# A Chemocatalytic Route to Stereoregular Poly(3-hydroxyhexanoate) and Its Statistical and Tri-Block Copolymers

## TL;DR

Scientists developed a new chemical method to create a type of biodegradable plastic with specific structures and properties, which could be useful for various applications.

## Contribution

A chemocatalytic route is introduced for synthesizing stereoregular P3HHx and its copolymers with tunable properties.

## Key findings

- P3HBHx can be produced rapidly in high yield with high molar mass and excellent mechanical properties.
- The tri-block copolymer P3HB-b-P3HHx-b-P3HB has a unique combination of low Tg and high Tm, expanding its application temperature range.
- The chemocatalytic method allows for precise control over PHA structure and performance.

## Abstract

Poly­(3-hydroxyhexanoate) (P3HHx)-based poly­(3-hydroxyalkanoate)­s
(PHAs) are biologically produced, commercially implemented PHAs, but
little is known in the open literature about the structure and property
characterizations of discrete, authentic homopolymer P3HHx, and its
copolymers with poly­(3-hydroxybutyrate) (P3HB). Here, we introduce
a chemocatalytic route to stereoregular (both isotactic and syndiotactic)
P3HHx and PHA copolymers with P3HB, including statistical copolymer
P3HBHx with various levels of 3HHx incorporation and discrete hard–soft–hard
triblock copolymer P3HB-b-P3HHx-b-P3HB, and present extensive characterizations of their structures,
thermal properties, and mechanical performance. The synthesis is efficiently
achieved by one-pot polymerization of eight-membered di­(n-propyl) and dimethyl (for copolymerization) diolides catalyzed by
chiral molecular catalysts. Notably, P3HBHx can be rapidly produced
in quantitative yield and exhibits high molar mass (M
n up to 551 kg/mol) as well as both high modulus (up to
1.39 GPa) and ductility (up to 445%), while P3HB-b-P3HHx-b-P3HB further extends application temperature
windows by possessing a unique combination of low T
g (−18 °C) and high T
m (154 °C) values. These findings highlight the stereomicrostructural
and architectural versatility of chemocatalytic routes to PHAs, which,
in turn, can be utilized to largely tune the PHA thermal properties
and mechanical performance.