Self-Organization of Macromolecules of Block Copolymers of Poly-2-alkyl-5,6-dihydrooxazines in Aqueous and Water–Salt Solutions

Abstract

Block copolymers of poly-2-ethyl- and poly-2-isopropyl-5,6-dihydrooxazines with different sequences of blocks relative to the terminal groups are synthesized by cationic ring-opening polymerization. It is shown by nuclear magnetic resonance (NMR) spectroscopy that the fraction of poly-2-ethyl-5,6-dihydrooxazine monomers in the copolymers is 61 and 65%. The molecular weights of the samples are 2200 and 3300 g/mol. Upon heating aqueous and water–salt solutions of block copolymers, a phase transition with the formation of supramolecular structures is found by light scattering and turbidimetry. The lower critical solution temperature (LCST) of the block copolymers is below the LCST of the more hydrophilic poly-2-ethyl-5,6-dihydrooxazine and above the LCST of the more hydrophobic poly-2-isopropyl-5,6-dihydrooxazine. An increase in the fraction of units of the latter leads to a decrease in the LCST. The addition of NaCl to solutions of copolymers induces an insignificant decrease in the temperature of phase separation.