Block co-polymers undergoing supra-molecular association

A thermo-sensitive ionic block copolymer, PAMPTMA-b-PNIPAAM, made of poly (N-isopropylacrylamide), (PNIPAAM), and poly (3-acrylamido propyltrimethyl-ammonium chloride) (PAMPTMA) parts was synthesized. Its solution properties were investigated by viscosity, DLS and ζ-potential measurements. In solution the block co-polymer undergoes thermal transitions above a critical temperature, CMT, and forms micelles. The transition depends on the amount of added NaCl. A comparison of the performances below and above the CMT was made and related to the medium ionic strength, i.e. to the residual charges on PAMPTMA domains.Progressive shifts of the CMT to lower values is ascribed to the reduced repulsions between positive charges of PAMPTMA moieties, induced by added salt, and to the subsequent decrease of the lower critical solution temperature (LCST), of the block co-polymer. The LCST regularly decrease on increasing the added salt and can be properly modulated.The block-copolymer interacts electrostatically with oppositely charged poly-electrolytes. Preliminary studies indicate that, above the CMT, PNIPAAM/PAMPTMA binds to DNA, with formation of micelle/DNA complexes, macroscopic phase separation and precipitation, depending on the relative ratios. Care was devoted to find the experimental conditions compatible with body temperature, in view of possible use in DNA transfection technologies.

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► A new ionic block copolymer undergoes thermal transitions and forms micelles.
► The transition depends on the amount of added salt.
► The block-copolymer interacts electrostatically and binds to DNA.
► Complexes, macroscopic phase separation and/or precipitation occur with DNA.