Linear, Y- and Ψ-shaped poly(2-(dimethylamino)ethyl methacrylate) and poly(methyl methacrylate) brushes prepared by surface-initiated polymerization from a homologous series of ATRP initiators

A series of 3 homologous surface-anchored initiators for atom transfer radical polymerization has been used to graft linear, Y- and Ψ-shaped poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(methyl methacrylate) (PMMA) brushes from silicon surfaces. The film thicknesses of these architecturally different polymer brushes could be tuned both by controlling the polymerization time, as well as (as was shown for the polymerization of 2-(dimethylamino)ethyl methacrylate) by changing the monomer concentration. The library of linear, Y- and Ψ-shaped PDMAEMA and PMMA brushes was used to investigate the possible impact of polymer architecture on the swelling properties as well as the degrafting behavior of these surface-grown polymer films. The swelling of the PDMAEMA and PMMA brushes in PBS, respectively, acetone as a solvent was studied by ellipsometry. These experiments revealed a smaller swelling ratio for Y-shaped polymer brushes, as compared to linear analogues of comparable dry film thickness. Degrafting experiments were conducted with linear, Y- and Ψ-shaped PDMAEMA brushes in PBS. These experiments revealed a 2-fold, respectively, 3-fold increase in the initial rate constant of degrafting for the Y- and Ψ-shaped PDMAEMA brushes as compared to the linear analogues.

本研究采用一系列共3种同源的、用于原子转移自由基聚合（atom transfer radical polymerization）的表面锚定引发剂，从硅表面接枝得到线性、Y形及Ψ形聚(2-(二甲氨基)乙基丙烯酸甲酯)（poly(2-(dimethylamino)ethyl methacrylate, PDMAEMA）与聚甲基丙烯酸甲酯（poly(methyl methacrylate), PMMA）聚合物刷。上述具有不同拓扑结构的聚合物刷膜厚，既可通过调控聚合时间进行调节，也可（如在聚(2-(二甲氨基)乙基丙烯酸甲酯)聚合实验中所证实的那样）通过改变单体浓度实现精准调控。本研究利用该线性、Y形及Ψ形PDMAEMA与PMMA聚合物刷文库，探究了聚合物拓扑结构对这类表面生长聚合物膜的溶胀性能以及脱接枝行为的潜在影响。采用椭偏仪（ellipsometry），本研究分别探究了PDMAEMA聚合物刷在磷酸盐缓冲液（phosphate buffered saline, PBS）以及PMMA聚合物刷在丙酮溶剂中的溶胀行为。实验结果表明，与干膜厚度相当的线性聚合物刷类似物相比，Y形聚合物刷的溶胀比更低。针对线性、Y形及Ψ形PDMAEMA聚合物刷，我们在PBS体系中开展了脱接枝实验。实验结果显示，与线性类似物相比，Y形和Ψ形PDMAEMA聚合物刷的脱接枝初始速率常数分别提升了2倍与3倍。