Chemistry for sustainable building materials

N,N’-methylene bisacrylamide (BIS) is a very popular crosslinker for radical polymerisation in water. It is highly reactive but tends to undergo alkaline hydrolysis and suffers from low solubility. This study shows that BIS forms only inhomogeneous networks with slowly polymerising systems such as N,N-diallyldimethylammonium chloride (DADMAC). As a result, gels with very low cross-linking densities, i.e. high swelling capacities, disintegrate during the swelling test. Coherent, i.e. highly cross-linked gels are not accessible due to the solubility limit. A promising alternative are multivalent tetraallyl compounds, such as tetraallylammonium bromide, N,N,N‘,N’-tetraallylpiperazinium dibromide and N,N,N‘,N’-tetraallyltrimethylenedipiperidinedibromide. In contrast to BIS, the copolymerisation with DADMAC is statistic. However, gelation with the new tetraallyl crosslinkers is much slower than with BIS and follows the order TAPB < TAMPB < TAAB, but the differences become significantly smaller as the content increases. At low contents, all three enable the production of gels with high swelling capacities of up to 360 g/g.

T. B. Mrohs, O.Weichold
Multivalent Allylammonium-Based Cross-Linkers for the Synthesis of Homogeneous, Highly Swelling Diallyldimethylammonium Chloride Hydrogels
Gels 2022, 8, 100. https://doi.org/10.3390/gels8020100