Biobased vinyl levulinate as styrene replacement for unsaturated polyester resins

Vinyl levulinate (VL) is used as a biobased reactive diluent in styrene (St)‐free unsaturated polyester resins (UPR). The reactivity ratios for the radical copolymerization of VL with diethyl fumarate (DEF) are determined by the Jaacks method ( r VL = 0.01 and r DEF = 0.81 at 60 °C in DMSO‐ d 6 ). The properties of UPRs having a stoichiometric ratio between unsaturated groups from the UPR and either St or VL are compared. Defect‐free, slightly yellow, transparent, and rigid thermosets are obtained after a mild curing cycle. Due to unfavorable reactivity ratios about 5.5 wt % of unpolymerized VL remains inside the network and acts as plasticizer. Consequently, compared with St‐based ones, VL‐based UPRs exhibit lower α relaxation ( T α = 180 and 100 °C, respectively), lower elastic moduli at the rubbery plateau ( G ′ = 10 8 and 10 7 Pa) and lower mechanical properties as measured by three points bending tests. Strain at break ( ε f = 1.8 ± 0.2%) and Charpy impact strength (∼2.7 ± 0.3 kJ m −2 ) are comparable independently of the RD chemical nature.