# Structural Properties of Coniferyl Alcohol-Based Low Transition Temperature Mixtures

## TL;DR

This paper explores the structural properties of mixtures made from coniferyl alcohol and choline chloride, revealing how their molecular organization changes with temperature.

## Contribution

The study is the first to investigate lignin-derived monomers in low transition temperature mixtures (LTTMs).

## Key findings

- LTTMs with coniferyl alcohol and choline chloride have glass transition temperatures of −24.6 and −16.8 °C with no melting points.
- The mixtures are heterogeneous, showing two regions of molecular mobility between 20 and 90 °C.
- Strong hydrogen bonding involving the γ-OH group stabilizes the restricted molecular mobility region.

## Abstract

This study examines the structural organization of low
transition
temperature mixtures (LTTMs) based on coniferyl alcohol, a primary
monolignol, at the macroscopic and microscopic levels. The work presents
the first investigation into the use of lignin-derived monomers as
constituents of LTTMs. The LTTMs prepared with 2:1 and 3:1 molar ratios
of coniferyl alcohol to choline chloride exhibited glass transition
temperatures (T
g) of −24.6 and
−16.8 °C, respectively, and with no observable melting
points (T
m). The respective water contents
were 0.4790 and 0.7564 wt %, similar to that reported for other natural
deep eutectic solvents. Time–domain nuclear magnetic resonance
analysis revealed that these LTTMs are heterogeneous and exhibited
two regions between 20 and 90 °C due to differences in molecular
mobility. Furthermore, Fourier-transform infrared spectroscopy and
proton NMR demonstrated that the region of restricted molecular mobility
was stabilized by strong hydrogen bonding, mainly involving the γ-OH
group of the coniferyl alcohol. The weak hydrogen bonds were gradually
broken with an increase in temperature, leading to structural reorganization.
As the temperature increased, the system transitioned to a state in
which the hydrogen-bonded clusters and more freely dispersed molecular
regions were present in approximately equal proportions.