Cryostructuring of polymeric systems. 38. The causes of the covalently-crosslinked cryogels formation upon the homopolymerization of N,N-dimethylacrylamide in moderately-frozen aqueous media

Abstract

The redox-initiated homopolymerization of N,N-dimethylacrylamide in a moderately-frozen aqueous medium yields cross-linked high-swelling cryogels instead of soluble polymers that are formed in water solutions at positive temperatures or both at positive and negative temperatures in formamide media. The comparison of swelling characteristics of the cryogels and especially synthesized cross-linked model hydrogels showed that the amount of crosslinks in the cryogels thus prepared was rather small, no more than 0.05–0.10mol.% with respect to the total quantity of monomer units. The studies performed with NMR and EPR spectroscopies revealed that the crosslinks in such cryogels were formed owing to the generation of certain unexpected by-radicals via coupling of the initiating sulfate-anion-radical with the monomer at the carbonyl group of N,N-dimethylacrylamide. These radicals acted as bifunctional cross-linking agents.