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The synthesis of a series of dual thermosensitive nonionic−ionic random copolymers with varying compositions by reversible addition−fragmentation chain transfer polymerization is described. These copolymers contain oligo(2-ethyl-2-oxazoline)acrylate (OEtOxA) and either triphenyl-4-vinylbenzylphosphonium chloride ([VBTP][Cl]) or 3-n-butyl-1-vinylimidazolium bromide ([VBuIm][Br]) ionic liquid (IL) units. The copolymers having low content of ionic poly(ionic liquid) (PIL)) segments show only lower critical solution temperature (LCST)-type phase transition with almost linear increase of their cloud points with increasing percentage of ionic PIL segments. Furthermore, LCST-type cloud points (T cL s) are found very sensitive and tunable with respect to the nature and concentration of halide ions (X − = Cl − , Br − , and I − ) and copolymer compositions. However, copolymers with high content of ionic PIL segments show both LCST-type followed by upper critical solution temperature (UCST)-type phase transitions in the presence of halide ions. Dual LCST-and UCST-type phase behaviors are prominent and repeatable for many heating/cooling cycles. Both types of cloud points are found to be sensitive to copolymer compositions, concentration, and nature and concentration of the halide ions. The phase behaviors of both types of copolymers with a very high ionic content (>90%) are exactly similar to that of P[VBTP] [Cl] or P [VBuIm][Br] homopolymers showing only UCST-type phase transition in the presence of halide ions. The inherent biocompatibility of the P(OEtOxA) segment along with the interesting dual thermoresponsiveness makes these copolymers highly suitable candidates for biomedical applications including drug delivery.

Perylene bisimides (PBIs) with high quantum yields and high chemical and photophysical stabilities are usually suffering from poor solubility in various solvents, including water, which restricts their use in biomedical and other applications. Thus, in this study, as-synthesized hydrophilic poly(1-vinylimidazole) (PVim) is introduced at both the imide positions of the hydrophobic PBI unit by using L-cysteine (Cys) bearing two orthogonally reactive groups to produce a water-and organicsoluble PBI-based polymer conjugate. To do so, first, L-cysteine is used for thiol-mediated radical polymerization of 1-vinylimidazole (Vim). In the next step, the cysteine-end-capped poly(1-vinylimidazole) (Cys−PVim) with free −NH 2 is coupled with perylene-3,4,9,10-tetracarboxylic dianhydride (PDA) by employing a onestep microwave-assisted reaction to produce PBI−(Cys−PVim) 2 conjugate. The solution optical properties of this conjugate are thoroughly investigated to ascertain the extent of aggregation among PBIs units in both aqueous and organic media. The aqueous PBI−(Cys−PVim) 2 solution emits characteristic green fluorescence of PBI under UV irradiation of 365 nm wavelength. Owing to the presence of a protonable imidazole moiety, the PBI−(Cys−PVim) 2 conjugate shows pH-dependent optical properties. The amphiphilic PBI−(Cys−PVim) 2 molecules undergo self-assembly into vesicular nanostructures in water as confirmed from cryo-and high-resolution-transmission electron microscopy. The conjugate binds with ctDNA and plasmid DNA in water to form polyplexes. The fluorescent PBI−(Cys−PVim) 2 conjugate with low cytotoxicity and high quantum yield is efficiently used for the imaging of HeLa cells. The cellular uptake of the conjugate is studied at different time intervals and at different pHs using fluorescence microscopy.

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