A pH and redox dual responsive homopolypeptide: synthesis, characterization, and application in "smart" single-walled carbon nanotube dispersionElectronic supplementary information (ESI) available: GPC chromatograph of PMCELC (Fig. S1) and PCELC (Fig. S3), 1H NMR spectra of PMCELC in DMSO-d6 and PCELC in D2O for the calculation of DPNMR (Fig. S2), pH titration curve of PCELC (Fig. S4), optical images (Fig. S5) and DLS size distribution plots (Fig. S6) of PCELCox and PCELCre aqueous solutions wit

A homopolypeptide, namely poly( S -(2-carboxylethyl)- l -cysteine) (PCELC), with pH and redox dual responsiveness was prepared by ring-opening polymerization of S -(2-(methoxycarbonyl)ethyl)- l -cysteine based N -carboxyanhydride (MCELC-NCA) and subsequent hydrolysis. The pH-induced solution phase transition of PCELC was at pH = ∼4.50 as revealed by DLS and UV-vis spectroscopy. The thioether linkages of PCELC can be readily oxidized by H 2 O 2 at 40 °C yielding PCELC ox with sulfoxide and sulfone linkages as revealed by 1 H NMR and FTIR. PCELC ox also showed pH responsiveness with the variation of polymer aggregation sizes, but without solution phase separation. PCELC ox can be partially reduced by 3-mercaptopropionic acid as suggested by 1 H NMR and FTIR analysis. The pH-induced solution phase transition behavior of the reduction product ( i.e. , PCELC re ) was different from that of the as-prepared PCELC. Moreover, PCELC can be used as a pH and oxidation dual responsive stabilizer to control the aggregation of single-walled carbon nanotubes (SWCNTs) in aqueous solution. We present the synthesis and characterization of a pH and redox dual responsive homopolypeptide which can be used as a dual responsive stabilizer to control the aggregation of carbon nanotubes in water.