Effect of Overall Grafting Density on Microphase Separation of Mixed Homopolymer Brushes Synthesized from Y-Initiator-Functionalized Silica Particles

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• 作者：Chunhui Bao ; Saide Tang ; Jonathan M. Horton ; Xiaoming Jiang ; Ping Tang ; Feng Qiu ; Lei Zhu ; Bin Zhao
• 刊名：Macromolecules
• 出版年：2012
• 出版时间：October 9, 2012
• 年：2012
• 卷：45
• 期：19
• 页码：8027-8036
• 全文大小：739K
• 年卷期：v.45,no.19(October 9, 2012)
• ISSN：1520-5835

文摘

We report in this article a systematic study on the effect of overall grafting density (蟽_overall) on microphase separation of mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brushes synthesized from asymmetric difunctional initiator (Y-initiator)-functionalized silica particles. The initiator particles were made by the immobilization of a triethoxysilane-terminated Y-initiator on the surface of 173 nm silica particles via an ammonia-catalyzed hydrolysis/condensation process in ethanol. Mixed PtBA/PS brushes were then grown from initiator particles by surface-initiated atom transfer radical polymerization of tBA at 75 掳C and nitroxide-mediated radical polymerization of styrene at 120 掳C. By changing the mass ratio of Y-initiator to silica particles in the initiator immobilization step, we found that the overall grafting density of mixed brushes can be systematically tuned while the individual grafting densities of two polymers remained comparable. A series of mixed PtBA/PS brushes with molecular weights of 23 kDa for both PtBA and PS and 蟽_overall from 1.06 to 0.122 chains/nm² were prepared. Their microphase separation behavior was studied by transmission electron microscopy after the samples were drop-cast from chloroform onto carbon-coated TEM grids, annealed with CHCl₃ vapor, and stained with RuO₄. CHCl₃ is a good solvent for both grafted polymers. When the 蟽_overall was 0.34 chains/nm² and above, the mixed PtBA/PS brushes underwent lateral microphase separation, forming 鈥渞ippled鈥?nanostructures. The ripple wavelength (D) increased with decreasing 蟽_overall; the normalized D scaled with 蟽_overall^鈥?.47 in the 蟽_overall range of 1.06鈥?.54 chains/nm². With further decreasing the grafting density, the phase separation became weaker, and no microphase separation was observed in the sample with 蟽_overall of 0.122 chain/nm².