Synthesis And Stimuli Responsive Behaviors Of PDMAEMA-based Diblock Copolymers In Aqueous Solutions

Stimuli-responsive block copolymers, as a new class of "smart" materials, due to their tunable physical and chemical properties by external stimuli, are taken more and more attention in practical applications. In this work, A series of poly(N,N-dimethylaminoethyl methacrylate)(PDMAEMA)-based diblock copolymers were synthesized, and the structural characterization, their stimuli-responsive properties and application in gene delivery were investigated.PDMAEMA-based diblock copolymer were successfully synthesized by atomic transfer radical polymerization using ethyl2-bromoisobutyrate or bromide-terminated macroinitiator as an initiator and Cu’Br/PMDETA as the catalyst system. The structural characterization of the PDMAEMA-based diblock copolymer were studied by]H NMR, GPC and FT-IR.The temperature-and pH-responsive behavior of PDMAEMA-b-PAA and mPEG-b-PDMAEMA diblock copolymers in aqueous solutions and the evolution of this process were investigated through a combined approach of surface tension measurement, UV-vis spectroscopy, dynamic light scattering (DLS) and H NMR spectroscopy. There are hystereses of aggregation and dissolution profiles for these diblock copolymers, and the hysteresis is higher for the copolymer with longer chain length. For acidic solution, no aggregation is observed upon heating, due to the protonized PDMAEMA block and the hydrophilic PAA block and PEG block. At high pH, PDMAEMA-b-PAA diblock copolymer lead to an increasing tendency to form micellar aggregates upon heating, which can be adjusted by varying the molecular weight and composition of the PDMAEMA-b-PAA block copolymers. A significant difference of the stimuli-responsive behavior between PDMAEMA-rich and PAA-rich copolymers is observed where the former one exhibits thermo-responsive behavior in a broad temperature range of40-60℃in basic media, while the pH-responsive behavior is dominant and only a weak thermo-responsive behavior exhibits around the specific isoelectric point (IEP) in the latter case. The mPEG-b-PDMAEMA diblock copolymer exhibited an unusual thermally induced two-stage aggregation process at alkaline solution. With a specific copolymer composition, mPEG-b-PDMAEMA copolymer showed a unique tunable phase transition from no-responsiveness in acid media to an S-I transition in neutral media and an S-I-S transition in basic media either in presence of salt or for salt-free solutions. The copolymer chains associate at the first thermal transition followed by a rearrangement process at the second thermal transition to produce a stable core-shell micellar structure.Simply mixing the PDMAEMA-based polycation with DNA in aqueous buffer solution produces electrostatic complexes between DNA and polycation that have well-defined and charge characteristics. DLS and Agarose gel electrophoresis measurements indicate that the PDMAEMA-based polyplexes show good performance and exhibit greater stability against disintegration induced by polyanionic additives.