*2.2. Synthesis of Polymers*

PIPOx was synthesized by a free-radical polymerization in bulk initiated by azobisisobutyronitrile (AIBN) as described elsewhere [18]. Molar mass of PIPOx was equal to 21,000 g/mol and Ð = 1.85. For 1H nuclear magnetic resonance (NMR) and Fouriertransform infrared spectroscopy (FTIR) spectra of PIPOx see Figures S1 and S2 in Supplementary Material.

PIPOx labeled with FITC (PIPOx-FITC) was prepared from PIPOx by two-step synthesis. In the first step, PIPOx (0.22 g, 0.001 mol of structural units) and ABA (0.020 g, 0.0002 mol) were dissolved in dry DMAc (1 mL) and heated at 120 ◦C for 6 h under argon. Reaction mixture was cooled, diluted with 5 mL of water, dialyzed towards deionized water (dialysis membrane Spectra/Por 6, Molecular weight cut-off (MWCO) 3.5 kDa, Spectrum Laboratories, Rancho Dominguez, CA, USA) for 4 × 1.5 h, and freeze-dried. Yield of reaction was 95% of PIPOx containing ABA (PIPOx-ABA). The chemical structure was determined from FTIR and NMR (Figures S3 and S2 in Supplementary Material). Prepared intermediate was functionalized with FITC using a standard protocol for labeling proteins. Briefly, 23 mg of PIPOx-ABA was dissolved in 0.1 M bicarbonate buffer (10 mL, pH = 9) and 1.6 mL of FITC in DMSO (1 mg/mL) was dropwise added for 5 min. Reaction mixture was held in 2–8 ◦C for 8 h under argon and product was purified using dialysis toward distilled water (dialysis membrane Spectra/Por 6, MWCO 3.5 kDa, Spectrum Laboratories, Rancho Dominguez, CA, USA). Yield: ~100%. The chemical structure was evaluated using 1H NMR and FTIR (Figures S4 and S2 in Supplementary Material), and degree of addition was calculated from UV/Vis absorption spectroscopy (Figure S5 in Supplementary Material).

#### *2.3. Analytical Methods*

The 1H and 13C NMR spectra for all polymers were conducted in CDCl3 and DMSO-d6 at room temperature using a Varian VXR-400 (Wilmington, DE, USA). In all measurements, tetramethylsilane was used as an internal standard. ATR-FTIR spectra of polymers were conducted by NICOLET 8700 (Thermo Scientific, Madison, WI, USA) using a Ge crystal with 64 scans and in resolution of 4 cm<sup>−</sup>1.

The molar mass and dispersity of PIPOx was recorded using size exclusion chromatography (SEC) as described elsewhere [18].

The UV/VIS spectra were recorded using Shimadzu 1650 PC (Shimadzu, Kyoto, Japan) in methanol at the concentration of 0.1 mg/mL for labeled polymers in the range of 210 to 600 nm in the resolution of 0.2 nm. The emission spectra were recorded on a Shimadzu RF-5301 (Shimadzu, Kyoto, Japan) in methanol using concentration ranged from 0.01 to 0.1 mg/mL with excitation wavelength of 495 nm.
