Abstract
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.
Highlights
Azobenzene-containing polymers have attracted much attention because they exhibit unique photo-responsive characteristics, such as photoisomerization, photochemical phase transitions, photoalignment and so on.[1,2,3,4] Their photo-responsive behavior depend on the chemical structures of azobenzene chromophore groups, and on their organization in the polymer matrix
The gra block copolymer poly[6-(4-methoxy-azobenzene-40oxy)hexyl methacrylate] (PAzoMA)-b-(PELG-g-MPEG) was synthesized by click chemistry according to the literature.[48]
The obtained results from 1H NMR, FTIR and gel permeation chromatograph (GPC) demonstrated that the alkyne-PAzoMA59 precursor was successfully synthesized by atom transfer radical polymerization (ATRP)
Summary
Azobenzene-containing polymers (i.e. azo-polymers) have attracted much attention because they exhibit unique photo-responsive characteristics, such as photoisomerization, photochemical phase transitions, photoalignment and so on.[1,2,3,4] Their photo-responsive behavior depend on the chemical structures of azobenzene chromophore groups, and on their organization in the polymer matrix. The gra block copolymer PAzoMA-b-(PELG-g-MPEG) was synthesized by click chemistry according to the literature.[48] Typically, PAzoMA59-b-PAELG50 (0.35 g, 0.53 mmol of azido groups), alkyne-MPEG (1.86 g, 5.3 mmol), CuBr (0.76 g, 5.3 mmol) and PMDETA (0.89 g, 5.3 mmol) were dissolved in 10 mL DMF at a Schlenk tube. The gra block copolymer PAzoMA-b(PELG-g-MPEG) was synthesized by the combination of ATRP, ROP and click reaction.
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