Polyacrylamide crosslinked by bis-vinylimidazolium bromide for high elastic and stable hydrogels

Abstract

A series of ionic compounds 1,n-dialkyl-3,3'-bis-l-vinylimidazolium bromide (C _n VIM) are prepared and employed to crosslink acrylamide for polyacrylamide (PAAM) hydrogel preparation via in situ solution polymerization. The swelling behavior, mechanical properties and thermal stability of the prepared C _n VIM crosslinked PAAM hydrogels are investigated. C _n VIM effectively crosslink the PAAM networks to form porous structures in the hydrogel, which could stably absorb water as much as 75.9 fold in weight without structural degradation. The prepared hydrogels could endure compressive stress up to 1.95 MPa and compressive deformation more than 90%. Meanwhile, the C _n VIM crosslinked networks show superior thermal stability, and could retain the structural integrity under 150 °C for more than 240 h. The swelling degradation resistance, mechanical strength and thermal stability of C _n VIM crosslinked hydrogels are much better than those of a conventional N,N'-methylenebisacrylamide crosslinked PAAM hydrogel. Using bis-vinylimidazolium bromides as crosslinkers provides an optional strategy for constructing thermally and mechanically robust hydrogel networks.

Fig. 1. Schematic diagram of C_nVIM–PAAM hydrogel preparation and image of the resultant hydrogel.

Fig. 2. (a) ¹H NMR spectrum of C₆VIM in D₂O; (b) IR spectra of C₆VIM, AAM and dried C₆VIM–PAAM.

Fig. 3. SEM images of (a) freeze-dried C₂VIM–PAAM, (b) C₆VIM–PAAM, (c) C₁₀VIM–PAAM.

Fig. 4. (a) SR and EWC of the hydrogels as a function of time; (b) images of C₆VIM–PAAM hydrogel under as-prepared state and equilibrium state.

Fig. 5. The storage modulus (solid symbols) and loss modulus (open symbols) of the hydrogels at 25 °C obtained from DMA tests.

Fig. 6. (a) Compressive stress–strain curves of the hydrogels (inset is the compressive modulus, the fracture stress and the fracture strain of the hydrogels obtained from the curves); (b) and (c) images of the C₆VIM–PAAM hydrogel under compression and slicing with a blade, respectively; (d) and (e) images of the MBA–PAAM hydrogel under compression and slicing with a blade, respectively.

Fig. 7. TGA curves of the freeze-dried C₆VIM–PAAM and MBA–PAAM hydrogels (inset is the DTG curves of the hydrogels).

Fig. 8. (a) Plateau storage modulus of C_nVIM–PAAM hydrogels aged at 150 °C as a function of time; (b) images of C₆VIM–PAAM hydrogel aged at 150 °C for 240 h; (c) image of C₂VIM–PAAM hydrogel aged at 150 °C for 80 h; (d) images of MBA–PAAM hydrogels aged at 150 °C for 8 h.