Polyols from epoxidized soybean oil and alpha hydroxyl acids and their adhesion properties from UV polymerization

Two types of biobased polyols, ESOGA and ESOLA, were synthesized from epoxidized soybean oil (ESO) with glycolic acid (GA) and lactic acid (LA), respectively, using a solvent-free/catalyst-free method. An ESO epoxy conversion rate of over 93% was achieved for both polyols. ESOGA has a weight-/number-average molecular weight (Mw/Mn) of 27,700/3900 g/mol and average hydroxyl functionality (fOH) of 12.9, and ESOLA has Mw/Mn of 8800/3000 g/mol and fOH of 11.7. The structures of the polyols were further characterized with Fourier transform infrared spectroscopy and 1H-nuclear magnetic resonance. Rheology and thermal properties were studied with a rheometer and a differential scanning calorimeter. The polyols were polymerized with ESO to adhesive polymers using UV light in the presence of cationic photoinitiator. The curing rate decreased as the amount of polyol increased for resins based on ESOGA and ESOLA (EGA and ELA). With the same amount of polyol, ELA resins cured faster than EGA resins. The peel strength and tack of EGA and ELA adhesives increased significantly as the ratio of polyol in the resin increased. ELA exhibited obviously higher peel strength and tack than EGA with the same amount of polyol. All resin tapes exhibited high static shear values (20,000+min). Overall, both ESOGA and ESOLA exhibited great potential as polyols for pressure-sensitive adhesive applications.