Acetic acid d4

¹H NMR spectra of the samples were recorded with a 400 MHz Bruker^®Avance III High Resolution spectrometer (Bruker BioSpin GmbH, Rheinstetten, Germany) using D₂O with acetic acid-d₄ (Sigma-Aldrich) as a solvent. The solutions (1% w/v) of CS, PNIPAAm and synthesized copolymer were prepared. Chemical shifts were reported in ppm using the signal of D₂O (4.79 ppm) as internal standard. To estimate the molar percentages of CS and NIPAAm in the copolymers, the ratio of the integration of the signal at 1.96 ppm corresponding to CS to that of the signal at 1.01 ppm corresponding to PNIPAAm side chains was used. The molar percentages of NIPAAm and CS were calculated as follows: $$\mathrm{NIPAAm}\%=\frac{\left( \frac{\mathrm{H}}{\mathrm{n}}·100\right)}{ \left( \frac{\mathrm{H}}{\mathrm{n}}\right)+\left( \frac{\mathrm{A}}{3}:0.24\right)}$$
$$\mathrm{CS}\%=100\%-\mathrm{NIPAAm}\%$$
where H is the peak area of the isopropyl group of NIPAAm in the grafted chain, n is the number of isopropyl group protons in NIPAAm, A is the peak area of the acetyl group signal, 3 is the number of acetyl group protons, and 0.24 is the degree of acetylation of CS.

Amino acids, N,N′-diisopropylethylamine (DIEA), N,N′-Disuccinimidyl carbonate (DSC), Fmoc chloride, (1-cyano-2-ethoxy-2-oxoethylidenaminooxy)dimethylamino-morpholino-carbenium hexafluorophosphate (COMU), chloro-N,N,N′,N′-tetramethylformamidinium hexafluorophospate (TCFH) and triphosgene (BTC) were purchased from Chem Impex Int’l, Inc. Reagents such as piperidine, lithium chloride, sodium cyanoborohydride (NaBH₃CN), triisopropylsilane (TIPS), sodium acetate-d₃, acetic acid-d₄, and D₂O were purchased from Sigma Aldrich. Reagents such as hydrazine monohydrate and 2,4,6-collidine were purchased from Alfa Aesar. Trifluoroacetic acid, glacial acetic acid, sodium bicarbonate, and solvents were purchased from Fisher. Reagents including HBTU and PyBOP were purchased from Oakwood Chemical. 1-Methylimidazole (NMI) and 1-chloro-N,N,2-trimethylpropenylamine (Ghosez’s Reagent) were purchased from Acros Organics.

The reference standards, including acetic acid (purity ≥ 99%), propionic acid (purity ≥ 99.5%), butyric acid (purity ≥ 99.5%), valeric acid (purity ≥ 99.8%), and acetic acid-d₄ (purity ≥ 99.5%) were obtained from Sigma-Aldrich (South Korea), and the butyric acid-d₇ (purity ≥ 98%) was obtained from Cayman Chemical (Ann Arbor, MI, USA).
The reagents, including 37% HCl, MTBE (purity ≥ 99.5%), DE (purity ≥ 99.9%), chloroform (Chl, purity ≥ 99.5%), n-hexane (HA, purity ≥ 95%), bovine serum albumin (BSA), phosphate buffer saline (1.0 M), and dextran-coated charcoal were obtained from Sigma-Aldrich (Darmstadt, Germany), and distilled water was obtained from J. T. Baker (Phillipsburg, NJ, USA).