Amphiphilic Diblock Copolymers Functionalized with Strong Push−Pull Azo Chromophores: Synthesis and Multi-Morphological Aggregation

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Abstract

This article reports the synthesis, characterization, and multimorphological aggregation of a series of amphiphilic diblock copolymers bearing strong push−pull azo chromophores. The diblock copolymers (PEGx-b-PCNy), which consist of poly(ethylene glycol) (PEG) and 2-(N-ethyl-N-(4-(4′-cyanophenylazo)phenyl)amino)ethyl methacrylate (PCN) blocks, were synthesized through atom transfer radical polymerization (ATRP) and postpolymerization azo-coupling reaction. PEGx-b-PCNy was prepared to have different hydrophilic/hydrophobic ratios (x = 122, y = 24, 62, 129, 224). Self-assembled aggregates were formed by the gradual addition of water to the solutions of the copolymers in THF. The formation process and morphology of the aggregates were characterized by DLS, SLS, SEM, and TEM. Results show that the block polymers start to form aggregates at the critical water content (CWC), which is related to the initial polymer concentration in THF and PCN block length. The morphology of the aggregates formed in the solutions is controlled by the PCN block length and preparation conditions. With the increase in the PCN length, the aggregates show different morphologies such as spherical micelles, rodlike aggregates, hollow nanotubes, and colloidal spheres. In the experimental range, a change in the polymer initial concentration in THF does not show an obvious effect on the aggregate morphology. The water-adding rate in the preparation process shows an important effect on the aggregate morphology. When the water-adding rate increases from 0.5 to 7.2 mL/h, the morphology of PEG122-b-PCN129 aggregates changes from nanotubes to a mixture of giant vesicles and colloidal spheres. Some well-organized aggregates developed from the photoresponsive copolymers could have potential applications in photocontrollable drug delivery and other uses.

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