Polymer grafting onto polyurethane backbone via Diels-Alder reaction

The aliphatic polyurethane with pendant anthracene moieties (PU-anthracene) was prepared from polycondensation of anthracen-9-yl methyl 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoate (anthracene diol), 1 with hexamethylenediisocyanate in the presence of dibutyltindilaurate in CH₂Cl₂ at room temperature for 10 days. Thereafter, the PU-anthracene (M_n,GPC = 12,900 g/mol, M_w/M_n = 1.87, relative to PS standards) was clicked with a linear α-furan protected-maleimide terminated-poly(methyl methacrylate) (PMMA-MI) (M_n,GPC = 2500 g/mol, M_w/M_n = 1.33), or -poly(ethylene glycol) (PEG-MI) (M_n,GPC = 550 g/mol, M_w/M_n = 1.09), to result in well-defined PU-graft copolymers, PU-g-PMMA (M_n,GPC = 23800 g/mol, M_w/M_n = 1.65, relative to PS standards) or PU-g-PEG (M_n,GPC = 11,600 g/mol, M_w/M_n = 1.45, relative to PS standards) using Diels-Alder reaction in dioxane/toluene at 105 °C. The Diels-Alder grafting efficiencies were found to be over 93-99% using UV spectroscopy. Moreover, the structural analyses and the thermal transitions of all copolymers were determined via ¹H NMR and DSC, respectively.