Preparation and Characterization of Novel Poly(Thiourethane)-Poly(Isocyanurate) Covalent Adaptable Networks. Effect of the Catalysts.

Poly(thiourethane)-based covalent adaptable networks (CANs) were synthesized by reacting a trimer of hexamethylene diisocyanate (Desmodur® N3300) containing isocyanurate groups in its structure with 1,6-hexanedithiol. The catalysts evaluated for this process included dibutyltin dilaurate (DBTDL), lanthanum triflate (La(OTf) 3 ), and a thermal precursor of 1,8-diazabicyclo[5.4.0]undec-7-ene (BGDBU). The use of DBTDL resulted in the initiation of curing upon mixing, while the other two catalysts exhibited a latency period in the reactive mixture, with curing starting at about 90 °C. Notably, the use of the lanthanum salt produced an additional minor exothermic reaction at 80 °C. This phenomenon corresponds to the trimerization of isocyanates rending isocyanurates, leaving a portion of unreacted thiols.Materials prepared with BGDBU or La(OTf) 3 presented shorter relaxation times than those prepared with DBTDL. Nevertheless, the materials containing the lanthanum salt did not reach complete relaxation, likely due to the reinforcement of the permanent network through increased isocyanurate content. The formation of isocyanurates produced a stoichiometric imbalance, leaving unreacted thiols. This transforms the exchange process into a dual mechanism involving a dissociative process of thiourethanes to isocyanate and thiol, along with an interchange through thiol attacking the thiourethane group. The materials exhibited good recyclability and self-healing characteristics. This article is protected by copyright. All rights reserved.