Abstract
Biodegradable polyethylene mimics have been synthesized by the introduction of pyrophosphate groups into the polymer backbone, allowing not only hydrolysis of the backbone but also further degradation by microorganisms. Because of cost, low weight, and good mechanical properties, the use of polyolefins has increased significantly in the past decades and has created many challenges in terms of disposal and their environmental impact. The durability and resistance to degradation make polyethylene difficult or impossible for nature to assimilate, thus making the degradability of polyolefins an essential topic of research. The biodegradable polypyrophosphate was prepared via acyclic diene metathesis polymerization of a diene monomer. The monomer is accessible via a three-step synthesis, in which the pyrophosphate was formed in the last step by DCC coupling of two phosphoric acid derivatives. This is the first report of a pyrophosphate group localized in an organic polymer backbone. The polypyrophosphate was characterized in detail by NMR spectroscopy, size exclusion chromatography, FTIR spectroscopy, differential scanning calorimetry, and thermogravimetry. X-ray diffraction was used to compare the crystallization structure in comparison to analogous polyphosphates showing poly(ethylene)-like structures. In spite of their hydrophobicity and water insolubility, the pyrophosphate groups exhibited fast hydrolysis, resulting in polymer degradation when films were immersed in water. Additionally, the hydrolyzed fragments were further biodegraded by microorganisms, rendering these PE mimics potential candidates for fast release of hydrophobic cargo, for example, in drug delivery applications.
Highlights
Polyethylene (PE) is the most produced commodity polymer today.[1]
Biodegradable polyethylene mimics have been synthesized by the introduction of pyrophosphate groups into the polymer backbone, allowing hydrolysis of the backbone and further degradation by microorganisms
The biodegradable polypyrophosphate was prepared via acyclic diene metathesis polymerization of a diene monomer
Summary
Polyethylene (PE) is the most produced commodity polymer today.[1]. With the invention of Karl Ziegler in the past century,[2] perfectly linear PE was accessible that changed our everyday life drastically.[3]. Upon immersing polymer films in basic or acidic conditions, cleavage occurred selectively in anhydride groups, and the phosphoester bonds remained intact during the course of their study.[19] To date, no polypyrophosphates have been reported as degradable mimics for PE with a potentially very fast hydrolysis. Hydrogenation of the unsaturated product from the ADMET polycondensation was performed without any further catalyst addition by a modified Grubbs catalyst to produce the saturated PE mimic This is the first example of a PE mimic with very fast hydrolysis conditions of polymer films. The degradation time from the 31P NMR spectra for full hydrolysis of the pyrophosphate bonds was comparable to the full weight loss of the P1-H films. D2O and 0.05 mL of TFA or DIPEA. (f) Biodegradation of P1-H, P2-H, and starch in aqueous conditions with microorganisms from activated sludge
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