Ultratough Thermoplastic Elastomers Based on Chemically Recyclable Cycloalkyl-Substituted Polyhydroxyalkanoates

Area of Science:

• Polymer Chemistry
• Sustainable Materials
• Chemical Recycling

Background:

• Chemical recycling of polyhydroxyalkanoates (PHAs) to propiolactone monomers faces challenges due to high ring strain and side reactions.
• Developing efficient and sustainable routes for PHA monomer recovery is crucial for circular economy principles.

Purpose of the Study:

• To design a novel propiolactone monomer with enhanced reactivity for ring-opening polymerization and efficient depolymerization.
• To explore the potential of this new monomer in synthesizing high-performance thermoplastic elastomers (TPEs).

Main Methods:

• Design and synthesis of α-spiro-cyclohexyl-propiolactone (SHPL).
• Ring-opening polymerization of SHPL with low catalyst loading (<1 ppm).
• Depolymerization of the resulting poly(3-hydroxy-2-spiro-cyclohexylpropionate) (P3HSHP).
• One-pot copolymerization of SHPL with ε-caprolactone (CL) to create TPEs.

Main Results:

• SHPL exhibits high reactivity in ring-opening polymerization.
• P3HSHP demonstrates high thermal stability (Td = 364 °C, Tm = 272 °C) and can be depolymerized to SHPL in 86% yield without side products.
• Gradient copolymers of CL and SHPL (P(CL2000-grad-SHPL500)) show superior TPE properties: tensile strength (58.8 MPa), stretchability (1959%), toughness (600 MJ/m³), and elastic recovery (>90%).

Conclusions:

• The novel SHPL monomer overcomes challenges in propiolactone-based PHA recycling.
• SHPL facilitates the creation of high-performance, sustainable thermoplastic elastomers.
• This advancement supports the development of advanced materials for a circular economy.