Acylated Acetals: A Chemical Platform for Advanced Covalent Adaptable Networks and Isoporous Functional Membranes – ACECANISM

Acylated acetals (AcAc, also known as hemiacetal esters) and hybrid AcAc constitute a very interesting class of compounds which have been largely underused and understudied. They can be seen as a subclass of acetals in which one of the constitutive RO– group is replaced by an ester (RCOO–). The vast majority of studies reported thus far deal with the oxygen-based function. Compared to acetals or thioacetals, AcAc are less hydrolytically stable and more prone to nucleophilic attack. They are easily formed by addition of carboxylic acids to vinyl ethers and spontaneously dissociate upon heating. The main reactivity pathways of AcAc, namely (i) thermal reversion to a carboxylic acid and a vinyl ether, (ii) hydrolysis under mild to strong acidic conditions to release a carboxylic acid, an aldehyde and an alcohol and (iii) reaction with other weak nucleophiles such as carboxylic acids.
Nevertheless, the scientific corpus dedicated to these functional groups is very small compared to other chemical groups and fundamental structure-reactivity studies are very rare and rather old. We recently demonstrated that AcAc readily undergo carboxylic acid exchange at ambient temperature. This important discovery combined with the spontaneous thermal dissociation make this chemical function unique and open a wealth of opportunities in chemistry and polymer science & technology. ACECANISM will pursue 3 ambitious objectives: 1) Explore the chemistry of hybrid and standard acylated acetals (AcAc) to better understand the structure–property relationship of these chemical groups and ultimately be able to tune these properties, 2) Design and examine novel AcAc-based covalent adaptable networks endowed with unprecedented viscosity profile, and 3) Harness the dissociation properties of AcAc to prepare high performance functional ultrafiltration membranes.
A first WP will be dedicated to the preparation of novel AcAc featuring innovative substitution pattern and progressive replacements of the oxygen atoms by sulfur atoms. All these variations aim at modulating the thermal and hydrolytic stabilities as well as the reactivity towards nucleophiles of the AcAc. This reactivity pattern will be studied by combining DFT study and experimental approach to determine the most plausible mechanistic pathways and to compare the stability/reactivity of the different AcAc depending on their structural features. Finally, the most promising structures will be elaborated as monomers for the synthesis of degradable linear polymers. The second WP will deal with the synthesis of vitrimers based on AcAc reversible linkages. The first CANs will be prepared using simple oxygenated AcAc and low molar mass synthons in order to examine the vitrimer behavior of such readily available networks, as well as to assess their stability. A second step will be to prepare hydrolytically stable AcAc-based vitrimers from hydrophobic prepolymers featuring carboxylic acids that will be cross-linked using tri(vinylethers). Finally, using the most stable structures, vitrimers featuring original AcAc groups will also be prepared, with the ultimate goal of preparing networks exhibiting a dual viscosity dependence arising from the associative exchange of acids and the reversible dissociation of AcAc linkages at high temperature. The third research WP is dedicated to the use of AcAc dissociative chemistry to prepare high performance ultrafiltration membranes. The combination of the efficient non-solvent induced phase separation membrane fabrication process and of the self assembly of block copolymers featuring a labile AcAc linkage will lead after hydrolysis to isoporous membranes with pores decorated with carboxylic acid functional groups. These acids wil then be used as chemical handles to add supplementary properties to these membranes. ACECANISM will train 2 PhD students ans one postdoctoral fellow at the top level of organic chemistry, polymer materials, and membrane sciences.