Remarkable diastereomeric effect on thermoresponsive behavior of polyurethane based on lysine and tartrate ester derivatives

Abstract

This study describes the long-distance diastereomeric effect on thermoresponsive properties in water-soluble diastereomeric polyurethanes (PUs) composed of an L-lysine ethyl ester diisocyanate and a trimethylene glycol L-/D-tartrate ester, which have differences in spatial arrangements of the ethyl esters in the mirror image. The PUs based on L-lysine and L-/D-tartrate ester, named L-PU and D-PU, were synthesized with various number average molecular weights from 4700 to 13 100. In turbidimetry, L-PU showed a steep phase transition from 100%T to 0%T within about 10 °C at 4 g L⁻¹, whereas D-PU did not change completely to 0%T transmittance even at 80 °C at 4 g L⁻¹. In addition, the thermoresponsive properties of L-PU were less affected by concentration than those of D-PU. This long-distance diastereomeric effect on thermoresponsive behavior between L-PU and D-PU appeared in common among 6 samples with 4700 to 13 100 number average molecular weight. In the dynamic light scattering experiments at each transmittance, the hydrodynamic diameter (D_h) of l-PU increased up to 1000 nm, while the D_h of D-PU remained almost at 200–300 nm. The CO stretching vibration of FT-IR spectra showed that D-PU has more hydrogen-bonded ester groups than L-PU. Thus, we speculated that the difference in the retention of polymer chains in the micelle to promote intermicellar bridging generates the long-distance diastereomeric effect.