Polymer latexes, i.e. dispersion of polymer particles, are the key products of various applications. They are notably used as one of the primary components in the field of coatings, which require the processing of a liquid latex into a polymer film with specific properties such as adhesion, gloss, barrier to gas, wettability, corrosion and solvent resistances. The most widespread industrial process to form polymer latexes is emulsion polymerization, particle stability being ensured by low molar mass surfactants. However, when emulsion polymers undergo film formation, these hydrophilic species are prone to migration and segregation at film interfaces, which negatively impacts some properties. The design of surfactant-free latexes has therefore been a target for both academia and industry for more than 20 years. The use of macromolecular stabilizers strongly anchored to the particle surface at the end of the polymerization can lift some of these issues. Notably, the use of reactive hydrophilic macromolecules that can be involved in emulsion polymerization has received a great deal of attention. The advances achieved in the synthesis of such macromolecules by controlled radical polymerization techniques such as RAFT have pushed this strategy forward, leading to the production of surfactant-free polymer latexes using macromolecular RAFT agents as reactive stabilizers.
Film properties can also be strongly enhanced by crosslinking, which can be induced during film-formation. Various strategies have been developed over the years, leading to films that are permanently crosslinked. However, introducing permanent yet dynamic crosslinks could significantly improve the properties of the films formed, as it is the case for vitrimers. Vitrimers are polymeric networks with exchangeable links such that their topology can rearrange without any loss of network integrity. These dynamic links provide strength akin to thermosets at operating temperature but allow for remolding at elevated temperature. The recent successes achieved in the synthesis of such materials open a new paradigm for polymer latexes and their applications. Indeed, introducing such dynamics crosslinks in the films obtained from polymer latexes will allow preserving the desired chemical and mechanical properties of a crosslinked material, such as chemical, environmental stress cracking, creep and scratch resistances, but will also provide access to additional properties such as self-healing and recycling abilities as well as improved adhesion, all of which being of prime importance for coating applications. In addition, dynamic covalent chemistry can also be used to crosslink materials during their processing, thereby significantly simplifying their synthesis and processing. Such attributes should be of great interest for coatings and dynamic crosslinking could lead to a new process of film formation.
In this context, the aim of DYNAMEX is to design new polymer latexes for the formation of crosslinked films with potential self-healing properties and/or recyclability owing to vitrimer-like properties. To meet these challenges, different surfactant-free polymer latexes incorporating functional groups able to establish dynamic covalent bonds will be synthesized using RAFT and emulsion polymerization. These latexes will be then mixed with either another latex or free (macro)molecules containing the complementary functions needed to trigger the formation of exchangeable links. Adjusting the amount and location of each complementary function will allow us to tune the crosslinking density, and therefore the mechanical properties of the resulting films, as well as the dynamic of exchange. DYNAMEX will thus enable us to demonstrate the applicability of vitrimer chemistry in emulsion polymerization, a typical high volume industrial process, to produce polymer films incorporating dynamic crosslinks with potential new properties.
Madame Muriel LANSALOT (CHIMIE, CATALYSE, POLYMERES ET PROCEDES)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
C3M CHIMIE MOLECULAIRE, MACROMOLECULAIRE, MATERIAUX
C2P2 CHIMIE, CATALYSE, POLYMERES ET PROCEDES
Help of the ANR 333,319 euros
Beginning and duration of the scientific project: September 2019 - 42 Months