Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Sulfonic Acids: Computational Evidence for Bifunctional Activation

Abstract

The mechanism of ring-opening of ε-caprolactone by methanol catalyzed by trifluoromethane and methane sulfonic acids has been studied computationally at the DFT level of theory. For both elementary steps, the sulfonic acid was predicted to behave as a bifunctional catalyst. The nucleophilic addition proceeds via activation of both the monomer and the alcohol. The ring-opening involves the cleavage of the endo C-O bond of the tetrahedral intermediate with concomitant proton transfer. In both cases, the sulfonic acid acts as a proton shuttle via its acidic hydrogen atom and basic oxygen atoms. The computed activation barriers are consistent with the relatively fast polymerizations observed experimentally at room temperature with both catalysts.

π‐Plasmon absorbance films of carboxylic functionalized CNTs coupled with renewable PGP platforms

“…The catalyst owns a hydrogen bond acceptor (O atom) and a hydrogen bond donor (H atom), and hence, it can make a bifunctional activation. The ring opening of ε‐caprolactone took place through the cleavage of endo CO with simultaneous proton shuttle between the opened ring and the catalyst . To carry on polymerization, the same mechanism is repeated in the presence of the MSA catalyst, as described in Figure .…”

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“…p‐toluene sulfonic acid acts thus as a “proton shuttle” via its acidic proton and basic oxygen. Similar behaviors were observed in other sulfonic acid catalyzed reactions and notably lactone ring opening polymerization . For the second step when the cleavage of the CO bond of the tetrahedral intermediate and a proton transfer occurs, the barriers are all smaller than for the first step, due to the lower stability of the intermediate adducts when compared with the initial reactants complexes.…”

Extending the Scope of Benign and Thermally Stable Organocatalysts: Application of Dibenzoylmethane for the Bulk Copolymerization of l‐Lactide and ɛ‐Caprolactone

“…This might reflect the involvement of a monomer activated mechanism for which the deviation from the first order kinetic is due to a rate of polymerization not related to the monomer concentration ([M] t ) but to the protonated monomer concentration, [MH + ]. Susperregui et al have evidenced that TfOH eventually behaves as a bifunctional organocatalyst, that is, acting as a proton shuttle both via its acidic hydrogen and its basic oxygen atoms. Analogously, DBM could also act as a bifunctional organocatalyst.…”