Photoresponsive Block Copolymer: Synthesis, Characterization, and Surface Activity Control

详细信息    查看全文

• 作者：Saurabh Shrivastava ; Hideki Matsuoka
• 刊名：Langmuir
• 出版年：2014
• 出版时间：April 15, 2014
• 年：2014
• 卷：30
• 期：14
• 页码：3957-3966
• 全文大小：548K
• 年卷期：v.30,no.14(April 15, 2014)
• ISSN：1520-5827

文摘

Amphiphilic block copolymers bearing chromophores are used to achieve photoresponses upon exposure to suitable light, which alter molecular properties, but the photostimulus surface activity control of amphiphilic block copolymers remains to be elucidated. In this work, a series of novel amphiphilic block copolymers consisting of a carboxymethyl betaine monomer (called GLBT) and 4-ethoxy-4鈥?methacrylamide (EMAAB) with different block ratios have been synthesized using a reversible addition鈥揻ragmentation chain-transfer (RAFT) polymerization process. Copolymers were observed to be self-assembled in the aqueous solution above a critical micelle concentration, which was determined by static light scattering measurements and formed vesicles of 120鈥?70 nm in diameter, at different pH values. Copolymers were found to be surface-active at pH 7 but exhibited non-surface activity at acidic and alkaline pH values. After being irradiated with 360 nm UV light, copolymers showed a significant photoresponse both at the surface and in bulk solution as a result of the photoinduced isomerization of azochromophores. The surface property of copolymers was significantly affected by UV irradiation at pH 7, and block copolymers became non-surface-active. The bulk properties changed considerably upon UV exposure where polymer vesicles transformed to micelles as a result of the polarity difference between two azo isomers (cis and trans isomers). All of these transitions were found to be reversible. A new method to control the surface active/nonactive and vesicle/micelle transitions by light and pH has been established by introducing an azobenzene chromophore and GLBT into amphiphlic diblock copolymers.