Triazole-based cross-linkers in radical polymerization processes: tuning mechanical properties of poly(acrylamide) and poly( -dimethylacrylamide) hydrogels

Abstract

Triazole-based cross-linkers with different spacer lengths and different functional end groups (acrylamides, methacrylamides, maleimides and vinylsulfonamides) were synthesized, investigated for cytotoxic and antibacterial activity, and incorporated into poly(acrylamide) (PAAm) and poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels by free-radical polymerization. Hydrogels prepared with different cross-linkers and cross-linker contents between 0.2% and 1.0% were compared by gel yields, equilibrium degrees of swelling (S) and storage moduli (G0). Generally with increasing cross-linker content, G0 values of the hydrogels increased, while S values decreased. The different polymerizable cross-linker end groups resulted in a decrease of G0 in the following order for cross-linkers with C4 spacers: acrylamide > maleimide > methacrylamide > vinylsulfonamide. Longer cross-linker alkyl spacer lengths caused an increase in G0 and a decrease in S. Independent of the cross-linker used, a universal correlation between G0 and equilibrium polymer volume fraction f was found. For PAAm hydrogels, G0 ranged between 4 kPa and 23 kPa and f between 0.07 and 0.14. For PDMAAm hydrogels, G0 ranged between 0.1 kPa and 4.9 kPa and f between 0.02 and 0.06. The collected data were used to establish an empirical model to predict G0 depending on f. G0 of PAAm and PDMAAm hydrogels is given by G0 ¼ 4034 kPa f2.66 and G0 ¼ 4297 kPa f2.46, respectively.