Solvent-Free PMMA Recycling to MMA at ~200 °C: ETH Zurich

Acrylic back to monomer at around 200 °C, without solvent: ETH Zurich simplifies PMMA recycling

04-Nov-26

ETH Zurich researchers have found that a small dose of one commercially available additive lets PMMA (acrylic glass) unzip back to its monomer, MMA, at about 200–230 °C. The process uses no solvent and works on coloured commercial Plexiglas. That is roughly half the temperature of conventional pyrolysis.

PMMA, sold under names such as Plexiglas and Perspex, is used for signage, display and lighting panels, automotive lamp covers, glazing, sanitary ware and medical devices. Global production is around 3.9 million tonnes a year. PMMA is one of the few plastics that can, in principle, be turned back into its own monomer. In practice, the industrial route is pyrolysis at roughly 400 °C and above. Pyrolysis uses a lot of energy, and the recovered MMA can carry up to about 3% impurities, which then hurt the quality of new polymer made from it.

The new work comes from the Laboratory of Polymeric Materials at ETH Zurich, led by Prof. Athina Anastasaki, with ETH colleagues Prof. Tae-Lim Choi and Prof. Gunnar Jeschke. Lead author is Richard Whitfield. The results are published in the peer-reviewed journal Nature Chemistry.

One additive, no solvent

The key is a class of compounds called N-hydroxyimides, related to N-hydroxyphthalimide (NHPI). The best performer was N-hydroxytetrachlorophthalimide (TCNHPI). It is mixed with the solid polymer in small amounts: 5 mol% per repeat unit at first, and the team later cut this to 0.4 mol% without losing yield. No solvent is involved; the polymer is simply heated with the additive and the MMA distils off.

An earlier light-driven method from the same group needed the polymer to be dissolved in a chlorinated solvent. Removing the solvent makes the new route much closer to what a recycler could run in standard equipment.

How it works

When heated, the additive forms reactive radicals. These pull a hydrogen atom off the PMMA backbone. The damaged chain then breaks in the middle, and the new chain end "unzips", releasing MMA molecules one after another. Over the run the polymer's molecular weight falls from about 700 kDa to about 20 kDa as it is consumed.

Key results (lab scale)

Parameter	Result reported
Onset of depolymerisation	about 175–180 °C
Mass loss in 2 h	86% at 200 °C, 88% at 210 °C, 91% at 220 °C
Preparative run	5.1 g blue Plexiglas → 4.6 g MMA (90% yield), 4 h at 230 °C
Monomer quality	colourless, high-purity MMA by NMR
Additive level	0.05 equiv. reduced to 0.004 equiv. with no yield loss
Pyrolysis benchmark	usually above 400 °C, up to ~3% impurities

Other findings:

Commercial Plexiglas in various colours depolymerised to up to 90% conversion, despite containing co-monomers, plasticisers, dyes and inhibitors.
Aluminium hydroxide-filled PMMA (10–50 wt% Al(OH)3) reached about 70% depolymerisation at 180 °C, similar to unfilled material.
A non-chlorinated version of the additive (a dimeric N-hydroxyimide) also gave more than 90% monomer recovery.
ETH's release quotes monomer yields as high as 98% and says the recovered MMA can make new polymer of the same quality as virgin material.

Limitations

The researchers note several open points:

All work is at laboratory scale; the largest run was about 5 g. Scale-up has not yet been tested.
Lower-molecular-weight PMMA gave lower yields (66% for a 25 kDa polymer, rising to 87% with more additive).
The method works for polymethacrylates only. Polyacrylates were broken down but did not give back monomer.
The best-performing additive is chlorinated, and the team wants to understand the mechanism further and find faster, higher-yield reagents.

ETH Zurich has filed a patent application and is seeking licensees. The group plans to test the same principle on polystyrene.

Source

Based on the ETH Zurich news release as reported by AZoM (20 October 2026) and Innovation News Network (19 October 2026), and on the paper itself. Original paper: R. Whitfield, V. Lohmann, M. Agrachev, H. Kim, H. S. Wang, N. De Alwis Watuthanthrige, N. P. Truong, T.-L. Choi, G. Jeschke and A. Anastasaki, "Lower-temperature bulk depolymerization of commercial polymethacrylates", Nature Chemistry (2026), DOI: 10.1038/s41557-026-02232-4. Open-access manuscript: ETH Research Collection.