The Impact of Polymer Dispersity and Monomer Sequence on Self-healing and Photodegradation of Dynamically Crosslinked Polymers

Project Information

DISCOSH

Grant agreement ID: 101030516

DOI

10.3030/101030516

Project closed

EC signature date 22 April 2021

Start date 15 January 2022

End date 14 January 2024

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 191 149,44

EU contribution

€ 191 149,44

Coordinated by

EIDGENOESSISCHE TECHNISCHE HOCHSCHULE ZUERICH
Switzerland

Periodic Reporting for period 1 - DISCOSH (The Impact of Polymer Dispersity and Monomer Sequence on Self-healing and Photodegradation of Dynamically Crosslinked Polymers)

Reporting period: 2022-01-15 to 2024-01-14

Summary of the context and overall objectives of the project

The demand for plastic continues to surge in society, contributing to a pressing environmental issue. The disposal of polymers and plastics poses a substantial challenge as they exhibit persistent characteristics in the environment, lasting for years. Recognizing the escalating threat of pollution due to prolonged polymer persistence, there has been a increased focus on exploring degradation methods. Traditionally, the degradation of polymers often results in the formation of smaller fragments that still find their way into soil, water, or air.

In our project, we took a progressive approach to minimize the persistence of polymers in the environment by employing depolymerization methods. This innovative technique allows us to break down long-chain polymers into their original monomer units, presenting an opportunity to recycle and create new polymer materials from existing ones. By moving beyond conventional degradation methods, we aim to contribute to a more sustainable and environmentally friendly approach to managing polymer waste. The reproduced monomers can be effectively used in resynthesis of polymeric materials by reducing the waste.

Controlled radical polymerization (CRP) is a polymerization technique that can yield well-defined polymers with predictable molecular weights, various architectures, and tunable molar mass distributions. Among the CRP strategies developed so far, reversible addition–fragmentation chain-transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) are considered the most versatile and widely utilized methods. Despite the numerous benefits of these techniques in polymer synthesis, studies on the depolymerization of these polymers are still in the preliminary stages. The project's primary objective was to tackle the existing challenge of depolymerizing polymers synthesized by the controlled radical polymerization (CRP) method at lower temperatures, while also addressing the issue of depolymerizing longer polymer chains.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Within this project, our primary focus was on achieving low-temperature depolymerization of RAFT polymers by altering the electronic properties of the RAFT agents and achieving higher depolymerization conversions with longer polymer chains. The latter was accomplished through the preparation of bifunctional polymers.

In WP1, we synthesized RAFT agents with various substitutions to control their activities. The enhancement of electron density of these RAFT agents enabled the polymers to depolymerize at lower temperatures (90 °C) than reported in the literature (120 °C). Five different substitutions were employed to study both the enhancement and decrement effects on depolymerization. Polymers containing the RAFT agent with the lowest electron density exhibited a slower depolymerization at lower temperatures and a lower yield (~20%) of depolymerization. Conversely, the enhancement of electron density of the RAFT agent facilitated a higher rate of depolymerization, with yields closer to 80%. These substitutions highlight the fact that depolymerization can be facilitated without using any catalyst by simply altering the electron densities of the RAFT agents. Furthermore, calculations demonstrated that the enhanced electron density of the RAFT agents facilitated faster C-S bond scission between the RAFT agent and the polymer, ultimately resulting in faster and higher yield depolymerization. To date, the project results have been shared in conferences, and the main manuscript is nearing completion for publication.

In WP2, our aim was to address the enhancement of depolymerization yields in RAFT polymers and introduce the depolymerization of bifunctional polymers. Bifunctional polymers, as described in literature, have been utilized in various applications such as material preparation and polymer self-assembly. This research underscores the importance of having multiple RAFT active sites in RAFT polymers and the use of different bifunctional RAFT agents to achieve higher depolymerization yields. Within this work package, we synthesized two different bifunctional RAFT agents with active sites located at the ends and in the middle of the chains. Having multiple active sites facilitated multiple activations of the depolymerization process, thus enhancing depolymerization yields. Furthermore, we highlighted that the positioning of the RAFT agent (whether at the end or in the middle) also affects the final conversion of the depolymerization. Having RAFT agents in the middle of the polymer chains further enhances depolymerization and yields better monomer recovery at the end of the depolymerization process. Moreover, we delved into the mechanisms of depolymerization of these polymers and analyzed the depolymerization processes of bifunctional polymers in detail. The outcomes of this project are currently undergoing preparation for publication, and we anticipate their publication in the near future.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

This project focuses on enhancing the depolymerization process of polymers synthesized using the RAFT (Reversible Addition-Fragmentation chain Transfer) polymerization technique. By optimizing the depolymerization conditions to operate at lower temperatures compared to those reported in existing literature, this initiative aims for efficient breakdown of longer polymer chains. The resultant regenerated monomers can then be reintegrated into the synthesis of new polymer materials, effectively closing the loop on material use and waste.

This advancement in depolymerization holds substantial societal benefits across multiple fronts. Foremost, it addresses the pressing issue of plastic and polymer pollution by offering a more streamlined and effective means of breaking down these materials. As the demand for polymers continues to surge, the disposal of used polymeric products becomes increasingly challenging. Historically, such materials were often discarded in landfills. However, due to their persistent nature in the environment, it became evident that a chemical breakdown was necessary to mitigate their long-lasting impact. Existing methods for depolymerizing polymers into their constituent monomeric units typically require substantial energy inputs.

Polymer synthesis using CRP (Controlled Radical Polymerization) techniques not only enables the creation of well-defined polymers with diverse architectures but also incorporates active end groups that reduce the energy requirements for subsequent depolymerization. Consequently, this approach to depolymerizing RAFT polymers facilitates monomer regeneration at lower temperatures, thereby promoting a low-energy depolymerization process that saves costs. Beyond its immediate applications, this advancement contributes to the broader goals of waste reduction and resource conservation. By minimizing the accumulation of persistent waste in the environment and fostering the regeneration of monomers, this initiative promotes a more sustainable circular economy model.

Description of overall project objectives