Biobased and Aromatic Reversible Thermoset Networks from Condensed Tannins via the Diels−Alder Reaction

Thermo-reversible networks were obtained for the first time from tannins, an aromatic biobased polyphenol, by reacting furan-bearing tannins and telechelic oligomers with maleimide end groups, using the Diels−Alder (DA) reaction. Condensed tannins from mimosa (<i>Acacia mearnsii</i>) were functionalized with furfuryl glycidyl ether and thoroughly characterized by ¹H, ³¹P NMR, and FTIR spectroscopy. The accessibility of the grafted furan groups was confirmed by a model reaction with <i>N</i>-methylmaleimide. Different cross-linked networks were then obtained by DA reaction with three PPO and PPO-<i>b</i>-PEO-<i>b</i>-PPO oligomers and evidenced by FTIR spectroscopy. The thermal properties of the obtained networks were evaluated with differential scanning calorimetry (DSC) and thermogravimetric analysis. Then, the reversibility of the cross-linking was shown by a quick return to the liquid state upon heating at 120 °C. The retro Diels−Alder reaction was studied by size exclusion chromatography and DSC

Combination of Fluorine and Tertiary Amine Activation in Catalyst-Free Thia-Michael Covalent Adaptable Networks

A series of catalyst-free covalent adaptable networks (CANs) have been developed using a reversible thia-Michael reaction activated by fluorine atom substitution and by an intramolecular tertiary amine. The thia-Michael exchange rate was first evaluated by a preliminary molecular study coupled to density functional theory (DFT) calculations. This study enabled us to highlight the necessity of combining fluorine and tertiary amine activation to observe the thia-Michael exchange. Then, by modulating the structure, nature, and functionality of the thiol monomers, a wide range of mechanical properties and thermal properties were achieved. Relationships between the monomer structure and the dynamic properties were also highlighted through the dynamic study of these materials. Finally, the ability of the fluorinated thia-Michael CANs to be reprocessed was assessed by thermal and mechanical analyses of up to three reshaping cycles

Tuning Structure and Rheology of Silica–Latex Nanocomposites with the Molecular Weight of Matrix Chains: A Coupled SAXS–TEM–Simulation Approach

The structure of silica–latex nanocomposites of three matrix chain masses (20, 50, and 160 kg/mol of poly­(ethyl methacrylate)) are studied using a SAXS/TEM approach, coupled via Monte Carlo simulations of scattering of fully polydisperse silica nanoparticle aggregates. At low silica concentrations (1 vol. %), the impact of the matrix chain mass on the structure is quantified in terms of the aggregation number distribution function, highest mass leading to individual dispersion, whereas the lower masses favor the formation of small aggregates. Both simulations for SAXS and TEM give compatible aggregate compacities around 10 vol. %, indicating that the construction algorithm for aggregates is realistic. Our results on structure are rationalized in terms of the critical collision time between nanoparticles due to diffusion in viscous matrices. At higher concentrations, aggregates overlap and form a percolated network, with a smaller and lighter mesh in the presence of high mass polymers. The linear rheology is investigated with oscillatory shear experiments. It shows a feature related to the silica structure at low frequencies, the amplitude of which can be described by two power laws separated by the percolation threshold of aggregates

Terpene and Dextran Renewable Resources for the Synthesis of Amphiphilic Biopolymers

The present work shows the synthesis of amphiphilic polymers based on the hydrophilic dextran and the hydrophobic terpenes as renewable resources. The first step concerns the synthesis of functional terpene molecules by thiol–ene addition chemistry involving amino or carboxylic acid thiols and dihydromyrcenol terpene. The terpene-modified polysaccharides were subsequently synthesized by coupling the functional terpenes with dextran. A reductive amination step produced terpene end-modified dextran with 94% of functionalization, while the esterification step produced three terpene-grafted dextrans with a number of terpene units per dextran of 1, 5, and 10. The amphiphilic renewable grafted polymers were tested as emulsifiers for the stabilization of liquid miniemulsion of terpene droplets dispersed in an aqueous phase. The average hydrodynamic diameter of the stable droplets was observed at about 330 nm

One step closer to coatings applications utilizing self-stratification: effect of rheology modifiers

Self-stratification of model blends of colloidal spheres has recently been demonstrated as a method to form multifunctional coatings in a single pass. However, practical coating formulations are complex fluids with upward of 15 components. Here, we investigate the influence of three different rheology modifiers (RMs) on the stratification of a 10 wt % 7:3 w:w blend of 270 and 96 nm anionic latex particles that do not stratify without RM. However, addition of a high molar mass polysaccharide thickener, xanthan gum, raises the viscosity and corresponding Péclet number enough to achieve small-on-top stratification as demonstrated by atomic force microscopy (AFM) measurements. Importantly, this was possible due to minimal particle-rheology modifier interactions, as demonstrated by the bulk rheology. In contrast, Carbopol 940, a microgel-based RM, was unable to achieve small-on-top stratification despite a comparable increase in viscosity. Instead, pH-dependent interactions with latex particles lead to either laterally segregated structures at pH 3 or a surface enrichment of large particles at pH 8. Strong RM-particle interactions are also observed when the triblock associative RM HEUR10kC12 is used. Here, small-on-top, large-enhanced, and randomly mixed structures were observed at respectively 0.01, 0.1, and 1 wt % HEUR10kC12. Combining rheology, dynamic light scattering, and AFM results allows the mechanisms behind the nonmonotonic stratification in the presence of associative RMs to be elucidated. Our results highlight that stratification can be predicted and controlled for RMs with weak particle interactions, while a strong RM-particle interaction may afford a wider range of stratified structures. This takes a step toward successfully harnessing stratification in coatings formulations.</p