Spatial control over cross-linking dictates the pH-responsive behavior of poly(2-(tert-butylamino)ethyl methacrylate) brushes.
Spatial control over cross-linking dictates the pH-responsive behavior of poly(2-(tert-butylamino)ethyl methacrylate) brushes.
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DOI：
10.1021/la403666y
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发表时间：
2014-02-11
期刊：
影响因子：
--
通讯作者：
Armes SP
中科院分区：
文献类型：
--
作者：
Alswieleh AM;Cheng N;Leggett GJ;Armes SP
表面引发原子转移自由基聚合(ATRP)制备的甲基丙烯酸叔丁氨基乙酯(TBAEMA)具有pH响应性的仲胺功能化聚合物刷，用椭偏仪测定，其干厚度在4~28 nm之间。在低pH下，线性PTBAEMA刷子质子化并高度膨胀；当溶液pH增加到约7.7时，由于去质子化，刷子坍塌。随后用甲苯-2，4-二异氰酸酯封端的聚丙二醇酯(PPG-TGI)在四氢呋喃(PTBAEMA的良好溶剂)或正己烷(劣质溶剂)中对PTBAEMA刷子进行了交联。与PPG-TDI反应后，C1S X射线光电子能谱中的C-C-O组分(286.5 eV)的强度增加，表明两种溶剂都成功地进行了交联。椭偏仪研究表明，这些交联剂的pH响应行为是由PPG-TDI交联剂的空间位置决定的。因此，与用正己烷制备的表面交联型刷子相比，在四氢呋喃中制备的均匀交联型刷子在给定的(低)pH值下变得略微不那么膨胀。通过紫外光照射和干涉光刻分别制备了微米和纳米PTBAEMA电刷，并用原子力显微镜对其进行了表征。刷子高度的变化被确定为pH的函数，这些AFM观察结果与椭圆偏振研究密切相关。
Surface-initiated atom transfer radical polymerization (ATRP) of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) produced pH-responsive secondary amine-functionalized polymer brushes with dry thicknesses ranging from 4 to 28 nm, as determined by ellipsometry. At low pH, linear PTBAEMA brushes became protonated and highly swollen; brush collapse occurred when the solution pH was increased to ca. 7.7 due to deprotonation. PTBAEMA brushes were subsequently cross-linked using tolylene-2,4-diisocyanate-terminated poly(propylene glycol) (PPG-TGI) in either THF (a good solvent for PTBAEMA) or n-hexane (a poor solvent). The intensity of the C–C–O component (286.5 eV) in the C1s X-ray photoelectron spectrum increased after reaction with PPG-TDI, suggesting that cross-linking was successful in both solvents. Ellipsometry studies indicated that the pH-responsive behavior of these cross-linked brushes is dictated by the spatial location of the PPG-TDI cross-linker. Thus, uniformly cross-linked brushes prepared in THF became appreciably less swollen at a given (low) pH than surface-cross-linked brushes prepared in n-hexane. Micro- and nanopatterned PTBAEMA brushes were prepared via UV irradiation and interference lithography, respectively, and characterized by atomic force microscopy. The change in brush height was determined as a function of pH, and these AFM observations correlated closely with the ellipsometric studies.
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