Preparation and characterization of dual-responsive spiropyran-based random copolymer brushes via surface-initiated atom transfer radical polymerization

Silica nanoparticles (SiO₂) were grafted with the precursor random copolymer of 1′-(2-acryloxyethyl)-3′,3′-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2′-indoline) (SPMA) and tert-butyl methacrylate (tBMA) by surface-initiated atom transfer radical polymerization (SI-ATRP), and SiO₂-g-P(SPMA-co-methacrylic acid (MAA)) was obtained via chemical hydrolysis of the resulting precursor random copolymer in acidic conditions. From transmission electron microscopy, we observed the spherical morphology of monodispersed silica nanoparticles and core-shell structure of SiO₂-g-P(SPMA-co-MAA). Energy dispersive spectroscopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, and the thermogravimetric analysis indicated that the polymer had been successfully grafted onto the surface of silica nanoparticles. The dual-responsive properties were characterized by means of ultraviolet-visible spectrophotometer and dynamic light scattering. The average hydrodynamic diameter of SiO₂-g-P(SPMA-co-MAA) increased from 185.7 to 212.7 nm under ultraviolet light irradiation for 5 min. Also, the particle size of SiO₂-g-P(SPMA-co-MAA) increased with the rising pH value of surrounding condition.

采用表面引发原子转移自由基聚合（surface-initiated atom transfer radical polymerization, SI-ATRP）方法，将1′-(2-丙烯酰氧基乙基)-3′,3′-二甲基-6-硝基螺-(2H-1-苯并吡喃-2,2′-吲哚啉)（1′-(2-acryloxyethyl)-3′,3′-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2′-indoline), SPMA）与甲基丙烯酸叔丁酯（tert-butyl methacrylate, tBMA）的无规共聚前驱体接枝至二氧化硅（SiO₂）纳米颗粒表面；随后将所得前驱体无规共聚物在酸性条件下进行化学水解，得到SiO₂-g-P(SPMA-co-甲基丙烯酸（methacrylic acid, MAA）)。通过透射电子显微镜（transmission electron microscopy, TEM）观察到，单分散二氧化硅纳米颗粒呈球形形貌，且SiO₂-g-P(SPMA-co-MAA)具有核壳结构。能量色散光谱（energy dispersive spectroscopy, EDS）、傅里叶变换红外光谱（Fourier transform infrared spectra, FTIR）、X射线光电子能谱（X-ray photoelectron spectroscopy, XPS）以及热重分析（thermogravimetric analysis, TGA）结果证实，聚合物已成功接枝至二氧化硅纳米颗粒表面。采用紫外-可见分光光度计（ultraviolet-visible spectrophotometer, UV-Vis）与动态光散射（dynamic light scattering, DLS）表征了该材料的双重响应性能：经5 min紫外光辐照后，SiO₂-g-P(SPMA-co-MAA)的平均流体力学直径从185.7 nm增至212.7 nm；同时其粒径随周围环境pH值升高而增大。