Microphase-separated polymers hold significant potential for engineering materials with orthogonal properties. However, many applications (e.g., ion conduction, filtration, reprocessable thermosets) require usage in conditions that may disrupt the delicate state of microscopic order. Herein, we describe the usage of coumarin photodimerization to achieve phase-selective photocrosslinking, potentially stabilizing the ordered states against physical, chemical, and thermal disruption. Controlled radical polymerization was used to synthesize coumarin-containing block polymers with varying compositions that microphase separate into defined morphologies, and photo-rheometry enabled real-time monitoring of the photocrosslinking reaction. Little morphological change occurred after crosslinking, indicating that coumarin photodimerization causes minimal perturbation of ordered domains. Disordering transitions that were evident in uncrosslinked samples no longer occurred after crosslinking in the ordered state, and domain sizes remained stable to heating, providing evidence that chain motion and exchange between domains were suppressed. Furthermore, the relative change in modulus after crosslinking strongly depended on the specific state of microstructural order, with lamellar materials exhibiting the strongest modulus increase. These findings establish a set of design rules and structure-property relationships for crosslinked microphase separated polymers that can guide the design of robust nanostructured materials.

Non-destructive photocrosslinking of ordered block polymer materials

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ACS Fall 2022

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