Marlène Lejars

Actuellement, il existe deux types de peintures anti-salissures marines sur le marché : - Les Self-Polishing Coatings (SPC), revêtements auto-polissants à base de liants polymères hydrolysables, efficaces par relargage de biocides dans le milieu marin mais toxiques pour l’environnement ; - Les Fouling Release Coatings (FRC), revêtements hydrophobes à base de silicone, sans biocides, qui limitent la force d’adhésion des salissures mais ne sont pas efficaces en mode statique.L’objectif de cette étude est d’élaborer des peintures anti-salissures marines hybrides FRC/SPC. Pour ce faire, des polymères diblocs à la fois hydrolysables et présentant une faible énergie de surface ont été synthétisés et caractérisés puis utilisés en tant que liants dans la formulation de peintures anti-salissures marines.Le procédé de polymérisation RAFT a été employé afin de synthétiser des polymères avec une architecture et une masse molaire contrôlée. Deux approches ont été abordées :- Des polymères ont été synthétisés à base de monomères de faible énergie de surface et hydrolysables (le méthacrylate de (heptaméthyl-trisiloxy)diméthylsilyle et le méthacrylate de bis(triméthylsilyloxy)méthylsilyle) avec un co-monomère méthacrylate de méthyle ou méthacrylate de butyle. Il a notamment pu être montré que les copolymères de structure dibloc présentent une énergie de surface plus faible que les copolymères statistiques.- Des polymères ont été synthétisés à partir de monomères hydrolysables tel que le méthacrylate de tert-butyldiméthylsilyle et de monomères de faible énergie de surface tel que le méthacrylate de poly(diméthyl-siloxane).Les propriétés d’érosion (type SPC) et d’énergie de surface (type FRC) ont été étudiées pour les liants seuls et les peintures formulées, avant et pendant leur immersion en eau de mer artificielle. L’efficacité anti-salissures marines des peintures formulées a été évaluée lors de leur immersion in-situ en Mer Méditerranée.

Fouling Release Coatings are marine antifouling coatings based on silicone elastomers. Contrary to commonly used biocide-based antifouling coatings, they do not release biocides into the marine environment, however, they suffer from poor antifouling efficacy during idle periods. To improve their antifouling performances in static conditions, various amounts of hydrolyzable polymers were incorporated within a silicone matrix. These hydrolyzable polymers were chosen for the well-known hydrolytic degradation mechanism of their main chain, e.g. poly(ε-caprolactone) (PCL), or of their ester pending groups, e.g. poly(bis(trimethylsilyloxy)methylsilyl methacrylate) (PMATM2). The degradation kinetics of such hydrolyzable silicone coatings were assessed by mass loss measurements during immersion in deionized water. Coatings containing PMATM2 exhibited a maximum mass loss after 12 weeks, whereas PCL-based coatings showed no significant mass loss after 24 weeks. Dynamic contact angle measurements revealed the modifications of the coatings surface chemistry with an amphiphilic behavior after water exposure. The attachment of macrofoulers on these coatings were evaluated by field tests in the Mediterranean Sea, demonstrating the short or long-term antifouling effect of these hydrolyzable polymers embedded in the silicone matrix. The settlement of A. amphitrite barnacles on the different coatings indicated inhospitable behaviors towards larval barnacles for coatings with at least 15 wt % of additives.

Much current research is focused on preventing and controlling the natural process of colonization by marine organisms of surfaces submerged in seawater. Previously, the authors’ laboratory has reported the synthesis and the full physico-chemical characterization of homopolymers obtained from 1-ferrocenylmethyl methacrylate (FMMA), 2-(ferrocenylmethoxy)ethyl methacrylate (FMOEMA), and 3-(ferrocenylmethoxy)propyl methacrylate (FMOPMA). Here, the bacterial anti-adhesion activity of these homopolymers (pFMMA, pFMOEMA and pFMOPMA) is reported when stimulated in 96-well microplates containing a printed electrochemical cell in each well. Polymers were deposited on the printed carbon working electrode of each well in two columns each comprising eight wells. Their electrochemical anti-adhesion properties were evaluated by inoculating a marine biofilm forming bacterial strain, Pseudoalteramonas lipolytica, in each well and then applying recurrent scans for 15 h. The results revealed an intrinsic anti-adhesion activity of all the polymers. This activity was amplified by a factor of 10 when potential recurrent scans were applied.

A series of new alkoxy-ferrocene methacrylates was polymerized by the raft process leading to redox polymers with low T_g values.

Statistical and diblock copolymers of bis(trimethylsiloxy)methylsilyl methacrylate (MATM2), a hydrolyzable monomer containing a silylester and a siloxane group, and methyl methacrylate (MMA) were synthesized by the RAFT process. The controlled character of the MATM2 RAFT polymerization using 2-cyanoprop-2-yl-dithiobenzoate (CPDB) or S-(2-cyanoprop-2-yl)-S-dodecyltrithiocarbonate as chain transfer agents was assessed by linear pseudo-first-order kinetics, linear molar mass growth with monomer conversion and low molar-mass dispersity. The hydrolysis kinetics of pMATM2 homopolymers was investigated by in situ¹H-NMR and compared to several methacrylic homopolymers bearing hydrolyzable tri-alkylsilylester side groups. pMATM2-block-pMMA diblock copolymers were synthesized by in situ chain extension with methyl methacrylate, using pMATM2-CPDB as a macro-CTA. p(MATM2-stat-MMA) statistical copolymers were synthesized by simultaneous polymerization of MATM2 and MMA by the RAFT process. The monomer reactivity ratios for MATM2 (r₁ = 1.29) and MMA (r₂ = 0.62) were obtained from the Mayo Lewis equation using the least-squares method. All the copolymers synthesized by the RAFT process had molar masses close to the targeted values and low dispersities (Đ_M < 1.15). DSC analysis and contact angle measurements revealed the influence of the copolymer microstructure (statistical or diblock) on their glass transition temperature and surface energy.

Graft copolymers of hydrolyzable tert-butyldimethylsilyl methacrylate (TBDMSiMA) and low surface energy poly(dimethylsiloxane) methacrylate of 1000 g mol⁻¹ (PDMSMA1k) and 5000 g mol⁻¹ (PDMSMA5k) were synthesized by the RAFT process, using 2-cyanoprop-2-yl-dithiobenzoate (CPDB) as a chain transfer agent, at 70 °C, in xylene. The homopolymerizations of each monomer were first studied, demonstrating their control by the RAFT process. Simultaneous copolymerizations of TBDMSiMA and PDMSMA led to gradient graft copolymers as demonstrated by the determination of monomer reactivity ratios by the Jaacks method. Sequential polymerizations led to diblock or blocky graft copolymers depending on the order of addition of each monomer. All the copolymerizations were controlled by the RAFT process with molecular weight values close to the theoretical values, together with monomodal and narrow distributions (PDI < 1.2). The graft copolymers exhibited two glass transition temperatures, corresponding to the PDMS- and pTBDMSiMA-enriched phases, respectively. The PDMS side chain distribution and length were shown to be significant parameters influencing the thermal behavior of the copolymers, their low surface energy and their erosion properties in artificial seawater. These latter properties make these graft copolymers suitable for applications as binders for self-polishing/fouling release hybrid antifouling coatings.