杂化树枝状高分子作为分子对象：熔体中的粘弹性,Macromolecules

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杂化树枝状高分子作为分子对象：熔体中的粘弹性
Macromolecules ( IF 5.1 ) Pub Date : 2019-09-24 , DOI: 10.1021/acs.macromol.9b01412
Salvatore Costanzo _{1,

2,

3} , Leon Scherz ₄ , George Floudas _{5,

6} , Rossana Pasquino ₃ , Martin Kröger ₄ , A. Dieter Schlüter ₄ , Dimitris Vlassopoulos _{1,

2}

Affiliation

结合了两种先前报道的方法，合成了第二代和第三代的两个同源系列的树枝状聚合物（DP），它们具有不同的骨架聚合度。首先，通过相应的甲基丙烯酸酯大分子单体的自由基聚合制备第一代基于甲基丙烯酸酯的DP。由于此类第一代DP的侧支可以形成氢键和π–π堆栈，因此它们被称为“经典”（分子间相互作用）DP。第二，将如此制备的第一代DP接枝有分支的低聚乙二醇基团，以将树突的大小增加到第二代和第三代。由于最外部世代相对于内部最新一代的化学结构不同，这些DP被称为“混合” DP。基于乙二醇的世代不形成分子间的超分子缔合，因此强烈控制相互作用的DP的老化动力学和粘弹性质。因此，一系列的混合DP允许研究由于超分子相互作用和拓扑减少或缺乏协同作用的DP的动力学。乍看之下，我们惊讶地发现，分子间外围相互作用的丧失极大地增加了平衡时间。关于第二代杂种的粘弹性行为，在低频下观察到整体松弛的发生。这与具有相同世代和相同主链聚合度的超分子DP相反，先前已经证明了该超分子DP具有清晰的高原区域。此外，弹性模量的低频平稳区随着骨架聚合度的增加而增加，这表明一种低聚乙烯的生成不足以完全屏蔽分支之间的超分子相互作用。原子模拟也支持这种情况。第三代的混合DP显示了两个不同的储能模量的平稳区域。第一个（频率较高）约为10 第三代的混合DP显示了两个不同的储能模量的平稳区域。第一个（频率较高）约为10 第三代的混合DP显示了两个不同的储能模量的平稳区域。第一个（频率较高）约为10⁶ Pa，并且归因于侧分支的互穿，第二个约为10 ³ Pa。与第二代杂化DP的行为相反，主链的聚合度对低第三代混合DP的频率平稳期。这表明超分子相互作用对弹性平台没有贡献。因此，我们将其归因于整个混合DP的纠缠。所报告的结果汇总在一个表中，该表比较了不同DP的性能，并提供了用于调整此类超支化聚合物流变性的所需成分。

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Hybrid Dendronized Polymers as Molecular Objects: Viscoelastic Properties in the Melt

Two homologous series of dendronized polymers (DPs) of the second and third generations, with different degrees of polymerization of the backbone, were synthesized combining two previously reported approaches. First, methacrylate-based DPs of the first generation were prepared via radical polymerization of the corresponding methacrylate macromonomers. As the side branches of such first-generation DPs can form hydrogen bonds and π–π stacks, they are referred to as “classic” (intermolecularly interacting) DPs. Second, the first-generation DPs so prepared were grafted with branched oligoethylene glycol groups to increase the size of the dendrons up to the second and third generations. Because of the different chemical structures of the outermost generations with respect to the inner one, these DPs are termed “hybrid” DPs. The glycol-based generations do not form intermolecular supramolecular associations, which so strongly control the aging dynamics and viscoelastic properties of the interacting DPs. Therefore, the series of hybrid DPs allow for investigating the dynamics of DPs for which synergistic effects because of supramolecular interactions and topology are reduced or absent. We find, at first glance surprisingly, that the loss of intermolecular peripheral interactions increases the equilibration time dramatically. Concerning the viscoelastic behavior of the hybrids of the second generation, the onset of global relaxation is observed at low frequencies. This is in contrast with supramolecular DPs having the same generation and the same backbone degree of polymerization, for which a clear plateau region was previously demonstrated. In addition, the low-frequency plateau of the elastic modulus increases upon increase of the degree of polymerization of the backbone, suggesting that one oligoethylene generation does not suffice to completely shield supramolecular interactions between the branches. Such a scenario is also supported by atomistic simulations. The hybrid DPs of the third generation display two distinct plateau regions of the storage modulus. The first one (at higher frequencies) is of the order of 10⁶ Pa, and attributed to the interpenetration of the side branches, the second is of the order of 10³ Pa. In contrast with the behavior of second-generation hybrid DPs, the degree of polymerization of the backbone has no effect on the low-frequency plateau of third-generation hybrid DPs. This suggests that supramolecular interactions do not contribute to the elastic plateau. Hence, we ascribe it to the entanglements of the entire hybrid DPs. The reported results are summarized in a table, which compares the properties of different DPs and provides the needed ingredients for tailoring the rheology of such hyperbranched polymers.

更新日期：2019-09-25

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