Chain-End Controlled Depolymerization Selectivity in α,α-Disubstituted Propionate PHAs with Dual Closed-Loop...

Area of Science:

• Polymer Chemistry
• Materials Science
• Biomaterials

Background:

• Poly(3-hydroxyalkanoate)s (PHAs) are biodegradable polymers with diverse applications.
• C3 propionate PHAs, especially poly(3-hydroxy-2,2-dimethylpropionate) (P3H(Me)2P), are less studied than C4 butyrates.
• P3H(Me)2P offers high melting temperature and crystallinity but suffers from inefficient synthesis and brittleness.

Purpose of the Study:

• To develop simple and efficient synthetic routes for P3H(Me)2P.
• To achieve closed-loop recycling of P3H(Me)2P via step-growth polycondensation (SGP) and ring-opening polymerization (ROP).
• To create novel PHA copolymers with improved mechanical and barrier properties.

Main Methods:

• Step-growth polycondensation (SGP) of hydroxyacid or methyl ester to produce low-to-medium molar mass P3H(Me)2P.
• Base-catalyzed depolymerization of P3H(Me)2P to form lactones.
• Ring-opening polymerization (ROP) of lactones to yield high-molar-mass P3H(Me)2P.
• Hydrolysis and methanolysis for depolymerization and recycling.
• Copolymerization of P3H(Me)2P with other monomers.

Main Results:

• Efficient SGP and ROP routes established for P3H(Me)2P synthesis.
• Closed-loop recycling achieved with high yields for hydroxyacid (99%) and hydroxyester (91%).
• Chain end control influences lactone formation selectivity (4- or 12-membered).
• Copolymers P3H(Me/R)2P exhibit high tensile strength, ductility, and barrier properties.
• P3H(iPr)2P achieved a record-high melting temperature of 266 °C within the PHA family.

Conclusions:

• Novel synthetic and recycling strategies for P3H(Me)2P have been developed.
• Tailored PHA copolymers demonstrate significant improvements in mechanical and barrier performance.
• The study expands the potential applications of PHAs, particularly high-performance variants.