New Polymer Architectures for Architectural Stone Preservation

A series of multifunctional polymeric systems have been designed, synthesized and their effectiveness in modifying the surface properties of different stone types have been evaluated. Both the synthetic strategy and the design of the macromolecular structures are aimed at achieving maximum flexibility in the introduction of structural features that are required to provide the resulting polymers with a range of potential properties. For this purpose, the controlled free radical polymerization of acrylic monomers by the so-called RAFT (Reversible Addition Fragmentation Transfer) technique has been adopted to obtain amphiphilic block copolymers. These may be used either as such in the modification of aqueous dispersions of inorganic nanoparticles (silica, titania, zirconia, zinc oxide among others), resulting in hybrid nanocomposite treatment materials, or as self-assembling reactive precursors for ab initio emulsion polymerizations, leading to the formation of colloidal aqueous dispersions of nanostructured multifunctional polymer nanoparticles. Among the innovative features of the polymers under investigation, the self-stabilisation against photooxidative degradation is worth mentioning as the durability of organic polymers is a well-known open issue in conservation. To achieve enhanced stability, free radical scavenging groups such as Hindered Amine Light Stabilizers (HALS) are introduced in the polymer structure through copolymerization with HALS derivatives. In addition, combination of polymers and UV-blocking inorganic particles (ZnO, TiO2) are also expected to greatly enhance durability. These polymeric materials, and other presently under development, are intended as components of either protective or consolidant treatments to be tested first at a lab scale on various stones (both carbonatic and silicatic), then in situ on 5 different cathedrals distributed throughout Europe and on a contemporary opera theatre.