Supramolecular control of propagation in cationic polymerization of room temperature curable epoxy compositions

The cationic ring-opening polymerization (ROP) of room temperature curable epoxy compositions was investigated in the presence of protic (alcohols), weakly chelating (linear polyethers), and strongly chelating (crown ethers) species. Epoxide conversion and gelation were monitored through infrared and rheological measurements. We demonstrate that the propensity of hydroxyl moieties to promote the activated monomer (AM) mechanism and the chelating ability of polyether groups toward the cationic species involved in this propagation mode can be combined to control two fundamental parameters of the gelation process of epoxy resins, the gel time (t_gel) and the critical conversion (conversion at the gel point, x_gel), by adequately adapting the amount of these additives. In the case of crown ether, a strong synergy between these two control tools was found and interpreted by the prolonged stabilization of protons involved in chain transfers, in the form of dormant supramolecular host-guest complexes. These results underline the potential of this new approach to control both the kinetic and architecture of epoxy growing network.