Thermo- and pH-Responsive Dendronized Copolymers of Styrene and Maleic Anhydride Pendant with Poly(amidoamine) Dendrons as Side Groups

A series of thermo- and pH-dual responsive dendronized polymers PSADG1−PSADG3 were successfully synthesized by attaching butylamide terminated poly(amidoamine) dendrons (DG1−DG3) to the alternating copolymers of styrene (St) and maleic anhydride (MAh). The structures and the molecular weights of the obtained polymers were characterized by 1H NMR and FTIR. The coverage degrees of DG1−DG3 dendrons were 83.5%, 64.9%, and 60.5%, respectively, indicating that the numbers of the attaching dendrons decreased in the order of G1 > G2 > G3. The turbidity measurements revealed that all the dendronized polymers exhibited reversible thermo-responsive property in deionized water, and the LCST values increased from PSADG1 to PSADG3 due to both the coverage degree and the structure of dendrons. Moreover, these dendronized polymers were sensitive to pH on account of the carboxylic and tertiary amino groups in the architecture. It has been found that, for example, the PSADG2 did not display thermal sensitivity in acidic environment (pH 2.4), whereas the phase transition occurred in near neutral (pH 6.0) and basic conditions (pH 10.6) with the LCST of 33.1 and 49.0 °C, respectively. It was also found that, at pH 6.0, the polymers formed larger aggregates with Rh,app of ca. 0.6 μm at elevated temperatures mainly because of the dehydration and the enhanced hydrophobic interactions. The morphology of the aggregates was monitored by optical microscopy, and uniform spherical aggregates with a diameter of 5−10 μm were observed above the LCST.