Rapidly synthesized, self-blowing, non-isocyanate polyurethane network foams with reprocessing to bulk networks via hydroxyurethane dynamic chemistry

Abstract

Polyurethanes are produced from reactions of isocyanates with alcohols and are most commonly made as cross-linked networks to produce foams. Polyhydroxyurethanes (PHUs) are non-isocyanate polyurethane (NIPU) materials with promising potential as benign alternatives to isocyanate-based polyurethanes. We have developed a rheology-guided, rapid preparation of reprocessable self-blowing PHU foams by decoupling the aminolysis and thiol-decarboxylation of cyclic carbonates, allowing for dramatic reduction of reaction times from 20 h to 30 min to achieve foams without sacrificing morphological and physical properties. We studied the structure–property relationships in network PHU foams by systematically varying the thiol concentrations and demonstrated highly tunable morphological properties, including cell density, cell diameter, and open-cell ratio, and mechanical properties associated with semi-rigid and flexible foams. To address the sustainability challenges of network foams, the dynamic covalent PHU foams were melt-reprocessed into bulk films with full recovery of cross-link density. We further found that the relative modulus–relative density relationship of our foams obeys the cubic cell model proposed by Gibson and Ashby, which was applied to predict and tailor properties of new PHU foams. This study highlights the design and rapid synthesis of highly tunable and dynamic PHU foams with promising sustainability aspects.