Rapid and Selective Photo‐degradation of Polymers: Design of an Alternating Copolymer with an o‐Nitrobenzyl Ether Pendant

Abstract

The development of polymers with on-demand degradability is required to alleviate the current global issues on polymer-waste pollution. Therefore, we designed a vinyl ether monomer with an o-nitrobenzyl (oNBn) group as a photo-deprotectable pendant (oNBnVE) and synthesized an alternating copolymer with an oNBn-capped acetal backbone via cationic copolymerization with p-tolualdehyde (pMeBzA). The resultant alternating copolymer could be rapidly degraded into lower-molecular-weight compounds upon simple exposure to UV irradiation without any reactants or catalysts, while it was sufficiently stable toward heat and ambient light. This degradation proceeds via cleavage of the hemiacetal structure generated upon photo-deprotection of the oNBn pendant. The oNBnpeculiar degradability allowed the exclusive photodegradation of the oNBnVE/pMeBzA segments in a diblock copolymer composed of oNBnVE/pMeBzA and benzyl vinyl ether (BnVE)/pMeBzA segments.

Photolabile SI-PET-RAFT Initiators for Wavelength-Selective Grafting and De-grafting of Polymer Brushes

“…The resulting diradical excited state can undergo photoisomerization to form an aci-nitro intermediate, from which rearrangement yields an o -nitrosobenzaldehyde under release of well-defined chemical groups . The popularity of o -nitrobenzyl photolabile linkers originates, in part, from the ability to modulate photochemical cleaving rates through substitution to the tunability of target photocleaving wavelength. , These properties allow o -nitrobenzyl compounds to impact various fields of research, from solid-phase synthesis to release of chemical payload (e.g., in drug delivery), to decomposition of polymer networks, or degrafting of monolayers of grafted-to polymers …”

“…45 The popularity of onitrobenzyl photolabile linkers originates, in part, from the ability to modulate photochemical cleaving rates through substitution 43 to the tunability of target photocleaving wavelength. 46,47 These properties allow o-nitrobenzyl compounds to impact various fields of research, from solid-phase synthesis 45 to release of chemical payload (e.g., in drug delivery), 48 to decomposition of polymer networks, 49 or degrafting of monolayers of grafted-to polymers. 50 This contribution describes the successful synthesis of a SI-PET-RAFT photolabile initiator (see Figure 2).…”

Umpolung Isomerization in Radical Copolymerization of Benzyl Vinyl Ether with Pentafluorophenylacrylate Leading to Degradable AAB Periodic Copolymers

“…In most cases, the resultant (co)polymers are made of the repetitive carbon–carbon bond, and the robust backbone causes difficulty in the decomposition into low molecular weight compounds, i.e., monomers or other valuable chemicals. Recently, some efforts have been made to introduce the cleavable bond in the repetitive carbon‐carbon bonded backbone [35–58] or the trigger in the pendant [59–66] /terminal [67–72] for the promotion of backbone decomposition. For example, the use of a cyclic ketene acetal as a co‐monomer in radical polymerization of commodity olefin monomer allows the introduction of ester bonds in the backbone, and thus the resultant copolymer becomes degradable under basic conditions (Figure 1B).…”

Hydrogels Containing o-Nitrobenzyl Ester at Cross-Linking Points: Soft Matters for Fabrication of Functionalizable Microwells

“…A commonly used light-sensitive functional group is the o -nitrobenzyl ester (ONB) group due to its high sensitivity and acceptable UV wavelength requirement for biological applications (365 nm). After exposure to UV light, the ONB group decomposes forming a nitroso­benzaldehyde (or a nitrosoketone) and a carboxylic acid (or an alcohol) (see related articles for the mechanism). − Using the ONB group, UV irradiation enables patterning after the synthesis of the gel, even after cell cultivation . The ONB group has been utilized for the preparation of photoresponsive moieties in polymer films, nanoparticles, and patterning of 3D networks by partial de-cross-linking …”