“…4,9,10 Because of this versatility, PU is one of the most produced polymers worldwide, 11 competing with some commodity and specialty chain growth polymers, 12 with an expected production of 22.5 million tons by 2024. 13 Chemically, PU molecules are the main reaction products of the step-growth polymerization between molecules containing isocyanates (-NCO) and active hydrogens, i.e., alcohols. In the simplest reaction scheme, as shown in Scheme 1a, 1,14 urethane linkages are directly formed in one step, with the commonly used diisocyanates in the PU industry being 4,4-methylene diphenyl diisocyanate (4-4′-MDI) and toluene diisocyanate (both 2,6-TDI and 2,4-TDI), as highlighted in Scheme 1b, 5,6 and the most used polyols being polyether-and polyester-polyols.…”