Amphiphilic Asymmetric Comb Copolymer with Pendant Pyrene Groups and PNIPAM Side Chains: Synthesis, Photophysical Properties, and Self-Assembly

Abstract

An amphiphilic asymmetric comb polymer with pendant pyrene groups and poly(N-isopropylacrylamide) (PNIPAM) side chains was synthesized based on click chemistry and reversible addition-fragmentation chain transfer polymerization. Gel permeation chromatography, FTIR, and (1)H NMR results all indicated successful synthesis of a well-defined comb polymer. The photophysical properties and self-assembly of the polymer in solution were studied by UV-vis spectroscopy, fluorescence technique, and transmission electron microscopy. The intensity ratio of the excimer peak (I(E)) to the monomer peak (I(M)) of the comb polymer in THF was used to monitor the formation of inter- or intramolecular excimers. At low polymer concentration, the value of I(E)/I(M) kept unchanged, indicating the formation of intramolecular excimer; at high polymer concentration, the value increased rapidly with concentration because of the formation of intermolecular excimer. The change of the intensity ratio of the first to the third vibronic band (I(1)/I(3)) on the monomer emission of the comb polymer also proved the association of the pendant pyrene groups in THF at high polymer concentration. In aqueous solution, the comb polymer chains self-assembled into vesicles with pyrene groups in the walls and PNIPAM side chains in the coronae. The value of the critical aggregation concentration of the polymer was determined by fluorescence technique. Temperature exerted a significant effect on the size and morphology of the vesicles. At a temperature above the lower critical solution temperature (LCST) of PNIPAM, PNIPAM brushes in the coronae of vesicles collapsed on the surface of the structures forming nanosized domains, and vesicles with smaller size were obtained. Fluorescence quenching experiments indicated that the collapsed PNIPAM chains protected a part of pyrene groups from being quenched by nitromethane at a temperature above the LCST of PNIPAM.

Post-polymerization modification reactions of poly(glycidyl methacrylate)s

“…In an alternative fashion, Zhao and co-workers showed that a small molecular acetylene appended with a RAFT agent can be attached to the azide group of the polymer and a subsequent RAFT polymerisation of NIPAM monomer could then lead to the gra copolymer structures (Scheme 14). 93 The formed secondary hydroxyl group could be subjected to an esterication reaction with a pyrene-based acid molecule. In aqueous solution, these polymers assembled into vesicular structures in which the hydrophilic NIPAM chains protected the hydrophobic pyrene groups.…”

Effects of graft length and density of well‐defined graft polymers on the thermoresponsive behavior and self‐assembly morphology

“…Zhao and coworkers reported the synthesis of an asymmetric macromolecular brush using PGMA as backbone and poly(ethylene glycol) not only as backbone but also as side chain as well as polystyrene and PNIPAM as side chains by ARTP, RAFT, and click method and investigated the morphology of aggregates of micelles and thermoresponsive behavior . They also prepared amphiphilic asymmetric comb polymer with pendant pyrene groups and two kinds of PNIPAM with different molecular weights as side chain by RAFT and click chemistry, and investigated the photophysical properties and self‐assembly behaviors of polymer in solution . Cai et al also reported a series of surface‐functionalized graft copolymer membrane with different molecular weight and a fixed graft density (8.85%) of PNIPAM and studied the temperature‐dependent flux of microporous membranes .…”

Clickable polyurethanes based on s‐triazine ring containing aromatic diisocyanate bearing pendent alkyne group: Synthesis and postmodification

“…The fluorescence emission spectra of PU‐PEG2K‐Py showed peaks at 373, 393 nm, and a broad excimer peak at 477 nm which correspond to pyrene emission and excimer emission, respectively. The presence of excimer peaks in dilute polymer solutions confirmed intramolecular π–π stacking of pyrenyl moities which in turn supports covalent linking of pyrenyl groups by click reaction.…”