Photoresponsive Dendronized Copolymers of Styrene and Maleic Anhydride Pendant with Poly(amidoamine) Dendrons as Side Groups
journal contributionposted on 12.03.2013, 00:00 by Zhijian Wang, Min Gao, Jianbo Sun, Dehai Liang, Xinru Jia
A series of photoresponsive dendronized polymers PGn-NB (n = 1, 2, 3) were synthesized by attaching o-nitrobenzyl alcohol-terminated amidoamine dendrons (G1–G3) to the alternating styrene and maleic anhydride copolymer (PSt-alt-PMAh). The structures and the molecular weights of the obtained polymers were characterized by 1H NMR and FTIR measurements. It is found that the coverage degrees of the dendrons are 74%, 42%, and 26%, respectively, indicating that the numbers of the appended dendrons decrease in the order of G1 > G2 > G3 due to the steric hindrance of higher generation dendrons with more branches. The photocleavable behavior of G1–G3 was detected by UV–vis and 1H NMR measurements. As a result, G2 showed a faster cleavage rate compared to G1 and G3. The critical aggregation concentration (CAC) of PGn-NB (n = 1, 2, 3), measured by using pyrene as a fluorescence probe, were 0.05 mg/mL (PG1-NB), 0.01 mg/mL (PG2-NB), and 0.03 mg/mL (PG3-NB), which displayed that the structure of PG2-NB was in favor of forming aggregates at lower concentrations. Light scattering study indicated that both the apparent molecular weight and the chain density of the aggregates formed by PG2-NB decreased with the irradiation time. Atomic force microscope (AFM) measurements also showed that the size of the aggregates increased dramatically from 15 to 70 nm before and after UV irradiation, evidencing that the UV light induced structure change. Nile Reds, as the guest molecules, were loaded in the aggregates from PG2-NB, and the release profiles upon UV stimulus were monitored by the fluorescence spectroscopy.