NMR spectra were measured with a Varian VNMR-S 500 MHz
spectrometer (Varian, Palo Alto, CA, USA) at 300 K using a 5 mm
inverse detection broadband probe. A total of 20 mg of polymer
was dissolved in 0.7 mL of CDCl3. Chemical shifts were given in
ppm relative to the remaining signals of chloroform as an internal