High glass transition temperature polyester coatings for the protection of stones

Abstract

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, glass transition temperature (T g ), hydrophobicity, and UV barrier properties were increased, making these materials more suitable as protective coating for outdoor stones than poly(lactic acid). A T g of 768C 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 (50-558C). 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 aging time of 1000 h.

Aromatic triblock polymers from natural sources as protective coatings for stone surfaces

“…The random configuration of the carbon atoms in the monomers led to amorphous materials lacking of any crystalline domain. The polymers showed only a T g from glassy to amorphous state and no crystallization ( T c ) or melting temperature ( T m ) (Table ), and this behavior was already observed in a previous work using PMGLY and SALD monomers …”

“…Monomers were synthesized following the procedure reported in a previous article, using l ‐LD, (S)‐mandelic acid, and salicylic acid as starting materials, thus monomers were obtained having the same characteristics of those previously reported …”

“…The previously reported polymerization procedure was followed using FLK‐OH instead of perfluorooctyl alcohol as chain initiator. In this way PMGLY‐FLK‐PMGLY and SALD‐FLK‐SALD polymers were obtained and their characteristics are reported in Table .…”

“…However, the T g of these polymers was in the range between 25 and 55 °C, potentially causing the loss of the polymer film or the adhesion of particulate on the surface of coated stones. To overcome this problem, the potential employment of high T g aromatic polyester coatings was tested using lactide/mandelide copolymers, containing a perfluoroalkyl moiety as a chain‐end group. These polymers showed a high T g and a significant increase of the hydrophobicity over conventional PLA showing a broad range of applications.…”

Ring‐Opening Polymerization of a New Diester Cyclic Dimer of Mandelic and Glycolic Acid: An Efficient Synthesis Method for Derivatives of Amorphous Polyglycolide with High Tg

“…Although, the ROP of Ph‐DXO is managed under milder conditions than the ROP of OCA, it results in occurring racemization to produce atactic tacticity to attain amorphous characteristics. A partial incorporation of a mandelate unit (M) sequence into PLA was attained by ROP of (3S)‐6‐methyl‐3‐phenyl‐1,4‐dioxan‐2,5‐dione, and the resulting poly(mandelate‐ co ‐lactate) showed a T g of 76 °C as compared to the T g of 55 °C of conventional PLA . Therefore, the reports mentioned above prove that the incorporation of a M unit into a polylactone can improve thermal properties, specifically T g .…”