The structure and composition of random copolymers were determined by 1H NMR (Bruker AVANCE III 500 MHz) using CDCl3 as solvent containing tetramethylsilane which serves as internal reference.
The molecular weight and distribution of the copolymers were determined by Gel Permeation Chromatography (GPC, Waters 515). THF was the mobile phase which delivered at a rate of 1 mL/min, and commercially available PMMA sample with a narrow molecular distribution was used as the standard to generate a calibration curve.
Fourier Transform Infrared Spectroscopy (FT-IR) measurements were taken with a Nicolet model 6700 in the spectral region from 450 to 4000 cm$1.
The solvatochromism of amphiphilic random copolymers in different solvents were recorded on UV-2450 Spectrometer in the spectra region from 200 to 800 nm. The concentration of the
copolymers was 3.3 10$2 wt%.
The UVeVIS spectra of the polymers before and after hydrolysis were taken at the same time. The kinetic curves of the isomerization between SP and MC were recorded by monitoring the absorbance at maximum wavelength (lmax).
The influence of acid or base on the equilibrium between SP and MC had been investigated.
A 3.3 10$2 wt% aqueous solution of P(SPMA-co-MAA) was prepared by adding 1 mg sample to 3 mL deionized water (pH 1⁄4 12).
The spectra were taken after adding 2.4 mL aliquots of 0.1 mol/L HCl or 1 mol/L NaOH solution.
The reversible complexation behavior of MC and divalent metal ions was also recorded on UVeVIS spectra, and the typical process was as follows [33]: 2.9 mL P(SPMA-co-MAA) solution in THF (3.998 10$2 wt%) was irradiated under visible light (250 w) for 1 min to ensure full ring-closure of spiropyran and the absorption spectrum was taken.
Then the solution was illuminated for 6 min using the UV source of wavelength 365 nm (12 w) and the absorbance spectrum was recorded immediately after illumination.
After that, the solution was spiked with 100 mL divalent metal chloride solution in THF (2 mmol/L) and illuminated for 1 min under UV light, and the spectrum was then determined. In order to investigate the reversibility, the solution (still containing divalent metal ions) was irradiated with visible light for 1 min and the spectrum was taken.
Finally, the solution was illuminated with UV light for 6 min and the spectrum recorded.