Synthesis and characterization of side-chain liquid crystalline ABC triblock copolymers withp-methoxyazobenzene moieties by atom transfer radical polymerization

Novel amphiphilic graft block azobenzene-containing copolymer with polypeptide block: synthesis, self-assembly and photo-responsive behavior

Well-defined amphiphilic graft block azobenzene-containing copolymer with polypeptide block was synthesized via a combination of copper-mediated atom transfer radical polymerization (ATRP), ring-opening polymerization and click reaction. The alkyne-terminated poly[6-(4-methoxy-azobenzene-4′-oxy)hexyl methacrylate] (PAzoMA) was synthesized by ATRP with a bromine-containing alkyne bifunctional initiator, and the azido-terminated poly(γ-2-chloroethyl-l-glutamate) (PCELG) was synthesized by ROP of γ-2-chloroethyl-l-glutamate-N-carboxyanhydride (CELG-NCA), then the two homopolymers were conjugated by click reaction to afford block azobenzene-containing copolymer PAzoMA-b-PCELG. The chloro groups in PCELG block were transformed into azido groups via azide reactions, and the alkyne-terminated MPEG was grafted to the polypeptide block to afford the final product PAzoMA-b-poly((l-glutamate)-graft-methoxy poly(ethylene glycol)) (PAzoMA-b-(PELG-g-MPEG)) by click reaction. Giant vesicles (micrometer size) were obtained from the amphiphilic graft block copolymer PAzoMA-b-(PELG-g-MPEG) through a solution self-assembly due to the rigid PAzoMA chains and polypeptide chains with the α-helical structure. The investigation of the photo-isomerization behavior of PAzoMA-b-(PELG-g-MPEG) in solution and in vesicular solution showed trans–cis isomerization in solution was quicker than that in vesicular solution and azobenzene J-aggregates in the vesicle solution were only observed. The formation mechanisms of the vesicles were also explored. The research results may provide guidelines for the study of complex copolymers containing different types of rigid chains.

Giant vesicles (micrometer size) were prepared from novel amphiphilic graft block azobenzene-containing copolymer with polypeptide block synthesized via a combination of ATRP, ROP and click reaction.

Synthesis and characteristics of novel azo-based diblock copolymers and their self-assembly behavior via solvents and thermal annealing

A series of azo-based diblock copolymers (DBCs) with various compositions were successfully synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization in anisole with PCAEMA-CTA (macro-CTA), DOPAM (new acrylamide monomer) and AIBN (initiator). Kinetic studies on diblock copolymerization manifested a controlled/living manner with good molecular weight control. Structures and properties of monomers and DBCs were determined by 1H nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). Liquid crystalline (LC) phases and morphological properties were investigated using optical polarizing microscope (OPM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS). Experimental results demonstrated that the prepared PCAEMA-CTA and DBCs possessed low polydispersity index (≤1.37). All DBCs revealed sharp endothermic transition peaks corresponding to the smectic-to-nematic phase. DBCs with high azo contents showed batonnet textures of the smectic phase whereas DBCs of low azo segments displayed threaded textures of the nematic phase. DBC with 49 wt% of azo side-chains generated a lamellar compared to DBCs with low azo block (≤41 wt%) or non-azo block (≤38 wt%) which produced hexagonal-type nanostructures. In addition, all DBCs exhibited reversible trans-cis photoisomerization behavior under UV irradiation and dark storage at different intervals of time.

Polymeric micelles stabilized by polyethylenimine–copper (C2H5N–Cu) coordination for sustained drug release

Polymeric micelles stabilized by polyethylenimine–copper (C₂H₅N–Cu) coordination were described to improve the release property of water-insoluble anticancer drug.

Tuning self-assembly and photo-responsive behavior of azobenzene-containing triblock copolymers by combining homopolymers

The self-assembly behavior of azobenzene-based triblock copolymers poly(ethylene oxide)-block-polystyrene-block-poly[6-(4-methoxy-4'-oxy-azobenzene) hexyl methacrylate] (PEO-b-PS-b-PMMAZO) and their mixtures with PS or PMMAZO homopolymers was studied by means of transmission electron microscopy, scanning electron microscopy, laser light scattering and UV-vis spectrophotometry. It was found that pure block copolymers self-assembled into spherical micelles with core-shell structures. The addition of PS or PMMAZO homopolymers can not only increase the aggregate size but also have a significant influence on the photo-isomerization behavior and photo-deformation behavior of the aggregate. The photo-isomerization study revealed that a complete trans-cis or cis-trans isomerization of azobenzene chromophores can be acquired when irradiated with UV or visible light for polymers both in organic solutions and in micelles. The photo-isomerization rate of azobenzene chromophores increases when PS homopolymers were incorporated into micelles, while with the addition of PMMAZO homopolymers, it decreases. The photo-induced elongation of the aggregates by irradiation of a linearly polarized laser was observed for all the samples, and the deformation degree increases with the weight fraction of azobenzene groups in the parent copolymers, as well as the PMMAZO content for the mixture micelles.