Improving glass transition temperature of unsaturated polyester thermosets: Conventional unsaturated polyester resins

Highly crosslinkable unsaturated polyester resins (UPR) have attracted many interests in the application as reinforced matrix materials. Here, we present a systematical study of the influence of different curing conditions and styrene concentrations on resin viscosity and dynamic‐mechanical properties of the thermoset. The pure maleic Palapreg® P18‐03 was selected as model UPR because of its broad industrial use. By applying newly developed thermal curing profiles (without thermal initiators) and by raising the styrene content, the T g of the network could be increased up to 206/215°C (1/10 Hz). For the first time, a fast curable UPR based on propylene glycol and neopentyl glycol with a T g of up to 215°C is described. A partial substitution of problematic styrene with methylmethacrylate, tert ‐butylacrylate, and maleic anhydride (MA) was studied as well. MA leads to significantly improved resin reactivity. A resin containing 42 wt% styrene and 8 wt% MA yields thermosets with remarkably improved mechanical properties and with a narrower glass transition range compared to the original P18‐03.