DESIGN OF ADVANCED STRUCTURED FUNCTIONAL POLYMER SURFACES FROM PHOTO-ACTIVE POLYMER NANOPARTICLES – FUNPOLYSURF

Self-stabilized nanoparticles consisting of a soft hydrophobic poly(alkyl acrylate) core and a rigid hydrophilic poly(ammonium acrylate) shell were prepared by the polymerization-induced self-assembly (PISA) process in emulsion. This solvent- and surfactant-free “green” process consists in the use of a hydrophilic macromolecular control agent for the emulsion polymerization of a hydrophobic monomer. Amphiphilic block copolymers form by reversible addition-fragmentation transfer (RAFT) polymerization, and simultaneously self-assemble in water to form latex particles dispersed in an aqueous phase. In order to introduce the organic photosensitiser, namely Rose Bengal, within the polymer core-shell particles, Rose Bengal-based monomers were synthesized. The RAFT copolymerization of a Rose Bengal-based monomer with acrylic acid allowed to obtain first photoactive hydrophilic copolymers, and then nanoparticles containing the Rose Bengal in the shell. On the other hand, the copolymerization of a Rose Bengal-based monomer with the alkyl acrylate (ethyl acrylate and/or n-butyl acrylate) in emulsion in the presence of living poly(acrylic acid) allowed obtaining particles with Rose Bengal in the core. Monodisperse, stable and photoactive latexes were prepared and well-structured photoactive films were obtained as highlighted by AFM and SAXS characterization. Mechanical properties were evaluated by cyclic uniaxial tensile tests and showed a range of interested properties for soft coatings. Interestingly, mechanical properties were tuned by the copolymer structure and this control was maintained in the presence of photosensitizer. The photoactivity of latexes and films containing Rose Bengal was proven by an indirect method consisting in the degradation, under visible irradiation, of singlet oxygen specific probes by the photoactive polymer materials.

Aqueous dispersions of polymer particles, stable and photoactive, have been developed within the framework of the FUNPOLYSURF project. Well-structured photoactive films with remarkable and modular mechanical properties have been prepared by controlled deposition and drying of the latexes. The photoactivity of latexes and films containing the Rose Bengal photosensitizer has been proven by interfacial production of singlet oxygen under light irradiation of latexes or films in the visible range. This project made it possible to demonstrate all the advantages of PISA emulsion polymerization to transfer both photoactive properties and modular mechanical properties to the polymer film, two important criteria for the development of specialty materials.

The fact that the manufacturing process for photoactive colloids and polymer films and the control of their mechanical properties was well established during the FUNPOLYSURF project, offers particularly interesting perspectives for developing interfacial photochemical processes for two specific applications :
1) to create bactericidal coatings under light irradiation
2) to allow the intensification of continuous photooxygenation processes

In order to develop these perspectives, the APOCOLIPS (Advanced functional POlymer COLloids with hIgh Photo-oxidative propertieS) project was submitted in 2019 as part of the European call for projects H2020-MSCA-IF-2019. The latter was selected in February 2020 by the European Commission with a score of 95.4%. The project led by a candidate in collaboration with Dr. Maud Save (IPREM, CNRS / UPPA) includes the following partners:
- Ulster University, UK to assess the bactericidal properties under irradiation in partnership with Dr. Pilar Fernandez-Ibañez.
- LGC-ENSIACET-CNRS (Toulouse) for the intensification of photooxygenation processes in partnership with Dr. Karine Loubière.

“Synthesis of Film-Forming Photoactive Latex Particles by Emulsion Polymerization-Induced Self-Assembly to produce singlet oxygen”
Charlène Boussiron, Mickaël Le Bechec, Luca Petrizza, Julia Sabalot, Sylvie Lacombe,* Maud Save* Macromol. Rapid. Commun. 2019, 40, p 1800329. doi.org/10.1002/marc.201800329

2 articles are in preparation, one will be submitted to a special volume on PISA (RSC editor)

Les travaux de FUNPOLYSURF ont été présentés lors de 4 conférences internationales et 3 conférences nationales.

The objective of the project is to produce novel advanced structured polymer films with both photo-activity and outstanding mechanical properties by simple casting from an aqueous dispersion of colloids. For that purpose, well-defined self-stabilized nanoparticles, made of a hydrophobic core and a covalently linked hydrophilic shell containing the organic photosensitizer units, will be synthesized by emulsion polymerization induced by copolymer self-assembly, an eco-friendly process free of solvent and surfactant. The originality of the project rests on three integrated pillars: 1) the controlled and versatile synthesis of the photo-active polymer particles by polymerization in aqueous dispersed media, 2) the characterization of the internal structure (by fluorescence microscopy, atomic force microscopy), the mechanical properties and water-resistance (for transparency) of the polymer films, which are important parameters to assess the application range, 3) the capability of the polymer coating to produce singlet oxygen under irradiation, investigated by fluorescent singlet oxygen probe and by the propensity to perform photo-induced oxidation reactions of organic molecules at the solid/liquid interface. Since the in-situ produced singlet oxygen has an antimicrobial activity, the project meets a societal challenge by designing functional surfaces for healthcare facilities or food packaging requiring antimicrobial properties. The strength of the project is the combination of innovative chemistry with characterization of passive and active properties to produce novel photo-active coatings with mechanical properties compatible with an application.