Self-immolative
polymers (SIPs) are promising members of the emerging
class of recyclable polymers with the ability to end-to-end depolymerize
to their monomers. Unfortunately, SIPs are often synthesized by cumbersome
procedures at low temperatures in protected atmosphere. In this study,
a SIP with a novel poly(disulfide) backbone is introduced, using dl-dithiothreitol (DTT) as the monomer. Remarkably, poly(DTT)
can be produced by solid-state polymerization in a robust and easily
scalable process by mechanically mixing DTT with 2,2′-dithiodipyridine
as the end-capping agent. The new polymer possesses good thermal and
chemical stabilities, but once its depolymerization is triggered,
this proceeds smoothly within minutes to afford cyclic DTT because
of a favorable intramolecular back-biting thiol–disulfide exchange
reaction in the polymer backbone. As a proof of concept, the cyclic
DTT waste was recovered, reduced to DTT monomer, and repolymerized
in a closed-loop approach.
Fibre-reinforced epoxy composites are well established in regard to load-bearing applications in the aerospace, automotive and wind power industries, owing to their light weight and high durability. These composites are based on thermoset resins embedding glass or carbon fibres1. In lieu of viable recycling strategies, end-of-use composite-based structures such as wind turbine blades are commonly landfilled1–4. Because of the negative environmental impact of plastic waste5,6, the need for circular economies of plastics has become more pressing7,8. However, recycling thermoset plastics is no trivial matter1–4. Here we report a transition-metal-catalysed protocol for recovery of the polymer building block bisphenol A and intact fibres from epoxy composites. A Ru-catalysed, dehydrogenation/bond, cleavage/reduction cascade disconnects the C(alkyl)–O bonds of the most common linkages of the polymer. We showcase the application of this methodology to relevant unmodified amine-cured epoxy resins as well as commercial composites, including the shell of a wind turbine blade. Our results demonstrate that chemical recycling approaches for thermoset epoxy resins and composites are achievable.
Functional materials engineered to degrade upon triggering are in high demand due their potentially lower impact on the environment as well as their use in sensing and in medical applications. Here, stimuli‐responsive polymers are prepared by decorating a self‐immolative poly(dithiothreitol) backbone with pendant catechol units. The highly functional polymer is fashioned into stimuli‐responsive gels, formed through pH‐dependent catecholato–metal ion cross‐links. The gels degrade in response to specific environmental changes, either by addressing the pH responsive, non‐covalent, catecholato–metal complexes, or by addition of a thiol. The latter stimulus triggers end‐to‐end depolymerization of the entire self‐immolative backbone through end‐cap replacement via thiol–disufide exchanges. Gel degradation is visualized by release of a dye from the supramolecular gel as it itself is converted into smaller molecules.
Self-immolative polymers (SIPs) are a class of degradable stimuli-responsive polymers, which, upon removal of labile end-caps, depolymerize selectively and stepwise to small molecules.
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