Chemically Recyclable Poly(1,3-dioxolane) with High Molecular Weight Achieved Using a Fluorinated Strategy of Organocatalyst

Abstract

The circular economy has emerged as a pivotal and irreversible future direction for the sustainable development of the global plastics industry, aiming to alleviate the severe environmental pollution and resource waste caused by traditional non-degradable plastics. Chemical recycling to monomers (CRM) converts waste polymers directly back to monomers, offering a highly promising approach to enabling a circular plastics economy. Poly(1,3-dioxolane) (PDXL) is an ideal thermoplastic for CRM owing to its excellent chemical recoverability, outstanding thermal resistance, and robust mechanical properties, making it a competitive alternative to commercial petroleum-based polyolefin plastics. In this work, high-efficiency ring-opening polymerization of 1,3-dioxolane (DXL) to prepare PDXL was successfully achieved in high activity using perfluorinated triphenylborane (B(C₆F₅)₃), while the unfluorinated analogue triphenylborane (BPh₃) is inert to the polymerization of DXL under identical reaction conditions. The as-prepared PDXL features a high number-average molecular weight of 178 kDa at a monomer-to-catalyst ratio ([DXL]/[B(C₆F₅)₃]) of 700 : 1, excellent thermal stability with 5% thermal decomposition temperature of 356 °C, and superior tensile strength (σ_B = 30 MPa), which far exceeds that of conventional commercial polyethylene materials. Significantly, the key active species involved in the polymerization process was isolated for the first time via equimolar reaction of B(C₆F₅)₃ with DXL, and thoroughly characterized by nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray diffraction analysis. Based on the crystal structure of active species, the detailed mechanism of the ring-opening polymerization of DXL has been proposed and confirmed through density functional theory (DFT) simulations. Furthermore, chemical recyclability of PDXL was accomplished using phosphotungstic acid (PTA) as a catalyst, yielding high-purity DXL monomer with high conversion, even in the presence of pigment additives or mixed plastic waste. PTA can be recovered and reused repeatedly for the depolymerization process. This work offers a feasible and efficient strategy for metal-free catalyst-mediated preparation of chemically recyclable polymers, promoting the advancement of circular plastics.

Keywords

Chemical recycling / Poly(1,3-dioxolane) / Metal-free catalyst / Fluorinated strategy / Organoboron catalyst / Cationic ring-opening polymerization / High molecular weight / Polymerization mechanism

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