Phenol novolac-based hybrid non-isocyanate polyhydroxy urethane as adhesive: Investigating the effects of amines

Abstract

The introduction of urethane linkages into an epoxy backbone is accepted as a preferred strategy for enhancing the flexibility of the overall system through internal cross-linking. In this work, initially, partial carbonation of an epoxy phenol novolac resin (EPN) was carried out to create a hybrid monomer containing epoxy and cyclic carbonate functionalities (EPNCC). Presence of both functionalities in the same molecule can effectively increase the crosslink density of the resultant system, thereby significantly altering its various physical properties. A series of polyhydroxy urethanes were subsequently been realized by the reaction of EPNCC with different amines such as isophorone diamine, triethylene tetramine, and gaskamine-328. This protocol of making non-isocyanate polyurethanes via aminolysis of cyclic carbonate with amine is a well recognized route that utilizes CO₂ and avoids the use of harmful isocyanates. The impact of different amines on the resultant hybrid polyhydroxyurethane (HPHUs) systems has been evaluated in terms of mechanical, thermal, chemical, and adhesive properties. The optimized system demonstrated good elongation (30–40 %) without comprising the adhesive strength (15–16 MPa) when compared to the parent EPN system. To analyze the hydrogen bonding interactions of the cured system, DFT studies were performed and an optimized structure has been identified for the Gaskamine cured system. The hybrid systems performed admirably as adhesives and can be proposed as good environment friendly candidate for various adhesive applications.