materials.

The next generation of adhesives requires effective debonding capabilities that can be triggered on demand to enable advanced circular repair and recycling strategies. A new class of lignin‐inspired, two‐component (2K) structural adhesives offers bonding strengths of up to 20 MPa and clean, on‐command electrochemical debonding within 5–30 min. The debonding is induced by a distinct electrochemical oxidation of thiol‐catechol connectivities (TCCs) within the entire adhesive network, enforcing rapid and clean adhesive failure on the cathodic substrate side. The TCC‐functionalities are formed during curing by a thiol‐quinone Michael ‐type polyaddition, reacting polyester‐based trithiols with tris‐quinones as lignin‐inspired minimal building blocks. The structural adhesive can be fine‐tuned by adjusting the formulation. The addition of carbon black and ionic liquids facilitates the desired electrochemical transformation of TCC‐catechols to TCC‐quinones. Applying only 9 V for 5–30 min, leads to clean debonding with 72–86% loss of shear strength. A comprehensive study of curing, bonding, and debonding behavior by rheological, spectroscopic, and electrochemical investigations reveals the debonding mechanism by correlating catechol oxidation to adhesive performance. The electrochemical debonding capability of TCC‐structural adhesives is demonstrated in a functional prototype, where on‐command detachment of a cover glass from a display device is achieved within 6.5 min.

Multifunktionelle ortho‐Chinone werden für die Bildung von Thiol‐Catechol‐Verknüpfungen (engl. thiol‐catechol‐connectivity, TCC) benötigt, sind jedoch empfindlich in der Handhabung. Die elektrochemische Oxidation des Dipeptids DiDOPA vom Catechol zum ortho‐Chinon wird hier mit einer optimierten Umwandlungseffizienz von bis zu 92 % vorgestellt. Die Elektrosynthese erfolgte an kostengünstigen Graphit‐ und Edelstahlelektroden. Durch die elektrochemische Aktivierung werden Chinon‐Lösungen erzeugt, die frei von unerwünschten reaktiven Verbindungen sind, wodurch die anspruchsvolle Isolierung instabiler Chinone entfällt. Die DiDOPA‐Chinone wurden in Polyadditionsreaktionen mit Multithiolen eingesetzt und bildeten Oligomere, die als transiente Enzymstabilisatoren (TES) fungieren. Bei Verwendung der TCC‐TES‐Oligomere als Additive in Hitzebelastungstests wurde ein Stabilisierungseffekt für Tyrosinase beobachtet. Die Anwesenheit der TCC‐TES schützte das Enzym bei thermischem Stress vor Denaturierung und Aktivitätsverlusten.

Multifunctional ortho‐quinones are required for the formation of thiol‐catechol‐connectivities (TCC) but can be delicate to handle. We present the electrochemical oxidation of the dipeptide DiDOPA, achieving up to 92 % conversion efficiency of the catechols to ortho‐quinones. Graphite and stainless steel could be employed as cost‐efficient electrodes. The electrochemical activation yields quinone‐solutions, which are free of undesired reactive compounds and eliminates the challenging step of isolating the reactive quinones. The DiDOPA quinones were employed in polyaddition reactions with multi‐thiols, forming oligomers that functioned as transient enzyme stabilizers (TES). These TCC‐TES‐additives improved the thermal stability and the activity of tyrosinase in heat stress assays.

Debondable pressure‐sensitive adhesives (PSAs) promise access to recyclability in microelectronics in the transition toward a circular economy. Two PSAs were synthesized from a tetravalent thiol star‐polyester forming thiol‐catechol‐connectivities (TCC) with either the biorelated DiDopa‐bisquinone (BY*Q) or the fossil‐based bisquinone A (BQA). The PSAs enable debonding by oxidation of TCC‐catechols to quinones. The extent of debonding efficiency depends on the interaction modes, which are determined by the chemical structure differences of both TCC‐motifs. BY*Q‐TCC‐PSA debonds with exceptional loss of 99 % of its approx. 2 MPa shear strength in glass‐on‐glass junctions. For BQA‐TCC‐PSA, a debonding efficiency of only approx. 60 % was found, irrespective of its initial shear strength, which could be tuned up to approx. 7 MPa. The efficiency of debonding for BY*Q‐TCC‐PSA after TCC‐oxidation is linked to the loss of synergistic interactions without strongly affecting the bulk glue properties, outperforming the purely catechol‐based BQA‐analogue.