Unsaturated polyester resins with low- viscosity: Preparation and mechanical properties enhancement by isophorone diisocyanate (IPDI) modification

Durable unsaturated polyester resins (UPRs) with low-viscosity are essential for scaling up the production of down-streamed industrial products. Yet, lower viscosity usually means the compromise of some basic properties of cured materials such as reduced toughness and decreased heat tolerance. In this study, a series of UPRs with viscosities suitable for the vacuum infusion molding process (VIMP), a novel but promising technique for material molding at industry-scales, were successfully synthesized by simply controlling the amount of alcohol used in reactants. Isophorone diisocyanate (IPDI), for the first time, was applied during the curing of the unsaturated polyester to enhance the physical performances of thus-generated UPRs. Characterizations were performed to study the changes in resin structure after modification, and the effects of the addition amount (mass fraction) of IPDI on the properties of UPRs castings were also discussed. Results showed that IPDI could enhance the mechanical properties of UPR castings by more than 30%, with the optimal performances (tensile strength, 55.95 MPa; bending strength, 120.11 MPa; tensile modulus, 3.34 GPa; flexural modulus, 2.97 GPa and Barcol hardness, 43 HBa) obtained when 9 wt% of IPDI was used. The thermal stability of the castings could also be enhanced in the presence of IPDI. Therefore, the proposed strategy may provide a simple avenue for preparing performance enhanced low-viscosity UPRs to meet industrial requirements.