Azo-Containing Polymers with Degradation On-Demand Feature

Abstract

ABSTRACT. Molecules comprising aliphatic azo moieties are widely used as radical polymerization initiators, but only few studies have explored their usefulness as stimuliresponsive motifs in macromolecular constructs. The controlled degradation of azo-containing polymers has indeed remained largely unexplored. Here we present the syntheses of linear azocontaining polyamides and polyurethanes and report on their thermally and optically induced responses in solution and the solid state. We show that the stimuli-induced degradation behavior depends strongly on the nature of the polymer backbone, the state of matter, and in solution, on the nature of the solvent. The stimuli-responsive solid-state properties of the azo-containing materials may be particularly useful. In the case of the polyurethanes studied here, temperatureor light-induced cleavage of the azo motifs led to a controllable decrease of the molecular weight, which in turn caused a reduction of the elongation at break, modulus and strength. The controlled degradation of the polymer in well-defined areas can be readily achieved via photopatterning, and this approach was shown to be useful to produce solid structures with graded mechanical properties.2

Azobenzene‐Containing Block Copolymers as Light‐Induced Reworkable Adhesives: Effects of Molecular Weight, Composition, and Block Copolymer Architectures on the Adhesive Properties

“…From an environmental viewpoint, adhesives that can be dismantled and reworked have recently attracted much attention, because they allow the bonded materials to be separated and recycled after use or defective components to be exchanged during manufacturing processes to improve the production efficiency . Various types of these adhesives have been investigated based on changes in their physical and chemical properties such as heat‐expandable microcapsules, thermal and electrical degradation of polymers, reversible crosslinking reactions, shape memory polymers, and liquid crystalline–isotropic phase transitions . Although most of the reported mechanisms are based on thermal activation, light‐induced systems have the potential to offer distinct characteristics such as activation in an athermal process that focuses on a local adhesion area.…”

Triggered Metal Ion Release and Oxidation: Ferrocene as a Mechanophore in Polymers

“…[36] Relying on previous strategies for the design of mechanically responsive polymers,weused single-electron living radical polymerizations (SET-LRP) [8,37] to prepare poly(methyl acrylate)s having one chain-centered ferrocene motif (Fc-PMA). We further exploited ap olycondensation reaction to synthesize polyurethanes [38] with multiple,s tatistically distributed ferrocene moieties along the backbone (Fc-PU). [39] Them echanoresponse of these materials was studied by monitoring the decrease of the molecular weight of these polymers,i nduced by ultrasonication of dilute solutions.…”

“…In order to increase the number of metal-ion-release events per polymer chain, we also investigated polyurethanes, obtained by ap olycondensation reaction (Scheme 2), with several ferrocene moieties randomly distributed in the polymer backbone. [38,39] Thus, Fc-PU (M n = 100 kDa, = 2.03) with an average ferrocene content of 6F cu nits per chain (3 mol %F c), was synthesized and subjected to an ultrasonication experiment. Ther esults were compared with those obtained for af errocene-free ref-PU of similar molecular weight and dispersity (see SI, Figure S21).…”

(De)bonding on Demand with Optically Switchable Adhesives

“…Ayer et al prepared light‐responsive DMSO‐based organogels by cross‐linking poly(vinyl alcohol) with an aliphatic azo moiety derived from 2,2′‐azobis[2‐methyl‐ N (2‐hydroxyethyl)propionamide] . For optimized compositions (molecular weight of the polymer and cross‐linking degree) of the organogel, a solid‐to‐liquid phase transition could be induced upon exposure to UV or visible light as a consequence of the irreversible decomposition of the azo moieties . A shear strength of 26 kPa was measured for glass lap joints and UV irradiation (λ = 390−500 nm, 600 mW cm −2 ) induced on‐demand debonding within seconds.…”