We describe the 3-iodopropyl acetal
moiety as a simple cleavable
unit that undergoes acid catalyzed hydrolysis to liberate HI (pK
a ∼ −10) and acrolein stoichiometrically.
Integrating this unit into linear and network polymers gives a class
of macromolecules that undergo a new mechanism of degradation with
an acid amplified, sigmoidal rate. This trigger-responsive self-amplified
degradable polymer undergoes accelerated rate of degradation and agent
release.
We report a photo-triggered, base generating, base propagating degradable polyurethane that is triggered by 365 nm UV light irradiation. A small area of this polyurethane material can be exposed to...
Encapsulated anticorrosion agents provide a suitable alternative to dispersion of metal-based compounds in protective polymericcoatings on metal substrates. Stimuli-responsive microcapsules enhance protection abilities by autonomously responding to corrosion-induced environmental changes, rather than relying on damage-induced mechanical stimuli. This work reports pH-responsive microcapsules with triggered release over a wide range of acidic pH values (pH < 6) and robust enough to be incorporated in commercial solvent-based epoxy coatings. The pH responsiveness is achieved by integrating acid labile ketals that undergo rapid hydrolysis within the cross-linked polyamide shell and readily release acetylenic diol or jojoba oil as the anticorrosive agent. The microcapsules are stable up to a temperature of 150 °C and provide long-term room temperature stability up to 3 months. Degradation and release kinetics of the microcapsules are quantified at various pH levels (1 ≤ pH ≤ 9) using 1 H NMR and gas chromatography, respectively. Microcapsules exhibit complete release in under 5 min at pH 1 and ≈2 hours at pH 5, respectively. Coating performance is evaluated by electrochemical corrosion tests conducted in 5 wt% salt solutions with varying pH and concentration of the microcapsules in the coating. Inhibition efficiencies up to 70% are achieved in acidic saltwater solutions.
A major challenge in developing recyclable polymeric materials is the inherent conflict between the properties required during and after its life span. In particular, materials must be strong and durable when in use, but undergo complete and rapid degradation upon end-of-life. We report a new mechanism for degrading polyurethanes called CyclizAtion-Triggered CHain (CATCH) cleavage that achieves this duality. CATCH cleavage features a simple glycerol-based acyclic acetal unit as a kinetic and thermodynamic trap for gated chain-shattering. Thus, an organic acid induces transient chain breaks with oxocarbenium ion formation and subsequent intramolecular cyclization to depolymerize fully the polyurethane backbone at room temperature. With minimal chemical modification, the resulting degradation products can be repurposed into strong adhesives and photochromic coatings demonstrating the potential for upcycling. The CATCH cleavage strategy for low-energy input breakdown and subsequent upcycling may be generalizable to a broader range of synthetic polymers and their end-of-life waste streams.
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