Synthesis of mPEG-functionalized betulin-based maleic derivatives and unraveling the effect of PEGylation on dental restorative resins.

As a derivative of bisphenol A (BPA), bisphenol A glycidyl dimethacrylate (Bis-GMA) is questioned regarding its endocrine-disrupting properties. We previously reported a plant-derived monomer, betulin-based maleic diester derivative (MABet), as a substitute for Bis-GMA, but its yellow powdery appearance greatly affected the viscosity and aesthetics of dental resins. Herein, we synthesized three novel types of mPEG-functionalized MABet (PnMABet) by leveraging the active carboxylic acid groups of MABet to undergo a DCC coupling reaction with mPEG variants with diverse repeating ethylene glycol units (n = 7, 12, and 16). Their chemical structures were validated using 1H and 13C NMR spectroscopy, FT-IR spectroscopy, and HR-MS. Afterwards, the PnMABet were incorporated into Bis-GMA-based resins at 10, 30, and 50 wt%. The mechanical performance was firstly evaluated to determine the optimal monomer content. The results showed that all PnMABet monomers were light-yellow liquids. Increasing their concentration from 10, 30, to 50 wt% and the number of repeating units of mPEG from 7, 12, to 16 significantly reduced the mechanical property of resins. Of all groups, 10 wt% addition of P7MABet endowed the resulting 1P7M4B5T resin with the highest flexural and compressive strength (123.2 ± 10.3 MPa; 296.6 ± 27.5 MPa) than the 5B5T control (70.0 ± 6.4 MPa; 230.5 ± 22.5 MPa). This resin also exhibited comparable viscosity, polymerization conversion, cytotoxicity to 5B5T without antibacterial activity. The developed PnMABet have the potential to modulate resin viscosity. Exploring the structure-property relationship is beneficial to realize monomer design and regulate resin properties.