Azomethine‐Containing Pyrrolo[3,2‐b]pyrrole Copolymers for Simple and Degradable Conjugated Polymers

Abstract

Conjugated polymers have received significant attention as potentially lightweight and highly tailorable alternatives to inorganic semiconductors, but their synthesis is often complex, produces toxic byproducts, and they are not typically designed to be degradable or recyclable. These drawbacks necessitate dedicated efforts to discover materials with design motifs that enable targeted and efficient degradation of conjugated polymers. In this vein, the synthetic simplicity of 1,4‐dihydropyrrolo[3,2‐b]pyrroles (DHPPs) is exploited to access azomethine‐containing copolymers via a benign acid‐catalyzed polycondensation protocol. Polymerizations involve reacting a dialdehyde‐functionalized dihydropyrrolopyrrole with p‐phenylenediamine as the comonomer using p‐toluenesulfonic acid as a catalyst. The inherent dynamic equilibrium of the azomethine bonds subsequently enabled the degradation of the polymers in solution in the presence of acid. Degradation of the polymers is monitored via NMR, UV‐vis absorbance, and fluorescence spectroscopies, and the polymers are shown to be fully degradable. Notably, while absorbance measurements reveal a continued shift to higher energies with extended exposure to acid, fluorescence measurements show a substantial increase in the fluorescence response upon degradation. Results from this study encourage the continued development of environmentally‐conscious polymerizations to attain polymeric materials with useful properties while simultaneously creating polymers with structural handles for end‐of‐life management or/and recyclability.

Direct Arylation Polymerization of Degradable Imine-Based Conjugated Polymers

“…30 Collier and co-workers leveraged the diverse properties and synthetic versatility of the dihydropyrrolo [3,2b]pyrrole monomeric scaffold to synthesize a new degradable polymer furnished with imine bonds. 23 Work from our group demonstrated that biobased monomers from carotenoids can give rise to imine-based, carotenoid-phenylenediamine polymers, which resemble the structure of polyacetylene. 31 The emergence of new polymers relies on robust and efficient polymerization methods to afford well-defined polymers.…”

“…17 In some instances, degradation can also lead to the recovery of the starting monomers, establishing a circular closed-end loop through recyclability. 22,23 Although these linkages have been investigated, they often compromise electrical performance. Recent work has demonstrated that conjugated polymers containing imine bonds can be readily degraded via acid hydrolysis while maintaining electronic performance comparable to their nondegradable vinyl counterpart.…”

“…Since then, Bao and co-workers have explored the tunability of the degradation lifetimes of TIT-based conjugated polymers . Collier and co-workers leveraged the diverse properties and synthetic versatility of the dihydropyrrolo­[3,2- b ]­pyrrole monomeric scaffold to synthesize a new degradable polymer furnished with imine bonds . Work from our group demonstrated that biobased monomers from carotenoids can give rise to imine-based, carotenoid-phenylenediamine polymers, which resemble the structure of polyacetylene .…”

“…The reversibility between doped and undoped of imine-based conjugated polymers with acid and base treatment, respectively, has been well-documented in the literature. 23,60 Due to the limitations of our experimental setup, where we can only study the doping of p(IDT−TIT) with saturated TFA vapors in a cuvette, we hypothesize that p(IDT−TIT) is undoped due to atmospheric conditions entering the cuvette as the TFA vapor evaporates. The pronounced spectroscopic and color changes in thin films and in solution as a result of protonic acid-doping suggest that p(IDT−TIT) displays sensor-like properties and is consistent with previous studies.…”

“…Through judicious monomer and polymer designs, degradation can occur from an external stimulus, such as a specific change in physiological conditions, allowing for fine-tuning of degradation lifetimes . In some instances, degradation can also lead to the recovery of the starting monomers, establishing a circular closed-end loop through recyclability. , Although these linkages have been investigated, they often compromise electrical performance. Recent work has demonstrated that conjugated polymers containing imine bonds can be readily degraded via acid hydrolysis while maintaining electronic performance comparable to their nondegradable vinyl counterpart. , Moreover, the tunable optoelectronic properties of imine-based conjugated polymers have also been extensively investigated by Skene and co-workers. − The scope of imine-based conjugated polymers established by these earlier reports has since motivated new monomer and polymer designs.…”