No abstract

SUMMARY The synthesis of various fluorinated acrylates CH2?CHCOO(CH2)pC,Fk+I and their kinetics of radical homopolymerization are presented. The fluoroacrylated monomers have been prepared in two steps by acrylation of the corresponding halogenated alcohols produced by radical addition of perfluoroalkyl iodides(C,F2,+J) to w-hydroxylated alkenes. The fluorinated acrylates differ from each other in the nature (branched or linear) and the length (n ranging from 1 to 8) of the fluorinated chain and in the nature of the spacer between this fluorinated chain and the ester group (p ranging from 1 to 11). The kinetics of polymerization led to the determination of kp2/kte. These values were compared with those of commercially available fluorinated acrylates and were found to depend upon both the spacer length and the nature of the fluorinated group.

Photopolymerizable clear coatings based on biosourced acrylates, dedicated to the protection of polycarbonate substrates, were studied. The bio-sourced compounds were not based on triglycerides but were smaller, industrially available molecules similar to classical petro-based monomers. Their polymerization kinetics was studied by photo-DSC and was shown to allow high acrylate conversions even at 25 C. Closely related coatings enriched in alkyl segments, or in monoacrylates to decrease the crosslinking density, were compared. The material composition affects its nanomorphology deduced from X-ray diffraction. Although these changes in composition can slightly shift the mechanical relaxation, it remains wide, and the elastic modulus remains high (>10 8 Pa) for all the tested materials. Microscratch experiments highlighted the efficiency of all the new coatings in terms of protection against scratches. Incorporating a monoacrylate, particularly isobornyl acrylate, can improve the scratch resistance especially in terms of critical load (up to 175% increase compared with a classical petro-based coating).

International audienceThe relationships between the composition and the scratch resistance of clear photo-polymerized protective coatings for thermoplastic substrates were studied in relation with their thermomechanical properties. For this purpose, dynamic mechanical analyses of free-standing films were compared to micro-scratch tests of thick or thin coatings deposited on polycarbonate. In these experiments, the depth indented by the tip, the elastic recovery of the material, the residual depth of the scratch, and the load at which the first crack appears, were analyzed. Different coatings close in formulation were studied. First, the proportion of a specific difunctional monomer featuring a hard structure was varied in order to change the crosslinking density of the polymer network. The thermomechanical properties were consequently modified at high temperature, but remained similar at 23 degrees C, whereas at this temperature, the scratch properties of the coating evolved with its composition. The addition of 5 wt% alumina or silica nanopartides did not modify the thermomechanical properties or the scratch resistance of the coatings, even if a more concentrated filler layer was observed near the surface of the coating. Nevertheless, the consequent incorporation of a new diacrylate monomer in the polymer matrix delayed the ductile-brittle transition. Finally the substitution of petro-based monomers by slightly different bio-based compounds led to a change of the scratch behavior of the thickest coatings (150 mu m-thick), and increased the critical load for the thinnest coatings (15 mu m-thick). It comes out that micro-scratch tests allow a finer comparison of the samples