Aliphatic Long-Chain Polypyrophosphates as Biodegradable Polyethylene Mimics

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.

The Chemical Recycling of Polyesters for a Circular Plastics Economy: Challenges and Emerging Opportunities

“…Examples include polyphosphonates [309] and polyesters [310] among others. [311] Recently, Wurm and co‐workers reported long‐chain polyorthoesters [312] and polypyrophosphates [313] as degradable alternatives to PE. Post polymerisation hydrogenation of the polyorthoesters yielded hard, solid materials with thermal properties similar to PE.…”

Noncovalent Hydrogen Bonds Tune the Mechanical Properties of Phosphoester Polyethylene Mimics

“…Such polyphosphoesters (PPEs) or polypyrophosphates crystallized similar to polyethylene but bring the potential to be degradable. 18−20 In linear main-chain PPEs, two phosphoesters build the polymer backbone, whereas the pendant ester group can be used to tune their chemical functionality. 21,22 Besides chemical functionality, herein we used the pendant chain to introduce physical cross-linking into a polyphosphoester PE mimic.…”

RNA-inspired intramolecular transesterification accelerates the hydrolysis of polyethylene-like polyphosphoesters

“…35%. This value is significantly higher in comparison to an ADMET pyrophosphate with the same aliphatic spacer of 20 CH 2 groups (23%), 21 but lower than for comparable long-chain polyesters like e.g. poly(pentadecalactone) with a crystallinity of 64%.…”

“…A polyphosphate with an ethoxy side chain and an aliphatic spacer of 20 CH 2 groups did not show any degradation in phosphate-buffered saline (PBS) solution (pH 7.1) at 37 °C for 2 months. 21 Only at pH > 12 the polymer was degradable within this timeframe. Other PE-mimics like long-chain polyesters showed similar degradation profiles: poly(pentadecalactone) was stable at pH 7.2 for 2 years and showed no decrease in molecular weight.…”

“…In contrast to water-soluble polymers, polyethylene-like PPEs are in general remarkably robust to hydrolytic degradation due to increased crystallinity and hydrophobicity. A polyphosphate with an ethoxy side chain and an aliphatic spacer of 20 CH 2 groups did not show any degradation in phosphate-buffered saline (PBS) solution (pH 7.1) at 37 °C for 2 months 21. Only at pH >12 thePage 13 of 30 Chemical Science Chemical Science Accepted Manuscript Open Access Article.…”