Description:
Recyclable Biopolymers from Chemical Ring-Opening Polymerization of Five-Membered Heterocyclic Monomers by Basic Catalysts
At a Glance:
The invention is the first effective organopolymerization of the biorenewable “non-polymerizable” gamma-butyrolactone (γ-BL) to high-molecular-weight metal-free recyclable polyester.
The chemical synthesis of PγBL, a highly useful biomaterial, offers a significant economical advantage because it is inexpensive to create.
Potential commercial applications are biomaterials, biomedical applications, biodegradable polyesters, and thermal recyclable plastics.
Background:
Organopolymerization utilizing small-molecule organic compounds as catalysts or initiators has enabled the synthesis of a broad range of polymers via various mechanistic pathways and grown into a preferred method when metal-free products or processes are of primary concern. A class of organic catalysts that attracted increasing attention in polymer synthesis is polyaminophosphazenes, which are uncharged, extremely strong organic bases with low nucleophilicity. In particular, the P4-phosphazene base, 1-tert-butyl-4,4,4-tris(dimethylainino)-2,2bis[tris(dimethylamino)phosphoranylid-enamino]-2λ5, 4λ5-catenadi(phosphazene) (‘Bu-P4), is one of the strongest known neutral bases with a pKa of 30.25 (DMSO) for its conjugate acid and the cation [‘Bu-P4H] being 1.4 nm in diameter. Utilizing its high Brønsted basicity, several effective metal-free initiator systems have been developed by combining ‘Bu-P4 with a co-initiator such as an enolizable organic acid (to generate enolate active species) and alcohol (to generate alkoxide active species); examples highlighted here include anionic polymerization of methyl methacrylate (MMA), ring-opening polymerization (ROP) of cyclosiloxanes and ethylene oxide, as well as stereoselective ROP of lactide by the related 1 -pyrene-butanol (PBNOL)/l-tert-butyl-2,2,4,4,4pentads(dimethylamino)-2λ5, 4λ5-catenadi(phosphazene) (‘Bu-P2) initiating system. ‘Bu-P4 has also been employed as an efficient catalyst for the well-controlled group-transfer polymerization of MMA and other functionalized methacrylates initiated by a silyl ketene acetal.
Technology Overview:
The bio-derived five-membered γ-butyrolactone (γ-BL), due to its low strain energy and this high thermodynamic stability, is commonly referred to as “non-polymerizable” by chemical ring-opening polymerization (ROP), a powerful synthetic methodology commonly employed for the chemical synthesis of biodegradable and biocompatible aliphatic polyesters from cyclic esters or lactones with relatively high strain energy. Chemical synthesis of poly(γ-butyrolactone) (PγBL) through the ROP process in appreciable yield has only been realized under high pressure (e.g., 20,000 atm at 160 oC), but producing only low-molecular-weight oligomers. This invention describes the first effective organopolymerization of the biorenewable γ-BL to high-molecular-weight metal-free recyclable polyester. The superbase tBu-P4 is found to directly initiate this polymerization through depronation of γ-BL to generate reactive enolate species. When combined with a suitable alcohol, the tBu-P4 based system rapidly converts γ-BL into polyesters with high monomer conversions (up to 90%), high molecular weights (Mn up to 26.7kg/mol), and complete recyclability (quantitative γ-BL recovery).
Benefits:
First effective organopolymerization of the bio-derived non-strained five-membered lactone γ-BL for the synthesis of high molecular weight, metal-free polyester Pγ-BL
Inexpensive to synthesize and economically advantageous
