New cross-linking systems using cyclic-carbonate for coatings applications

Coating resins are used in a lot of field of applications (ex : aeronautic, automobile and marine industries, can coil, general industry… etc). For bi-component systems, according to the application and the properties envisaged, isocyanates are used as cross-linkers to allow the formation of urethane linkages. These urethane groups give high properties to the corresponding coatings as hardness, flexibility, gloss, chemical durability… etc. But isocyanates are harmful reactants for humans’ health, or CMR (Carcinogenic, Mutagenic or Toxic to Reproduction) components. Thus, the development of new cross-linking systems with similar properties without the use of isocyanates is a major industrial issue.
The introduction of reactive cyclic carbonate moieties in resins and their cross-linking with polyamines is an interesting alternative to the use of isocyanates. Indeed, the ring opening reaction of cyclic carbonate with amines conducts to the formation of hydroxyurethanes (fig.1) with even better properties than classical urethanes.

Our laboratory is very active in the synthesis and the characterization of new polyhydroxyurethanes, notably for coating applications. The study of the thermal degradation of hydroxyurethanes was performed by our team and has displayed that these compounds do not release isocyanates during thermal degradation contrary to classical urethanes. Among all unsaturated cyclic carbonates monomers which can be used for the synthesis of resins, glycerin carbonate methacrylate (GCMA) is one of the more interesting to study. Its copolymerization in acrylic resins allows the introduction of reactive cyclic carbonate functions which can then react with polyamines in order to form urethane linkages. To determine the synthesis conditions of resins bearing cyclic carbonate moieties, the conventional radical polymerization of GCMA was carefully studied. First the kinetic study for the homopolymerization of GCMA allowed us to highlight the high reactivity of this monomer. Then the copolymerization study of GCMA demonstrated a very good incorporation of this monomer in copolymers. And finally we also fulfilled the study of the cross-linking reaction with amines. All these studies led us to the synthesis of cyclocarbonated resins and the formulation of new isocyanates free urethane coatings.