This action is of great importance for the synthesis of unsaturated polyesters resins obtained by a mixture of acids and glycols derived from renewable resources. Unsaturated polyester resins (UPR) are the most widely used in composites, making up more than of 80% of all thermoset resins (the rest being mainly epoxies, acrylics, imides, phenolics, and urethanes). While the UPR market was hit by the recession in 2008-2009, it is currently growing at almost 10% per year and expected to reach 0.5 billion by 2015.
The condensation reactions under conventional conditions can be applied to prepare different IA-based unsaturated polyester resins. Accordingly to this, some polyester resins containing glycols or diacids derived from renewable resources, in combination with IA, can be synthesized by different routes. The conventional two-step polycondensation reactions can be applied to production of necessary amounts of IA-based unsaturated polyester to begin other subsequent technical actions. An example of some possible chemical structures of unsaturated polyesters and copolyesters, where the unsaturation of maleic anhydride (see scheme C3.1) has been replaced with that derived from itaconic acid. The two step polycondensation reactions can be applied by adding a stoichiometric feed of IA and glycol to the reactor at a temperature above 120°C under reflux conditions. Under these reaction conditions the temperature reaches 150/160°C and after 1-2 h a prepolymer with low molecular weight is obtained. At this stage a catalyst can be added to reaction mixture and the water can be eliminated at reduced pressure (under vacuum). After 6-8 h a high conversion degree (above 0.95/0.97) of acidic groups can be reached giving UPR resins with number average molecular weights (Mn) ranging from 8.000 and 15.000 Da (Dalton). Under the same experimental conditions some copolyesters can be obtained varying the molar ratio between the used glycols. The selection of the used glycols is very important to claim the fully biobased UPR resins.
Since ethylene glycol (EG) and monopropylen glycol (MPG) are commercially available from renewable resources from European suppliers, these two glycol are the best candidates for the synthesis of fully biobased polyesters and copolyesters resins (BioUPR).
It is of great importance the existence of itaconic acid unsaturations in the polyester chains to combine the bioUPR with high reactivity to mono- and multi-(meth)acrylated monomers and oligomers for replacing the styrene during the thermo- and photo-initiated crosslinking reactions for the preparation of coatings, adhesives, inks and biocomposites.
Beneficiary responsible for implementation: POLYNT