We report the formation of cylindrical micelles, sheet-like micelles, tubular micelles, as well as polymer vesicles by a new series of amphiphilic linear-dendritic block-copolymers (BCs). The BCs, noted as PEGm-AZOn, are composed of poly(ethylene glycol) (PEG) chains of different molecular weights as hydrophilic blocks and the first four generations of azobenzene-containing dendrons based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) as hydrophobic blocks (m represents the degree of polymerization of PEG, and n is the number of azobenzene units at the periphery of dendron). The polymeric aggregates were formed by adding water to solutions of the BCs in dioxane. The micellar dispersions in water were finally obtained by removing dioxane via dialysis against water. The morphology of the micellar self-assemblies was studied by transmission electron microscopy (TEM), cryo-electron microscopy (cryo-TEM), and atomic force microscopy (AFM). A generation-dependent aggregation behavior was found for the series of BCs PEG45-AZOn. Core-shell structured nanofibers with an inner diameter of 8 nm were observed for the copolymer PEG45-AZO2 (hydrophilic/hydrophobic weight ratio equal to 67/33). Lyotropic liquid crystalline behavior was detected for the aqueous solution of the nanofibers. The coexistence of sheet-like aggregates and tubular micelles was detected for the copolymer PEG45-AZO8 in which the number of cyanoazobenzene units is increased to 8 (hydrophilic/hydrophobic weight ratio equal to 33/67). The tubular micelles could be intermediates in the sheet-like aggregate-to-vesicle transition. Polymer vesicles (polymersomes) with a diameter in the range 300-800 nm were observed for the copolymer PEG45-AZO16 (hydrophilic/hydrophobic weight ratio equal to 20/80). The membrane of the sheet-like aggregates, tubular micelles, and polymersomes was shown to have a bilayer structure, as revealed by cryo-TEM. UV illumination of the aqueous polymersome dispersion induced the formation of wrinkles in the vesicle membrane, thus showing that this type of polymeric aggregate is photoresponsive.

We report the synthesis and characterization of a novel azobenzene-containing miktoarm star polymer AB 3 (M n = 9700 g mol −1 , Đ M = 1.10) as well as its self-assembly properties in water. The miktoarm copolymer is composed of a hydrophobic azopolymer and three hydrophilic PEG arms (M n = 600 g mol −1 ). The hydrophobic/hydrophilic ratio of the amphiphilic miktoarm polymer is 78/22, leading to the formation of stable polymeric vesicles in water evidenced via TEM and cryo-TEM imaging. The photoresponse of these vesicles has been investigated by irradiation with UV light (λ = 350−400 nm) causing the disruption of the self-assemblies. Encapsulation of both hydrophilic and hydrophobic fluorescent probes, i.e., Nile Red and Rhodamine B, and the use of light as an external stimulus to trigger the release of the probes have also been demonstrated.

We report on the synthesis and characterization of a series of amphiphilic linear–dendritic block copolymers (LDBCs) as well as their self-assembly in water. The LDBCs are composed of a 2000 g/mol poly(ethylene glycol) (PEG) linear segment linked to the fourth generation of a 2,2-di(hydroxymethyl)propionic acid (bis-MPA)-based dendron containing 4-isobutyloxyazobenzene units (AZO) and hydrocarbon chains (C18) randomly connected to the periphery of the dendron. TEM and cryo-TEM images show that all the LDBCs form stable vesicles in water. The influence of AZO/C18 ratio in the photoresponse of the self-assemblies has been assessed as well as the encapsulation of both hydrophilic (Rhodamine B) and hydrophobic (Nile Red) fluorescent probes and the use of light as an external stimulus to trigger the release of the probes. The results show that by diluting the azobenzene content at the periphery of the dendron, the trans-to-cis photoisomerization rate can be substantially accelerated and the light-induced release activity can be tuned being the vesicles with a 50/50 AZO/C18 ratio the ones suffering the most significant changes upon irradiation.