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.

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.

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