Thickness-dependent properties of polyzwitterionic brushes
Thickness-dependent properties of polyzwitterionic brushes
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DOI：
10.1021/ma800625y
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发表时间：
2008-09-09
期刊：
影响因子：
5.5
通讯作者：
Huck, Wilhelm T. S.
中科院分区：
文献类型：
--
作者：
Cheng, Nan;Brown, Andrew A.;Huck, Wilhelm T. S.
本文描述了从引发剂改性金表面可控合成聚[2-(甲基丙烯酰氧基)乙基]二甲基(3-磺丙基)氢氧化铵(polyMEDSAH)的详细研究，以及这些刷的性能随接枝密度和厚度的变化。通过预形成催化活性络合物以确保单体不与催化剂配位，实现了对聚合的改进控制。我们观察到一个有趣的转变厚度（h（crit）），其中由于强的链间和链内缔合，聚MEDSAH刷从亲水性转变为疏水性。我们研究了这种转变作为聚合速率和接枝密度的函数，发现这两个因素都强烈影响 h(crit) 的值。生长较快的 PolyMEDSAH 刷子具有较高的 h(crit) 值，而由较高的接枝密度生长的刷子具有较高的 h(crit) 值。这些观察结果表明，h(crit) 受刷子密度、聚合物链长度和排列程度的控制。此外，链间或链内缔合可以通过升高温度来逆转，导致疏水性到亲水性的转换，其中转换的幅度由接枝密度决定。
This paper describes detailed studies on the controlled synthesis of poly [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide (polyMEDSAH) from initiator-modified gold surfaces and the properties of these brushes as a function of grafting density and thickness. Improved control over polymerization was achieved by preforming the catalytically active complex to ensure that the monomers did not coordinate to the catalyst. We observed an intriguing transition thickness (h(crit)) in which the polyMEDSAH brushes switched from hydrophilic to hydrophobic due to the strong inter- and intrachain associations. We studied this transition as a function of the rate of polymerization and grafting density and found that both factors strongly influence the value of h(crit). Faster grown polyMEDSAH brushes have higher h(crit) values, and brushes grown from higher graffing density have higher h(crit) value. These observations suggest that the h(crit) is governed by the density of the brushes, the polymer chain length, and the degree of alignment. Furthermore, the inter- or intrachain associations can be reversed by increasing the temperature, leading to a hydrophobic to hydrophilic switch, where the magnitude of the switching is governed by the grafting density.