# Effects of Isohexide Stereochemistry on Vinylogous Urethane Covalent Adaptable Networks

## TL;DR

This paper explores how the stereochemistry of isohexides affects the properties of covalent adaptable networks made from starch, enabling tailored mechanical and thermal performance.

## Contribution

The study introduces a method to tailor CAN properties using isohexide stereochemistry and vinylogous urethane chemistry.

## Key findings

- Tensile strengths ranged from 1.57 to 19.1 MPa depending on isohexide isomer and amine structure.
- Glass transition temperatures varied from 20 to 114 °C, and thermal stabilities from 200 to 305 °C.
- Mechanical reprocessing was demonstrated without performance decay after two cycles.

## Abstract

The starch-derived isohexides, with their unique structures
of
two fused tetrahydrofuran rings in a cis conformation,
have been exploited to prepare covalent adaptable networks (CANs)
and to tailor and understand their structure–property relationships,
in pursuit of replacing oil-based thermosets. Here, dynamicity was
achieved through vinylogous urethane chemistry, rigidity via the use
of the starch-derived isomeric building blocks isosorbide, isomannide,
and isoidide, and flexibility through the amines utilized. Similar
to what is known for thermoplastics, depending on the isomer chosen,
thermal stability and mechanical properties could be tailored to some
extent. The distance between cross-links was ruled by the amines employed,
and when this distance was long enough to allow sufficient chain mobility,
stereochemical effects on mechanical performance were observed. The
CAN structures all display thermoset properties, and as a consequence
of the incorporated dynamic bonds, they were mechanically reprocessable.
Based on the CANs structural design, i.e., isohexide isomer and amine
structure, tensile strengths (σb) ranging from 1.57
to 19.1 MPa, glass transition temperatures (T
g) ranging from 20 to 114 °C, and thermal stabilities
(T
d,5%) between 200 and 305 °C were
achievable. Mechanical reprocessing was proven, and no mechanical
performance decay was observed after two reprocessing cycles. This
provides important information on the structure–property relationship
of CANs from starch-derived building blocks, and consequently, how
material properties can be tailored depending on the targeted application.