Metal-Catalyzed Switching Degradation of Vinyl Polymers via Introduction of an “In-Chain” Carbon–Halogen Bond as the Trigger

Abstract

In this work, we achieved switching degradation of vinyl polymers made of a carbon–carbon bonded backbone. Crucial in this strategy was a small feed of methyl α-chloroacrylate (MCA) as the comonomer in radical polymerization of methyl methacrylate (MMA) so that the carbon–halogen bonds were introduced as the triggers for degradation. The “in-chain” trigger was activated by a one-electron redox metal catalyst as the chemical stimulus to generate the carbon-centered radical species, and subsequently, the neighboring carbon–carbon bond was cleaved via an electron transfer of the radical species giving the terminal olefin. Particularly, an iron complex (FeCl2) in conjunction with tributylamine (n-Bu3N) was effective as the chemical stimulus to allow the switching degradation, where the molecular weight was gradually decreased over time. The switching feature was confirmed by some control experiments.

Backbone Degradation of Polymethacrylates via Metal-Free Ambient-Temperature Photoinduced Single-Electron Transfer

“…In this work, we report on vinyl polymers preprogrammed for light-induced, ambient-temperature degradation via inclusion of SET-accepting phthalimide ester-containing repeat units. We find that methacrylate-based polymer backbones are susceptible to polymer degradation, as evidenced by a significant reduction in polymer molecular weight and in accordance with recent findings by Ouchi et al Low molar incorporation of redox-active NAP monomer units by copolymerization with methacrylates allowed for efficient degradation and molecular weight reduction for vinyl polymers with all-carbon backbones under very mild conditions (i.e., ambient temperature and green light). Furthermore, we were interested in investigating the potential degradation of acrylate- and styrene-based polymers.…”

“…This stability ultimately contributes to the modern challenge of achieving closed-loop plastic recycling, as polymer materials often retain robustness long after their intended usage lifetime. − Degradation experienced by these vinyl polymers ultimately hinges on molecular weight reduction via backbone fission events facilitated by exogenous, high-energy stimuli (e.g., UV light and high temperature). − Current strategies to produce degradable vinyl polymers include radical ring-opening polymerization of cyclic ketene acetals, which reduces backbone inertness via inclusion of hydrolyzable ester linkages. , Beyond this notable exception, backbone cleavage of radical-derived chain-growth polymers is typically limited to fairly severe degradation conditions via free radical mechanisms. A common theme in polymer degradation is radical formation on the polymer backbone followed by bond breaking via β-scission. − Indeed, recent reports by Ouchi et al outline both partial polymer unzipping and poly­(methacrylate) degradation via backbone radical generation using transition metal catalysts at elevated temperatures. , …”

“…10−12 Indeed, recent reports by Ouchi et al outline both partial polymer unzipping and poly-(methacrylate) degradation via backbone radical generation using transition metal catalysts at elevated temperatures. 13,14 There have recently been numerous examples of decarboxylative radical cross-coupling small-molecule reactions utilizing N-(acyloxy)phthalimide derivatives as single-electron transfer (SET) acceptors. 15−19 Applying this class of transformation to polymer-based systems seems to be a promising and somewhat untapped avenue to expand the field of post-polymerization modification.…”

“…In this case the product of the reaction was large enough to assess on GPC. By comparing the M p,fobs of the polymer to the M p , ftheo assuming 100% of NAP monomer units would produce a scission event, the degradation efficiency (E deg ) 13 was calculated to be 86% (Table 1, equations in SI). The molar-mass dispersity increase following degradation is attributed to the statistical incorporation of PhthMA monomer units.…”

Photocatalytic Direct Decarboxylation of Carboxylic Acids to Derivatize or Degrade Polymers

“…[28,29] Additionally, comonomers that can generate carbon-centered radicals and subsequently lead to cleavage of adjacent CÀ C bonds may be integrated in poly(meth)acrylate backbones to achieve degradation. [12,30] We demonstrate that this approach is especially facile and effective when MAA is used to form backbone radicals.…”