Nondestructive Photo-Cross-Linking of Microphase-Separated Diblock Polymers through Coumarin Dimerization

Abstract

The effect of long-wavelength ultraviolet photo-cross-linking on microphase-separated coumarin-containing block polymers was studied by photorheometry and small-angle X-ray scattering. This model system consisted of three photo-cross-linkable diblock polymers of poly­(methoxyethyl acrylate)-b-poly­(hexyl methacrylate-co-coumarin methacrylate) with different volume fractions of the cross-linkable coumarin-containing block, which microphase separated into lamellar and cylindrical morphologies. All polymers stiffened upon exposure to 365 nm light, with much greater relative increases in moduli recorded for lamellae-forming polymers (ca. 3200% increase) compared to the cylinder-forming polymer (ca. 550% increase). Disordering transitions that were evident in un-cross-linked samples were no longer observed after cross-linking in the ordered state, and domain sizes were found to remain stable to heating. The photo-cross-linking reaction only proceeded under active irradiation (i.e., cross-linking does not persist when the UV radiation is turned off), indicating a high degree of spatiotemporal control over curing in this system. Finally, at constant concentration of couamarin within the cross-linkable block, the cure rate was largely independent of polymer composition, suggesting a constant local concentration of coumarin moieties within the segregated cross-linkable domains. These findings establish a set of specific structure–property relationships governing the phase-selective photo-cross-linking of diblock polymers that can guide the design of robust nanostructured materials.

Preparation of coumarin polymer grafted nanocellulose films to form high performance, photoresponsive barrier layers

“…ATRP polymerization is highly thought of in this research to obtain uniform polymer chain length on cellulose surfaces. The uniform chain length of the polymer containing the coumarin pendent group will be highly susceptible to crosslinking with adjacent (intermolecular) coumarin molecules when they are subjected to UV crosslinking, similar to what was explained in literature 25–27 …”

“…The uniform chain length of the polymer containing the coumarin pendent group will be highly susceptible to crosslinking with adjacent (intermolecular) coumarin molecules when they are subjected to UV crosslinking, similar to what was explained in literature. [25][26][27] 2.2.4 | Quantification of Br group in macroinitiator and cu in NC-polymer ICP-MS analysis of macroinitiators (A), (B) and (C) show 1.4 ± 0.1, 4 ± 0.2, and 7.7 ± 0.1 wt.% of Br group in macroinitiators (Standard calibration curve is shown in Figure S4).…”

“…Some of the studies have adapted controlled living radical polymerization, especially ATRP, for preparing a well-defined polymeric structure with coumarin, such as coumarin functionalized dendritic-star polymers. 25,26 In those papers, they stated the ATRP gave a well-defined structure (with controllable chain length) therefore coumarin-coumarin crosslinking was possible between adjacent arms of the dendrimer-star copolymers. 27 In this research, ATRP is used to control length of the polymer in similar way to enhance the cross-linking between coumarin molecules from adjacent chains.…”

“…ATRP polymerization promoted the uniform molecular weight distribution of the polymer chains (as per the GPC results). The uniform distribution of coumarin groups on the uniformed polymer chains tends to crosslink to a greater extent (as described in the introduction with examples [25][26][27] ), resulting in a continuous network, which prevents water vapor from passing through the sheet, thereby decreasing the WVTR of the sheets (as per the data in Section 2.4). Improving WVTR using photocrosslinking of coumarin polymer grafted on NC is a new concept proved in this research.…”

Photocrosslinkable Polymeric Bicontinuous Microemulsions

“…In this work, we develop a new approach to crosslink polymeric BμEs using coumarin [2 + 2] photodimerization. This reaction is mediated by long-wavelength UV light and has been utilized in solution-based polymeric systems, − polymer melts, − and microphase-separated diblock polymers. , Importantly, the ability to perform coumarin-based photocrosslinking without exogenous reagents or thermal treatment ensures that the microstructure will be minimally perturbed during curing. In the ternary blends studied herein, we find that coumarin photodimerization can crosslink and covalently stabilize emergent morphologies, including the BμE, with minimal disruption to the microscopic structure.…”