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.