Hao Zeng
C&EN Article Assignment 10
Title of C&EN Article: Heat unzips polymethacrylates. Catalyst-free
depolymerization method could make these materials more affordable
Author: Bethany Halford (March 19, 2022)
Reference from original journal article: Hyun Suk Wang, Nghia P. Truong,
Zhipeng Pei, Michelle L. Coote, and Athina Anastasaki; “Reversing RAFT
Polymerization: Near-Quantitative Monomer Generation Via a Catalyst-Free
Depolymerization Approach”. (J. Am. Chem. Soc. 2022, DOI:
10.1021/jacs.2c00963).
Summary and Analysis:
Bethany Halford reported to C&EN news (March 19, 2022) on a catalyst free
method to regenerate monomers from reversible addition−fragmentation chain
transfer (RAFT) polymerization process. This new approach might help industrial
application of controlled radical polymerization (CRP), a polymer-building
reaction which is popular in research but not attractive to industry because of the
high cost. The new depolymerization process returns polymethacrylates to their
starting monomers with up to 92% conversion. These monomers could be repolymerized to the original polymer or other materials with different properties.
This research was led by Athina Anastasaki, a polymer materials professor at
the Swiss Federal Institute of Technology (ETH) in Zurich. Specifically, chemists
in Anastasaki’s lab unzipped the polymethacrylate by making a dilute solution of
the polymer in dioxane and heating it to 120 °C, in the presence a dithiobenzoate
RAFT agent. In doing so, the high end-group functionality of RAFT polymers
generate chain-end radicals, which subsequently trigger a rapid unzipping of both
conventional (e.g., poly(methyl methacrylate)) and bulky (e.g., poly(oligo(ethylene glycol) methyl ether methacrylate)) polymers. The depolymerization
and monomer production was analyzed by 1H NMR to demonstrate the
appropriate chemical shifts. The monomers generated can then be utilized to
reconstruct the linear polymer or create an entirely new insoluble gel that can
also be depolymerized. By regenerating both the monomers and the RAFT agent
to reduce the cost, researchers hope to make the RAFT polymerization
procedure, which has the advantage of precise monitoring product molecular
weights, more appealing to industry.
This work expands the potential of polymers made by controlled radical
polymerization (CRP), pushes the boundaries of depolymerization, offers
intriguing mechanistic aspects, and enables new applications in industry. The
new method is believed to be better than conventional recycling because after
the heat unzip, the products can be utilized for multiple processes including both
repolymerization and depolymerization. By using a flow system that could recycle
the solvent, the environmental concern of dioxane usage can also be addressed.