Synthesis and Thiol-Ene Photopolymerization of Bio-Based Hybrid Aromatic-Aliphatic Monomers Derived from Limonene,...

Three novel bio-based monomers were synthesized through an amidation reaction involving allylated derivatives of coumaric, ferulic and phloretic acid and a diamine obtained from a thiol-ene coupling reaction between limonene and cysteamine. The monomers containing the enone bond of the cinnamic moiety underwent photoisomerization and photocycloaddition reactions upon UV light irradiation. All three monomers were photocured via thiol-ene photopolymerization using a glycerol-derived trifunctional thiol, resulting in fully bio-based poly(amide-thioether)s. The polymers derived from monomers that contain the enone bond exhibited glass transition (T_g) temperatures of 85 °C when a stoichiometric ratio of the thiol was used, whereas polymers in which an excess of thiol was used exhibited T_g temperatures of 61 and 74 °C. The higher T_g of the synthesized polymers, compared with other reported polymers produced from thiol-ene photopolymerizations, was attributed to the combination of the aromatic rings of the cinnamic moiety and the cycloaliphatic ring of limonene, as well as the presence of the amide groups in the polymer, which can induce hydrogen bonding. The development of high T_g polymers from bio-based monomers through thiol-ene photopolymerization represents a significant advancement in the polymer synthesis sector, offering an improved performance and sustainability.