In order to study the kinetics of photo-induced ring-opening, the UVeVIS spectra of amphiphilic copolymer P(SPMA-co-MAA) under the irradiation of ultraviolet light (365 nm) at different times are recorded.
As can be seen from Fig. 4, the absorbance at lmax 1⁄4 551 nm of P(SPMA-co-MAA) in THF increases with the extension of illumination time.
After UV irradiation for 300 s, the absorbance at lmax keeps almost constant with the prolonging irradiation time, implying that the conversion from SP to MC has been balanced.
The ring-closure from MC to SP is thermally induced upon removal of the UV light resource. The solution of P(SPMA-co-MAA) in THF (3.3 10$2 wt%) is exposed to UV light source for 300 s and the UVeVIS spectra is recorded immediately.
The sample is placed in an oil bath for different times at 45 C and the spectrum is taken directly.
Fig. 5 shows that the absorbance at lmax decreases abruptly with the prolonging of heating time.
When heating time is more than 100 s, the UVeVIS curve attains a stable plateau as demon- strated in Fig. 5 inset, manifesting the formation of isomerization balance.