Synthesis and Performance of Polyesters with Dopo Substituents for Enhanced Flame Retardancy in Surface Coatings

Abstract

Fires can occur in anywhere and cause death of people, material losses and the loss of unique art/historical works. According to reports, the use of flame retardants greatly prevents the spread of fire. Nowadays, some halogenated flame retardants, such as polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), are banned for use in polymer matrix due to environmental concerns and the toxicity of the gas products formed during combustion. Inorganic based additives such as zinc borate, aluminum trihydrate (ATH) and organophosphorus such as triethyl phosphate (TEP), tris (1-chloro-2-propyl) phosphate (TCPP) are used to provide flame retardant properties to the polymer matrix. However, forming aggregates, leaching out from matrix to the environment with loosing flame retardancy in the longe range is the main concern in this field. One of the main strategy is to synthesize a polymer that shows inherently flame retardancy without addition any other flame retardant. Here, anhydride functional DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide) monomer was synthesized and then used in the polyester formulation. After the synthesis of phosphorus bearing polyester, two component varnish application was conducted using isocyanate curing agent. Thermal properties of the samples was analyzed using thermal gravimetric analysis (TGA). UL94 flammability test was applied to the coated wooden sticks. Surface performance of the phosphorus based varnish was analyzed using pendulum hardness test, gloss test, adhesion test and erichsen scratch test. The results demonstrated a significant reduction in heat release rate and improved char formation, confirming the effectiveness of DOPO-functionalized polyesters in enhancing fire resistance. Moreover, the coatings exhibited excellent adhesion and durability, making them promising candidates for advanced protective applications. This study highlights the potential of phosphorus-based polyesters as sustainable and efficient flame-retardant materials for high-performance coatings.

Keywords: flame retardancy, Phosphorus, Varnish coatings, Polyester