Dual-Gated Chain Shattering Based on Light Responsive Benzophenones and Thermally Responsive Diels–Alder Linkages

5 years ago

Dual-Gated Chain Shattering Based on Light Responsive Benzophenones and Thermally Responsive Diels–Alder Linkages

Jan Steinkoenig, Hatice Mutlu, Christopher Barner-Kowollik, Markus M. Zieger

We exploit the light-adaptive characteristics of benzophenone (BP) to introduce a chain-shattering degradation mechanism triggered by light (λ_max = 365 nm, 36 W). Incorporated in every repeat unit via a step-growth polymerization of AA- and BB-type difunctional monomers entailing thermally reversible hetero-Diels–Alder (HDA) linkages, the benzophenone functional group enables the disassembly of the on-demand degradable polymers within a few hours to small molecules. Specifically, the benzophenone unit is photoactivated to reversibly generate a biradicaloid triplet state on each monomer moiety, in which the radicals can recombine in an interchain cross-linking reaction or undergo a reduction process, the latter one being key for the disassembly. The newly formed hydroxyl functionality in the ortho-position to the ester bond induces the chain-shattering process via a subsequent lactonization reaction. The polymerization and the light-triggered degradation were assessed in detail by size-exclusion chromatography and—for the first time performed for chain-shattering polymer systems—by high-resolution electrospray ionization mass spectrometry (HR ESI MS). We unambiguously confirm the degradation mechanism by characteristic transformations during the ring-closure reaction forming lactones as stable intermediates in the chain-shattering reaction. Finally, we demonstrate that the system can rapidly undergo gated and orthogonal thermally induced degradation.

Publisher URL: http://dx.doi.org/10.1021/acs.macromol.7b01115

DOI: 10.1021/acs.macromol.7b01115