Radical ring-opening polymerisation (RROP) of cyclic ketene acetals (CKAs) is a powerful avenue for the synthesis of biodegradable polyesters with the potential to replace non-decomposable conventional polymers. The radical polymerisation of CKAs is – surprisingly – accelerated by UV light, yet to-date the cause of the acceleration is unknown. We herein demonstrate how highly wavelength-resolved photochemical action plots of the light-induced RROP of 2-methylene-1,3,6-trioxocane (MTC) provide key information for understanding the light-prompted acceleration. We showcase that two wavelengths, 275 and 350 nm, are critical for the acceleration, with the first one facilitating the ring-opening step of the key CKA-intermediate and the second one promoting free radical initiator decay in a wavelength-orthogonal fashion. In contrast to previous studies, we aimed at unravelling the photochemically-driven monomer conversion by performing RROP at room temperature. Computational studies on the MTC radical formed during RROP indicated the cause of the acceleration: A delocalisation of the radical within the ring, which are calculated to be excited by wavelengths close to those identified experimentally. Thus, remarkably, 275 nm light critically accelerates the rate-determining ring-opening step during RROP, suggesting that photons can be used as a traceless reagent in an unexpected fashion to expedite RROPs.

中文翻译：

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光化学作用图证据 UV 促进环状乙烯酮缩醛的自由基开环聚合


环状乙烯酮缩醛 （CKA） 的自由基开环聚合 （RROP） 是合成可生物降解聚酯的有力途径，有可能取代不可分解的传统聚合物。令人惊讶的是，CKA 的自由基聚合被紫外线加速，但迄今为止加速的原因尚不清楚。我们在此展示了 2-亚甲基-1,3,6-三氧噁烷 （MTC） 光诱导的 RROP 的高度波长分辨光化学作用图如何为理解光提示加速提供关键信息。我们展示了 275 和 350 nm 这两个波长对加速至关重要，第一个波长促进了关键 CKA 中间体的开环步骤，第二个波长以波长正交方式促进自由基引发剂衰变。与以前的研究相比，我们的目标是通过在室温下进行 RROP 来解开光化学驱动的单体转化。对 RROP 期间形成的 MTC 自由基的计算研究表明了加速的原因：自由基在环内的离域，据计算，该自由基被接近实验确定的波长激发。因此，值得注意的是，275 nm 光在 RROP 期间关键地加速了确定速率的开环步骤，这表明光子可以以意想不到的方式用作无痕试剂来加速 RROP。