A quantum chemical study on the thermal degradation reaction of polyesters

We carried out a theoretical study on the mechanism of the thermal degradation reaction of polyesters by using the B3LYP level of theory. β elimination reaction of ethylene-, propylene-1,3-, and butylene-1,4-dibenzoates are investigated as model systems for poly(ethylene terephthalate), poly(propylene terephthalate) and poly(butylene terephthalate), respectively. Catalysis mechanism of Sb(OEt)3, Ge(OEt)4, Ti(OEt)4 and Zn(OAc)2 is also investigated. Although the catalysis mechanism in β elimination reaction is generally thought to be electron-withdrawing effect of a Lewis acidity of metal center, the activation energies in this mechanism was calculated to be very similar to those in non-catalyzed reactions and no catalytic effect was observed. We found that β hydrogen abstraction by the alkoxy ligand of catalyst is more favorable reaction path; the activation energy for non-catalyzed thermal degradation reaction of ethylene dibenzoate in vacuo is 51.1 kcal/mol, whereas that in alkoxy ligand mechanism is 43.8 kcal/mol.