Synthesis of thermo-responsive block copolymers of random copolymer blocks allows the tuning of the phase transition temperatures of individual blocks and the introduction of multiple cloud points for a single polymer in water. The same technique can be applied for other stimuli. Diblock random copolymers with dual stimuli-responsive blocks have been designed and synthesized via a sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. A well-defined block copolymer in the form of AnBm-b-ApCq, was prepared where A, B and C are N-n-propylacrylamide (nPA), 2-(diethylamino)ethyl methacrylate (DEAEMA) and N-ethylacrylamide (EA), respectively. This polymer shows interesting �schizophrenic� behaviors in aqueous solutions.Both random copolymer blocks are thermo-responsive and one block is also pH-responsive since the tertiary amine group of DEAEMA becomes protonated at a lower pH. The block copolymers can be molecularly dissolved in water at 25 oC (pH 7), self-assembling to form vesicles with poly(nPA0.8-co-EA0.2) as the hydrophobic membrane inner layer at 37 oC (pH 7), while the inner and outer layers may be switched at 25 oC (pH 10). The random nature of the blocks allows the fine-tuning of their thermo-responsiveness. In addition, the copolymers manifest stepwise responsiveness in both alkaline and neutral media corresponding to the cloud points of the individual blocks. Solution behavior and nanoparticle morphologies have been studied with 1H-NMR, DLS, SLS, zeta potential measurements, as well as imaging techniques, including AFM and TEM.

Invertible nanostructures formed by stimuli-responsive diblock random copolymers

248th National Meeting (2014)

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