Ye Miao, Zhang Dong, Han Lin, Tejada Jonathon, Ortiz Christine
Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
Soft Matter. 2006 Feb 15;2(3):243-256. doi: 10.1039/b510894b.
Here we report the formation of stimulus-responsive chemically end-grafted "brush-brushes" by synthesizing, mono thiol(end)-functionalized poly(methacrylic acid--ethylene glycol) or poly(MAA--EG) comb-type graft copolymers a combination of protecting group chemistry and atom transfer radical polymerization using the initiator 2-(2,4-dinitrophenylthio)ethyl 2-bromo-2-methyl propionate. The polymers were synthesized with three different molecular weights (15 k, 17 k and 27 k), PEG side chain graft densities (EG/MAA mole ratio = 2.2, 0.4 and 1.9, respectively), and a PEG molecular weight = 1100 and then chemically end-grafted to gold substrates chemisorption, resulting in molecular separation distances of ∼3-4 nm. pH-Dependent swelling was confirmed to take place gradually above pH 4-5 and quantified by heights measured by contact mode AFM imaging of microcontact printed (µCP) samples. Swelling factors (maximum height/minimum height) were fairly large (3.6-7.3) and a decrease in molecular weight by ∼2× and side chain graft density by ∼4× resulted in a decrease in swelling factor by ∼2×. Layer height normal force for all three polymers measured by contact mode atomic force microscope imaging on µCP samples at pH 9 showed a nonlinearly decreasing relationship and complete compression ∼<2 nm for forces >10 nN. At pH 4, all polymer layers were largely collapsed (heights ∼<4 nm) and incompressible (, heights were independent of normal force).
在此，我们报告通过合成单硫醇（末端）官能化的聚（甲基丙烯酸 - 乙二醇）或聚（MAA - EG）梳型接枝共聚物，利用2 - （2,4 - 二硝基苯硫基）乙基2 - 溴 - 2 - 甲基丙酸酯引发剂，结合保护基团化学和原子转移自由基聚合，形成刺激响应性化学端接枝的“刷 - 刷”结构。合成的聚合物具有三种不同的分子量（15k、17k和27k）、聚乙二醇侧链接枝密度（EG/MAA摩尔比分别为2.2、0.4和1.9）以及聚乙二醇分子量 = 1100，然后通过化学吸附端接枝到金基底上，分子分离距离约为3 - 4nm。证实pH依赖性溶胀在pH 4 - 5以上逐渐发生，并通过微接触印刷（µCP）样品的接触模式原子力显微镜成像测量的高度进行量化。溶胀因子（最大高度/最小高度）相当大（3.6 - 7.3），分子量降低约2倍和侧链接枝密度降低约4倍导致溶胀因子降低约2倍。通过接触模式原子力显微镜对pH 9的µCP样品成像测量的所有三种聚合物的层高度法向力显示出非线性下降关系，对于大于10 nN的力，完全压缩至约<2 nm。在pH 4时，所有聚合物层基本塌陷（高度约<4 nm）且不可压缩（高度与法向力无关）。
