Abstract
Two poly(2-(dimethylamino)ethyl methacrylate)-b-poly(acrylic acid) diblock copolymers, PDMAEMA 84-b-PAA 18 and PDMAEMA 50-b-PAA 18, were synthesized by the atom transfer radical polymerization (ATRP) and their dual-stimuli responsive behaviors to the changes in temperature and pH in aqueous solutions were investigated by UV–vis spectroscopy, dynamic light scattering (DLS), 1H NMR spectroscopy and surface tension measurement. Different from PDMAEMA 84-b-PAA 18 solutions where no aggregation is observed between pH 7.0 and 9.5, the PDMAEMA 50-b-PAA 18 aggregates can exist in this broad pH range due to the hydrophobic interactions among the charge-balanced polyampholyte chains. At high pH, e.g., 11.0, the DMAEMA segments collapse to form the core of micelles due to the hydrophobic property of the de-protonized DMAEMA stabilized with the highly ionized AA segments on the surface of the micelles upon heating. At pH around the IEP, e.g., 9.5, large micelles can be formed in PDMAEMA 84-b-PAA 18 solution upon heating, just like that at pH 11.0, while PDMAEMA 50-b-PAA 18 first formed the micelles due to the electrostatic attraction between ionized AA segments and protonated DMAEMA segments, but the aggregation of the micelles was hardly happened upon heating due to the smaller DMAEMA segment. Moreover, LCST can be exactly estimated by surface tension experiment.
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