Long-Chain Polyorthoesters as Degradable Polyethylene Mimics.

Tobias Haider,Oleksandr Shyshov,Oksana Suraeva,Frederik R Wurm,Ingo Lieberwirth,Max Von Delius

doi:10.1021/acs.macromol.9b00180

Tobias Haider, Oleksandr Shyshov + Show 4 more

Open Access

https://doi.org/10.1021/acs.macromol.9b00180

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Abstract

The persistence of commodity polymers makes the research for degradable alternatives with similar properties necessary. Degradable polyethylene mimics containing orthoester groups were synthesized by olefin metathesis polymerization for the first time. Ring-opening metathesis copolymerization (ROMP) of 1,5-cyclooctadiene with four different cyclic orthoester monomers gave linear copolymers with molecular weights up to 38000 g mol–1. Hydrogenation of such copolymers produced semicrystalline polyethylene-like materials, which were only soluble in hot organic solvents. The crystallinity and melting points of the materials were controlled by the orthoester content of the copolymers. The polymers crystallized similar to polyethylene, but the relatively bulky orthoester groups were expelled from the crystal lattice. The lamellar thickness of the crystals was dependent on the amount of the orthoester groups. In addition, the orthoester substituents influenced the hydrolysis rate of the polymers in solution. Additionally, we were able to prove that non-hydrogenated copolymers with a high orthoester content were biodegraded by microorganisms from activated sludge from a local sewage plant. In general, all copolymers hydrolyzed under ambient conditions over a period of several months. This study represents the first report of hydrolysis-labile and potentially biodegradable PE mimics based on orthoester linkages. These materials may find use in applications that require the relatively rapid release of cargo, e.g., in biomedicine or nanomaterials.

Highlights

Today polyethylene (PE) is the most used commodity polymer in the world.1 Because of its excellent mechanical properties, PE is used for a variety of applications.2 there are environmental issues related to the low degradability of PE in the environment
Moisture had to be strictly excluded during these procedures, as it would lead to hydrolysis of the orthoester
We report the synthesis of polyorthoesters by ring-opening metathesis polymerization (ROMP)

Summary

Introduction

Today polyethylene (PE) is the most used commodity polymer in the world. Because of its excellent mechanical properties, PE is used for a variety of applications. there are environmental issues related to the low degradability of PE in the environment. To mimic the properties of polyethylene while potentially enabling degradation at the same time, one approach lies in the incorporation of functional groups in long aliphatic polymer chains.. There, the functional groups act as “defects” in the polymer chains of the semicrystalline materials. Depending on their size, the defects are either part of the lamellar PE crystals (small defect size) or forced into the amorphous phase (bulky defects).. An increasing number of methylene units between the functional groups enhances van der Waals interactions between the polymer chains, leading to a higher degree of crystallinity.. Concerning degradability, long-chain polyesters, for example, did not show relevant enzymatic or hydrolytic degradation as water is hindered from penetrating into the materials due to the high crystallinity and hydrophobicity.. Similar to acetals in molecular structure, but with a higher hydrolysis rate and steric bulk, orthoesters can be a suitable alternative to synthesize acid-sensitive polymers

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