Synthesis, dynamic mechanical, and solid-state NMR spectroscopy of crown-ether-based linear aliphatic polyurethane rotaxanes

Linear aliphatic polyurethanes were synthesized from hexamethylene diisocya nate (HDI) and either ethylene glycol (EG) or diethylene glycol (DEG). Poly merization of HDI and EG in a 30-crown-10 (30c10) solvent afforded poly [(e thylene hexamethylenediurethane)n-rotaxa-(30-crown-10)(x)] with x/n = 0.02 (4% by mass). Polymerization of HDI and DEG in a 36-crown-12 (36c12) solven t provided poly[(oxydiethylene hexamethylenediurethane)(n)-rotaxa-(36-crown -12)(x)] with x/n = 0.15 (23% by mass). For both polyurethane-rotaxanes, th e melting temperatures are lower than those of the unthreaded backbones, an d the glass temperature decreases when the threading efficiency is sufficie ntly high. The dynamic mechanical (DM) spectrum of the EG-30c10-containing polyrotaxane is identical to that of its unthreaded backbone. For both EG-b ased polymers, vacuum drying led to the disappearance of a sub-T-g mechanic al loss around -85 degrees C (1 Hz). The DM spectrum of the DEG-36c12-conta ining polyrotaxane contains additional loss peaks in its tan delta versus t emperature curves, as compared to its unthreaded backbone. Solid-state 2D W ISE NMR revealed the new sub-T-g loss process around -53 degrees C to be du e to the onset of 36-crown-12 mobility in the polyrotaxane.