Isocyanate-free Polyurethane: from synthesis to applications

Polyurethanes (PUs) are currently one of the polymers most used in worldwide for many applications such as rigid and flexible foams, coatings, elastomers, adhesives and sealants. However, the synthesis of conventional polyurethanes relies on isocyanate reactants as crucial starting materials. Toxicity, water-sensitivity and phosgene-based synthesis of isocyanates have required to focused research on more sustainable processes that use ecofriendly and non-hazardous materials. After a first part dedicated to conventional PU technology, this thesis provides an overview of current isocyanate-free pathways for PU synthesis and application, with focus on comparison of conventional PU characteristics with isocyanate-free PU. The first alternative consists in the use of blocked isocyanate which exploits the reversibility of isocyanate bonds through thermal dissociation and regeneration of isocyanate function. The second includes alternative chemistry, focusing on the formation of Non-Isocyanate Polyurethanes (NIPU) via transurethanization and aminolysis of polycyclic carbonates. Their advantages and limitations are outlined and finally the use of non-isocyanate polyurethane to recover applications of classic polyurethane in industry is examined. Blocked isocyanate technology shows different advantages in comparison with conventional polyurethane and has a great potential for further investigation due to the variety of possibilities in isocyanate chemistry. Despite some limitations in terms of kinetics, conversion and molar masses, the reaction of cyclic carbonates and amines appeared as the most promising substitute for the synthesis of non-isocyanate polyurethanes thanks to the possibility of producing hybrid NIPU with other polymers such as polyepoxide, polyacrylates and polysiloxanes which overcome these problems.