Programming Photodegradability into Vinylic Polymers via Radical Ring‐Opening Polymerization

Abstract

Incorporation of photolabile moieties into the polymer backbone holds promise to remotely-control polymer degradation. However, suitable synthetic avenues are limited, especially for radical polymerizations. Here we report a strategy to program photodegradability into vinylic polymers by exploiting the wavelength selectivity of photocycloadditions for radical ring-opening polymerization (rROP). Irradiation of coumarin terminated allylic sulfides with UVA light initiated intramolecular [2+2] photocycloaddition producing cyclic macromonomers. Subsequent RAFTmediated rROP with methyl acrylate yielded copolymers that inherited the photoreactivity of the cyclic parent monomer. Irradiation with UVB initiated efficient photocycloreversion of the coumarin dimers, causing polymer degradation within minutes under UVB light or days under sunlight exposure. Our synthetic strategy may pave the way to insert photolabile linkages into vinylic polymers, tuning degradation for specific wavelengths.

Main chain selective polymer degradation: controlled by the wavelength and assembly

“…Meanwhile, a new resonance p1 of the resulting vinylarene proton d = 7.70 ppm arises in copolymer P1, conrming the ring-opening polymerization of the cyclic monomer. 18,36 The incorporation ratio of the styrylpyrene monomer and DMA determined from the integral of resonances p 1 and the methyl proton of DMA was 1.8%, slightly lower than the feed ratio. Monitoring the copolymerisation of SC5 and DMA revealed that while the conversion of both monomers increased with polymerisation time, the conversion of SC5 remains slightly below DMA over the entire polymerisation time (Fig.…”

“…As SC5 is the only monomer within P3 that absorbs light at l = 360 nm (as shown in Fig. 1B), 36,52 the SEC-UV trace of P3 at l = 360 nm was used to investigate the origin of the shoulder of P3. The SEC-UV trace of P3 thus only represents the chain-extension product, i.e.…”

“…35 To exploit the spatiotemporal control of light gated reactions to steer polymer main chain transformations, we have recently designed an allylic sulde containing coumarin photocycloadduct, which provided access to photodegradable vinyl polymers. 36 In addition to spatiotemporal reaction control of photoreactions, different molecules can absorb light of different wavelengths, offering additional energetic control over reactions: specic photon energies can initiate selective reactions. [37][38][39][40] Here we report the main chain selective degradation of vinylic block-copolymers, where specic blocks are ondemand degraded into oligomers in response to different wavelengths of light (Scheme 1).…”

Photochemical Action Plots Reveal the Fundamental Mismatch Between Absorptivity and Photochemical Reactivity

“…To this end, Do et al demonstrated a polymer ligation system where UVA light was used to polymerise a multicomponent polymer and shorter wavelength UVB light was later applied for degradation. [25] Action plots are perhaps even more critical where two colors of light are required to facilitate a photochemical reaction, such as in emerging 3D printing technologies. Here, they are essential to determine the specific wavelengths where individual chromophores, or synthetic steps, can be addressed individually for synergistic, orthogonal, antagonistic or sequential purposes.…”

“…To this end, Do et al demonstrated a polymer ligation system where UVA light was used to polymerise a multicomponent polymer and shorter wavelength UVB light was later applied for degradation. [ 25 ]…”