Shape memory crosslinked polyurethanes containing thermoreversible Diels Alder couplings
Crosslinked polyurethanes (PUs) containing irreversible (allophanate) and reversible Diels Alder chemical bonds were synthesized using various diisocyanates (methylene diphenyl diisocyanate MDI, 1,6 hexamethylenediisocyanate HDI) and poly(e caprolactone) (PCL) with different molecular weights (Mn 10 kg/mol, 25 kg/mol, 50 kg/mol) as diol component. The melting/crystallization of PCL and the reversible DA bonds acted as temperature activated switches for shape memory performances, while allophanate network provided the permanent crosslinks for these PUs. The reversible DA bonds were obtained by the reaction of diisocyanate ended prepolymers with furfurylamine (FA) followed by the addition of bismaleimide (BMI) The permanent crosslinks between the linear chains containing DA bonds were achieved using additional amounts of diisocyanates (MDI or HDI) The above reaction path was supported by infrared spectroscopic results and swelling experiments. Tensile mechanical and shape memory properties in tension of the PUs were determined and discussed as a function of composition and crosslink densities deduced from swelling and dynamic mechanical analysis. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44145.