Unexpected Folding of Bottlebrush Polymers in Melts
Unexpected Folding of Bottlebrush Polymers in Melts
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DOI：
10.1021/acs.macromol.2c02053
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发表时间：
2023-01-27
期刊：
影响因子：
5.5
通讯作者：
Cai, Li-Heng
中科院分区：
文献类型：
--
作者：
Nian, Shifeng;Huang, Baiqiang;Cai, Li-Heng
瓶刷分子是具有长线性主链的支化聚合物，其被许多相对短的线性侧链密集接枝。这种独特的分子结构使瓶刷聚合物具有线性对应物无法达到的性质和功能。现有的理解是，在瓶刷聚合物的熔体中，主链间距离随着侧链的接枝密度变小而减小。在这里，我们实验发现的行为相反，所有现有的工作：主链间的距离单调增加的接枝密度降低。为了解释这些显着的实验结果，我们开发了一个理论，占的主链和侧链之间的不相容性内瓶刷分子。主链聚合物折叠成圆柱形核，所有接枝位点在其表面上以降低界面自由能。随着接枝密度的降低，主链塌陷;该过程不仅增加了圆柱形核的直径，而且还减小了空间中接枝位点之间的距离，使得侧链的延伸没有减轻。我们的发现提出了一个范式转变的了解瓶刷聚合物的分子结构。
Bottlebrush molecules are branched polymers with a long linear backbone densely grafted by many relatively short linear side chains. Such a unique molecular architecture enables bottlebrush polymers with properties and functions inaccessible by their linear counterparts. The existing understanding is that, in melts of bottlebrush polymers, the interbackbone distance decreases as the grafting density of side chains becomes smaller. Here, we experimentally discover a behavior opposite to all existing works: the interbackbone distance increases monotonically as the grafting density decreases. To explain these remarkable experimental findings, we develop a theory by accounting for the incompatibility between the backbone and side chains within a bottlebrush molecule. The backbone polymer folds into a cylindrical core with all grafting sites on its surface to reduce interfacial free energy. As the grafting density decreases, the backbone collapses; this process not only increases the diameter of the cylindrical core but also reduces the distance between grafting sites in space, such that the extension of side chains is not alleviated. Our discovery presents a paradigm-shifting understanding of the molecular structure of bottlebrush polymers.