Bio-inspiration is a key strategy in advanced materials design, with adhesive engineering taking inspiration e.g. from marine mussels. Decades of research led to polymers inspired by mussel glue proteins.

Here, we reveal a chemistry that was overlooked for decades, offering high flexibility and technical scalability to realize greener adhesives.[1] Beyond the family of L-dihydroxyphenylalanine (L-Dopa) bearing polymers, a generic route using thiol-quinone Michael addition to generate thiol-catechol connectivities (TCCs) allowed polymerization of peptides[2] or fully synthetic monomers[3]. The polymerization makes (i) artificial mussel glue proteins with advanced functions as well as (ii) synthetic mussel glue polymers from commodity monomers accessible. Ultimately, a platform of TCC-polymers was established by exploiting on the one hand commodity monomers[4] to address ease of scale-up. On the other hand, the chemistry proved to allow the use of activated lignin as multi-phenols to transform sustainable materials into high performance adhesives.[5] Moreover, abstraction of the essential functionalities responsible for lignin reaction was leading to mini-lignin monomers that enabled high-performance 2K-adhesives bonding via TCCs and effectively debonding on electrochemical command.[6]

Polyurethanes (PUs) are thermosetting materials mainly used in the form of rigid or flexible foams, with a prominent place in construction, transport, and consumer goods industries. Due to their negative health and environmental impacts, conventional PUs are subject to severe regulatory restrictions under the REACH regulation. The substitution of PUs with more sustainable non-isocyanate polyurethanes (NIPUs) is therefore of great interest. Nevertheless, because of their lower reactivity, the curing times of NIPU foams are currently incompatible with the industrial production rates of PU foams, and therefore must be optimised.
In this context, the present work aims at developing new flexible biobased NIPU foams with optimised reactivity, and with equivalent thermal and mechanical properties to standard PU foams. New two-component resins with a high content of renewable materials (>90 wt%) were synthesised from biobased diamines and modified hemp oil, for the production of a wide range of polyhydroxyurethane (PHU) foams. Using an in situ NMR spectroscopy methodology, the influence of the catalyst concentration and nature, and of the reaction temperature, was first highlighted [1]. Using rheometry, very interesting curing times (5 min at 80 °C) were obtained by adjusting the residual epoxy content in the carbonated oil, the amine nature and concentrations, as well as the catalysis conditions. After optimising the expansion method, PHU foams with a glass transition temperature of -25 °C, a density lower than 150 kg.m-3, and a compression set lower than 1 %, were developed, in line with industrial PU specifications.

The growing demand for sustainable and eco-friendly materials has spurred efforts to address both fossil fuel depletion and the accumulation of plastic waste (1). Polyurethanes (PUs), widely used in applications such as foams, coatings, elastomers, adhesives, and biomedicine, represent a significant segment of the polymer market (2). Recent advancements in green PU synthesis focus on replacing fossil-based diisocyanates and polyols with bio-based alternatives to create environmentally friendly polymers without compromising the performance. In this context, we explore the potential of using microbial biopolymer polyhydroxyalkanoates (PHA) and castor oil as polyols for PU synthesis, employing hexamethylenediisocyanate (HMDI) as a crosslinking agent. The PHA was extracted from bacterial biomass using simplified and greener downstream processing using enzymatic breakdown of cells, ensuring an eco-friendly approach throughout the synthesis. The resulting PU films were produced via solvent casting and characterized using ATR-FTIR spectroscopy, SEM, TGA, X-ray diffraction, mechanical testing, and water contact angle measurements. By varying the ratios of castor oil and PHA (100:0, 80:20, 50:50, 20:80 and 0:100) we examined the impact of polyol composition on the properties of the PU films. Our findings highlight the potential of PHA-based PUs as a promising pathway for green, sustainable polyurethane production, contributing to the circular bio-economy and environmentally conscious plastics synthesis.


Acknowledgement: This research was funded by the European Union’s Horizon Europe EIC Pathfinder program, grant number 101046758 (EcoPlastiC).

Recent efforts focus on developing new film-forming agents from renewable resources[1]. This study presents the development of a partially bio-based, waterborne (WB), hydroxylated acrylic resin for use in low volatile organic compounds (VOCs), two-component polyurethane coatings.
The WB system was obtained via a two-step solution radical polymerization in propylene glycol n-butylether: hydrophobic monomers were added first, followed by hydrophilic ones. The resulting acrylic copolymer was then neutralised using amines and dispersed in water, forming core-shell particles with a hydrophobic core and a hydrophilic shell. Reactants nature and equivalents, temperature and amount of solvent were varied. The obtained polyols were characterized by the determination of %Cbio (by ¹⁴C)[2], solid content, pH, acid number, hydroxyl number, Tg, viscosity, particle size, molecular weight and dispersion stability. The rheological behavior of the system was monitored with a cone-plate viscosimeter throughout both the polymerization and dispersion processes. The results were compared with those obtained from synthesizing the resin in solution.
The most promising polyol was combined with a partially bio-based (Cbio: 61%) hydrophilic polyisocyanurate[3] and applied to glass. FT-IR tracked -NCO consumption, while König hardness assessed curing. Hand and mechanical mixing techniques were compared, monitoring particle size, viscosity, %NCO, and pH[4]. Differential scanning calorimetry (DSC) evaluated the curing reaction of the polyol, with and without an accelerant, along with thermal resistance and Tg of the polyurethane[5].
These findings provide valuable insights into the synthesis of environmentally friendly coatings and contribute to the ongoing efforts in the development and characterization of sustainable materials.

For room temperature curing of aliphatic isocyanates, tin-based Lewis acid catalysis is state of the art. This is mainly due to its high activity and its selectivity towards side reactions with water. However, the replacement of tin-based catalysts for toxicological and environmental issues is an important goal for the practical application of this chemistry.[1,2]

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Typical reaction under investigation; reaction conditions: 1 equiv. isocyanate, 1.5 equiv. alcohol, 0.01 equiv. Lewis base, room temperature, solvent free. Alcohols with different pKa (DMSO) were tested.[3]

In this contribution we present our results on Lewis base catalysis for the reaction of aliphatic isocyanates with aliphatic and aromatic alcohols at room temperature under solvent-free conditions. Emphasis is placed on uncovering the role of the electronic properties of the alcohol on the rate of the reaction using different Lewis bases and the Lewis acid dibutylin dilaureate (DBTL) as the reference. The results for primary aliphatic alcohols showed that none of the Lewis bases could compete favorably with DBTL in catalytic activity. However, a strong dependence of the alcohols’ acidity on the reaction rate was found. In case of Lewis base catalysis, more acidic alcohols react much faster than less acidic ones. An opposite trend is observed with DBTL. In this case, the speed of the reaction becomes higher with increasing nucleophilicity of the alcohols.