Synthesis of oleic-based primary glycol with high molecular weight for bio-based waterborne polyurethane

Oleic acid, as a renewable resource, exists in almost every vegetable oil, especially olive and camellia oils, which has promising prospects for the preparation of bio-based polymers. In this study, a novel oleic-based primary glycol (OPG) was synthesized from methyl oleate (MO, derived from vegetable oil) via Claisen condensation and thiol-ene photo-click reactions and used as an alternative to petroleum-based glycol for the preparation of bio-based waterborne polyurethane (BWPU), and the differences in reactivity between the OPG and petroleum-based polypropylene glycol (PPG) and properties between BWPU and petroleum-based waterborne polyurethane (PWPU) were investigated. The yield of OPG was approximately 90%, the degree of functionality was 2.0, the hydroxyl value was about 155 mg KOH g−1 and the molecular weight (Mw) varied from 296 g mol−1 to 560 g mol−1 and 716 g mol−1 after the chain extension of Claisen condensation and thiol-ene photo-click reactions. In comparison with PPG, OPG exhibited lower activation energy towards IPDI, and the values showed an order of OPG (Ea/Eo=71.25/74.20 kJ mol−1) < PPG600 (Ea/Eo=106.83/108.03 kJ mol−1) < PPG1000 (Ea/Eo=129.20/129.37 kJ mol−1). Correspondingly, the end point of pre-polymerization appeared in 80 min for OPG and 420 min, 840 min for PPG600 and PPG1000 at 80 °C without catalyst, demonstrating that OPG had higher reactivity. Because of the difference in hydrophobicity, the minimum amount of hydrophilic extender used to obtain stable WPU emulsions was 7 wt% for OPG and 3.5 wt% for PPG respectively. The resulting BWPU films possessed good mechanical properties, including higher tensile strength (19.78 MPa) and Young’s modulus (206.61 MPa). But the thermal stability (Td5% ≤ 250 ℃) and low temperature resistance (Tg ≥ 28 ℃) of BWPU films were inferior to that of PWPU films.