High Tg Polyester Coatings for the Protection of Stones

Copolymers of lactic acid with mandelic or salicylic acid were synthetized through ring opening polymerization (ROP) and tested as protective coatings for stones. Most notably Tg, hydrophobicity and UV barrier properties were increased, making these materials more suitable as protective coating for outdoor stones than poly(lactic acid). A Tg of 76 °C was obtained for the alternating copolymer lactic acid/mandelic acid and it was considerably higher than the one of poly(lactic acid) with similar molecular weight (50-55 °C). Furthermore, the introduction of a perfluorinated moiety as chain-end group, using a perfluoro alcohol as initiator of the ROP process, allowed to increase the hydrophobicity and stability of the new coatings. These polymers showed a good protective efficiency when applied on marble stones and preliminary stability tests under solar light showed low degradation, good stability to photo-oxidative conditions and negligible color changes after an ageing time of 1000 h.