Bio‐Based Epoxy Resins from Estragole: Achieving High Glass Transition Temperatures Comparable to DGEBA and Simultaneously Low Viscosities

ABSTRACT This study covers the synthesis and characterization of two new bio‐based epoxy monomers, diglycidyl‐4‐allylphenol (DG‐4A) and triglycidyl‐diallylphenol (TG‐DA). Both are derived from estragole, a naturally occurring allylbenzene and a major component of the essential oils in basil. The resulting epoxy monomers, with high bio‐contents of 92% (DG‐4A), respectively 72% (TG‐DA), were cured using two different amine hardeners: isophorone diamine (IPDA) and 4,4´‐diaminodiphenyl sulfone (DDS). The curing agents were selected for their distinct properties: IPDA for its bio‐based availability, and DDS for its ability to impart high thermal stability and rigidity. Dynamic mechanical analysis (DMA) showed that DG‐4A/DDS had a high glass transition temperature ( T g ) of 236°C, which can compete with the petrochemical‐based reference system DGEBA/DDS ( T g = 238°C). For the TG‐DA networks, the resulting T g s were 235°C (IPDA) and 300°C (DDS), both were higher than those of the DGEBA reference systems, due to higher crosslinking density. The dynamic viscosities of DG‐4A and TG‐DA were 80 and 15 times lower than those of the reference DGEBA at room temperature. These results suggest that DG‐4A and TG‐DA are sustainable alternatives to DGEBA, as they offer comparable or higher glass transition temperatures while maintaining lower viscosities, making them promising candidates for applications requiring high thermal performance, such as in the aerospace and automotive sectors.