Valerii N. Kizhnyaev

The possibility of using oxirane and imidazole rings as “anchor” functional groups in the structure of flexible-chain polymers for their reactive mixing has been demonstrated. It has been shown that the obligatory condition for the crosslinking of oxirane- and imidazole-containing polymers is the presence of water in the reaction system. Polymer networks formed similarly from linear water-soluble lactam- and imidazole-containing polymers form stimulus-sensitive hydrogels with ionic conductivity upon swelling in water.

Amphiphilic and polyelectrolyte crosslinked polymer products with different types of network structure capable of limited swelling in aqueous media to form hydrogels exhibiting pH-sensitive properties were synthesized by the interaction of tetrazole-containing polysaccharides with the epoxy resin and oxirane-containing carbon chain polymers.

Various bi- and polycyclic pyrimidine derivatives (including fused ones) containing different aza- and carbocyclic fragments have been synthesized via a modified Biginelli reaction.

Polymerization of 5-vinyltetrazole under conditions of radical initiation in aqueous media in the presence of chitosan gave network graft copolymers, the structure of which is built from chitosan macromolecules crosslinked by chain fragments of poly(5-vinyltetrazole). It was determined that the polymerization is preceded by the formation of a saltlike product between chitosan macromolecules and vinyl monomer, which affects its polymerization activity. The obtained graft copolymers are prone to limited swelling in water to form pH-sensitive ampholytic hydrogels.

Polymerization of 5-vinyltetrazole under conditions of radical initiation in aqueous media in the presence of chitosan gave network graft copolymers, the structure of which is built from chitosan macromolecules crosslinked by chain fragments of poly(5-vinyltetrazole). It was determined that the polymerization is preceded by the formation of a saltlike product between chitosan macromolecules and vinyl monomer, which affects its polymerization activity. The obtained graft copolymers are prone to limited swelling in water to form pH-sensitive ampholytic hydrogels.

The effect of low-molecular-weight salts (Na₂SO₄, KCl, NaF, and NaSCN) on swelling of poly-electrolyte and amphiphilic hydrogels of network paired polymers of poly-N-vinylpyrrolidone with poly-5-vinyltetrazole, polystyrene, and poly(methyl methacrylate) in aqueous media was demonstrated. It was shown that the amplitude and character of the collapse of the hydrogels are determined by the nature of the salt and of the macromolecules constituting the paired polymer.

The synthesis of tetrazole-containing derivatives of chitosan, starch, and arabinogalactan was carried out by a sequence of reactions including cyanoethylation of polysaccharides and subsequent azidation of cyanoethyl derivatives. The reaction of cyanoethylation of polysaccharides with acrylonitrile proceeds in the temperature range 40–60°C in the presence of NaOH. The transformation of nitrile groups into tetrazole rings (azidation) of cyanoethylated polysaccharide derivatives was carried out with a mixture of sodium azide with ammonium chloride in DMF at 105°C. The reaction with the participation of derivatives of starch and arabinogalactan is characterized by the degree of conversion of nitrile groups into tetrazole rings, which is close to the maximum. The introduction of unsubstituted tetrazole rings into the structure of polysaccharides of acidic N–H substantially changes some of their properties. Like other carbo- and hetero-chain polymers containing N–H unsubstituted tetrazole rings in the structure, tetrazolated polysaccharides exhibit the properties of acidic polyelectrolytes. Tetrazole-containing derivatives of chitosan exhibit the properties of polyampholytes. The presence of tetrazole rings in the structure of modified polysaccharides allows the reaction with epoxy compounds to yield network polymers capable of limited swelling in aqueous media with the formation of polyelectrolyte hydrogels.

T—The effect of pH, ionic strength, and ambient temperature on the behavior of hydrogels of network paired polymers synthesized by reactive blending of poly-N-vinylpyrrolidone and poly-N-vinylcaprolactam with poly-1-vinyl-3-amino-1,2,4-triazole is demonstrated. It is found that hydrophobic interactions of the fragments of the polymer chains have a major role in the changes of the sorption properties of the hydrogels in response to variation in the solvent properties.

In this work, we have proposed a novel universal stimulus-sensitive nanosized polymer system based on decasubstituted macrocyclic structures—pillar[5]arenes and tetrazole-containing polymers. Decasubstituted pillar[5]arenes containing a large, good leaving tosylate, and phthalimide groups were first synthesized and characterized. Pillar[5]arenes containing primary and tertiary amino groups, capable of interacting with tetrazole-containing polymers, were obtained with high yield by removing the tosylate and phthalimide protection. According to the fluorescence spectroscopy data, a dramatic fluorescence enhancement in the pillar[5]arene/fluorescein/polymer system was observed with decreasing pH from neutral (pH = 7) to acidic (pH = 5). This indicates the destruction of associates and the release of the dye at a pH close to 5. The presented results open a broad range of opportunities for the development of new universal stimulus-sensitive drug delivery systems containing macrocycles and nontoxic tetrazole-based polymers.