Multifunctional Photodegradable Polymers for Reactive Micropatterns

We report the first example of realizing the multifunctionalization of photodegradable polymers for the preparation of reactive micropatterns. Three o-nitrobenzaldehyde monomers (M1, M2, and M3) with allyl, propargyl, and epoxy groups were synthesized in high yields by the simple reactions of 5-hydroxy-2-nitrobenzaldehyde with allyl bromide, propargyl bromide, and epichlorohydrin, respectively. Passerini multicomponent polymerization (Passerini MCP) of M1, M2, or M3 with 1,6-hexanedioic acid and 1,6-diisocyanohexane generated three poly­(ester–amide)­s (P1, P2, and P3), the ester linkages of which were o-nitrobenzyl derivatives with functional groups from the corresponding monomers. Therefore, these polymers are photodegradable and can also be further modified by efficient click reactions like thiol–ene, copper catalyzed azide–alkyne cycloaddition (CuAAC), and epoxy–amine reaction. Furthermore, Passerini MCP of M1, M2, and M3 with 1,6-hexanedioic acid and 1,6-diisocyanohexane could yield a photodegradable triply functional polymer (P4) containing all the three functional side groups which can be further modified by sequential click reactions. All the polymers were thoroughly characterized by ¹H NMR and GPC. Degradation of the polymers in solution under UV irradiation was investigated by UV–vis and GPC, and they can all be photocleaved into oligomers and small molecules in 30 min. These functional polymers are extremely useful as positive photoresists to create reactive micropatterns. As an example, the triply functional polymer film was fabricated and cross-linked by epoxy–amine reaction. After photoirradiation under a mask, reactive patterns with allyl and propargyl groups were obtained. Sequential modification of the reactive sites by CuAAC and thiol–ene reactions afforded multifunctional patterned surfaces with tunable properties as confirmed by scanning electron micrograph (SEM) and confocal fluorescence microscopy.