Development of hesperetin methacrylates and their high performance thermosets

Hesperetin based monomers substituted to varying degrees of methacrylate functionality were synthesized namely trimethacrylate, dimethacrylate and monomethacrylated hesperetin monomers, HTM, HDM and HMM respectively. Resins employing reactive diluents 4-acryloylmorpholine (4AM) and styrene (Sty) were formulated. Resin formulations were determined to be Newtonian fluids with viscosities below 800 cP. Thermosets of hesperetin monomers were produced with glass transition temperature (T_g) values up to 225°C. Ultimate strength up to 20 MPa and tensile modulus of 5.0 GPa were also observed. Additionally, thermosets with char yield near 30% were measured. Char yield, ultimate strength and tensile modulus of hesperetin based thermosets were superior to those derived from the petrochemical bisphenol A dimethacrylate (BPAM). However, thermosets that employed hesperetin derived monomers displayed properties that were less than expected compared to Bicerano model predictions. Also, select HTM:Sty thermosets displayed a noticeable holographic type morphology. Reactivity ratios, spectroscopy, microscopy and structure property relationships indicated that poor copolymerization behavior during cure and high degrees of crosslinking during postcure were responsible for the microcrack formation in the material. This also caused the observed morphology and resulted in reduced properties relative to Bicerano predictions.