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

Daisuke Aoki,Akihiro Miyake,Hiroharu Ajiro,Wanpen Tachaboonyakiat

doi:10.1039/d1ra05877k

Daisuke Aoki, Akihiro Miyake + Show 2 more

Open Access

https://doi.org/10.1039/d1ra05877k

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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 (Dh) of l-PU increased up to 1000 nm, while the Dh of d-PU remained almost at 200–300 nm. The C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O 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.

Highlights

Thermoresponsive polymers have been developed in a wide range of molecular designs because of their potential application as smart materials.[1,2,3,4] Stereoregularity is a helpful molecular design strategy for controlling thermoresponsive properties using conformational entropy
We propose the long-distance diastereomeric effect on thermoresponsive behavior in polyurethane diastereomers consisting of an asymmetric L-lysine-based diisocyanate (LDI) and a symmetric diol OEG L-/D-tartrate ester bearing two chiral carbons
The previous PUs composed of hexamethylene diisocyanate (HDI) and OEG3TA were difficult to control polymerization, with a number average molecular weight (Mn) up to 6500 and a large Mw/Mn of about 4.21 We attributed this problem to OEG3TA impurity mixing a small amount of mOEG3 and a low reaction rate and addressed it by changing the eluent of column chromatography and extending the polymerization time

Summary

Introduction

Thermoresponsive polymers have been developed in a wide range of molecular designs because of their potential application as smart materials.[1,2,3,4] Stereoregularity is a helpful molecular design strategy for controlling thermoresponsive properties using conformational entropy. We propose the long-distance diastereomeric effect on thermoresponsive behavior in polyurethane diastereomers consisting of an asymmetric L-lysine-based diisocyanate (LDI) and a symmetric diol OEG L-/D-tartrate ester bearing two chiral carbons. This diastereomeric PU system is imagined as different spatial arrangements of ethyl esters in the mirror image, the actual difference in chirality is derived from tartrates (Fig. 1). The slight spatial difference of the long-range ethyl ester groups was ampli ed, leading to different thermoresponsive behavior in water media

Materials

Polymerization for L-PU and D-PU

Synthesis and characterization of diastereomeric PUs

Differential scanning calorimetry

Dynamic light scattering

Conclusions