Synthesis and characterization of molecularly hybrid bisphenols derived from lignin and CNSL: Application in thermosetting resins

Commercially available methacrylates often contain derivates of bisphenol A (BPA), a known human endocrine disruptor and petrochemical derived compound; therefore, alternatives are being investigated to increase sustainability and reduce toxicity. An asymmetric, bio-based bisphenol, VAC, was synthesized via an electrophilic aromatic condensation of vanillyl alcohol and cardanol. The alkyl side chain of VAC was subsequently hydrogenated to yield VAHC to determine the effects of side chain unsaturation on material properties. These bisphenols were methacrylated to prepare VACDM and VAHCDM, blended with a reactive diluent, cured, and compared to BPA dimethacrylate (BPADM), bio-based bisguaiacol dimethacrylate (BGDM), and a commercial BPA based vinyl ester (VE828). Resins containing VACDM and VAHCDM have reduced viscosities relative to BGDM and both BPA-based dimethacrylates, and the unsaturation on the side chain was shown to provide further reduced viscosities. Cured resins with VACDM and VAHCDM exhibit directly comparable thermal stability in both inert and oxidative environments, and decreased glass-transition temperatures due to increased aliphatic character relative to BPA-based resins. The toughness of the thermosets comprised of the bio-based bisphenols were greater than that of BPADM, where the alkyl substituent was shown to impart toughness into the network, yet the level of side chain saturation shows minimal effect on fracture toughness.