Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire S3 7HF, United Kingdom.
Langmuir. 2010 May 18;26(10):7216-26. doi: 10.1021/la904346j.
Surface-initiated atom transfer radical polymerization (SI-ATRP) has been used to grow brushes of poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) from silicon wafers using a polyelectrolytic macroinitiator on planar silicon wafers. Film thicknesses of up to 450 nm were possible within 21 h, and the effect of adding activator and deactivator species on the brush growth rate was studied. The solvation of PMPC brushes in mixed alcohol/water solvents was investigated using in situ ellipsometry. Co-nonsolvency (a re-entrant swelling transition) behavior was observed in water/ethanol binary mixtures; that is, the PMPC brushes were highly swollen in either pure ethanol or water but became deswollen at specific ethanol-rich solvent compositions. A similar effect was obtained with water/2-propanol mixtures, except that in this case pure 2-propanol was not a particularly good solvent for the PMPC chains. However, co-nonsolvency was not observed for water/methanol binary mixtures, since the brushes remained well swollen at all solvent compositions. This is consistent with prior reports of co-nonsolvency effects in both PMPC gels and linear PMPC chains. However, this is the first report of this phenomenon for PMPC brushes and one of the first examples of co-nonsolvency observed for any polymer brush system. A direct comparison of brush and gel swelling reveals an approximate power-law relationship between the equilibrium volumes of these two systems at various solvent compositions, which is interpreted by treating the brush layer as a surface-attached gel. We believe this to be the first quantitative comparison of brush and gel swelling using the same polymer under the same conditions. The kinetics of the PMPC brush response to adjustment of the alcohol/water composition is relatively fast, with the brush volume change occurring on time scales of less than 1 min as judged by in situ ellipsometry.
表面引发原子转移自由基聚合（SI-ATRP）已被用于从硅片上生长聚（2-（甲基丙烯酰氧基）乙基磷酸胆碱）（PMPC）刷，使用平面硅片上的聚电解质大分子引发剂。在 21 小时内可以达到高达 450nm 的膜厚，并研究了添加活化剂和失活剂对刷增长速率的影响。使用原位椭圆光度法研究了 PMPC 刷在混合醇/水溶剂中的溶剂化作用。在水/乙醇二元混合物中观察到共非溶剂（再进入溶胀转变）行为；也就是说，PMPC 刷在纯乙醇或水中高度溶胀，但在特定富乙醇溶剂组成下变得溶胀。在水/2-丙醇混合物中也获得了类似的效果，只是在这种情况下，纯 2-丙醇不是 PMPC 链的特别好的溶剂。然而，在水/甲醇二元混合物中没有观察到共非溶剂效应，因为在所有溶剂组成下，刷仍然高度溶胀。这与 PMPC 凝胶和线性 PMPC 链中均观察到共非溶剂效应的先前报道一致。然而，这是首次报道 PMPC 刷中出现这种现象，也是首次观察到任何聚合物刷系统中的共非溶剂现象之一。刷和凝胶溶胀的直接比较揭示了这两个系统在各种溶剂组成下的平衡体积之间的近似幂律关系，通过将刷层视为表面附着的凝胶来解释。我们相信这是首次使用相同聚合物在相同条件下对刷和凝胶溶胀进行定量比较。根据原位椭圆光度法判断，PMPC 刷对调整醇/水组成的响应动力学相对较快，刷体积变化发生在不到 1 分钟的时间尺度内。
