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

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 ( G '). Generally with increasing cross-linker content, G ' values of the hydrogels increased, while S values decreased. The different polymerizable cross-linker end groups resulted in a decrease of G ' in the following order for cross-linkers with C 4 spacers: acrylamide > maleimide > methacrylamide > vinylsulfonamide. Longer cross-linker alkyl spacer lengths caused an increase in G ' and a decrease in S . Independent of the cross-linker used, a universal correlation between G ' and equilibrium polymer volume fraction ϕ was found. For PAAm hydrogels, G ' ranged between 4 kPa and 23 kPa and ϕ between 0.07 and 0.14. For PDMAAm hydrogels, G ' ranged between 0.1 kPa and 4.9 kPa and ϕ between 0.02 and 0.06. The collected data were used to establish an empirical model to predict G ' depending on ϕ . G ' of PAAm and PDMAAm hydrogels is given by G ' = 4034 kPa ϕ 2.66 and G ' = 4297 kPa ϕ 2.46 , respectively.