Synthesis, photochemical properties, and self-assembly of diblock copolymer bearing azobenzene moieties

• An azobenzene-containing diblock copolymer was synthesized using sequential RAFT polymerization.
• The effects of azobenzene structure on E/Z photoisomerization, phase transition temperature, and self-assembly behavior of diblock copolymer were examined.
• Diblock copolymer showed lower E–Z photoisomerization rate (T1 = 68.0 s) compared with azo monomer (T1 = 10.95 s).
• Spherical aggregates of poly(StO50-b-Azo7) were obtained (approximately 181.4 nm) in a mixture of THF/H2O.

This study describes the synthesis of an azobenzene-containing diblock copolymer, poly(StO50-b-Azo7), by using the macro-chain transfer agent StO macro-CTA, and employing sequential reverse addition-fragmentation transfer (RAFT) polymerization. We studied the effects of azobenzene (azo) unit on E/Z photoisomerization, the phase transition temperature, and self-assembly behavior of diblock copolymer, and evaluated the characteristic time involved in the decay process of the photoisomerization kinetics of diblock copolymer. Diblock copolymer poly(StO50-b-Azo7) exhibited moderate thermal stability, with thermal decomposition temperature of 5% weight loss at approximately 340.9 °C, suggesting that the enhancement of the thermal stability was attributed to the incorporation of azo segments into block copolymer. The diblock copolymer showed lower E–Z photoisomerization rates (T1 = 68.0 s) compared with azo monomer (T1 = 10.95 s). Gradually adding water to the tetrahydrofuran (THF) solution of poly(StO50-b-Azo7) produced spherical micelles. Spherical aggregates of poly(StO50-b-Azo7) were obtained (mean diameter = approximately 181.4 nm) by diluting the polymer disperse in a mixture of THF/H2O (water content = 10 vol%), and are shown in TEM images of the diblock copolymer. The results of this study contribute to research on the development of photoresponsive polymer materials.