Tuning the Synthetic Routes of Dimethylaminoethyl methacrylate‐Based Superabsorbent Copolymer Hydrogels Containing Sulfonate Groups: Elasticity, Dynamic, and Equilibrium Swelling Properties

Abstract

Superabsorbent copolymer hydrogels based on N,N‐dimethylaminoethyl methacrylate (DMAEMA) and 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) were synthesized by free‐radical cross‐linking copolymerization using a bifunctional cross‐linking agent diethylene glycol dimethacrylate (DEGDMA). Poly(DMAEMA‐co‐AMPS) (P(DMAEMA‐co‐AMPS)) hydrogels were prepared at a fixed cross‐linker ratio, but at various ionic comonomer AMPS content between 0 and 50 mol%. The effect of ionic comonomer concentration on the equilibrium swelling, mechanical behavior, and swelling–deswelling kinetics was investigated to find materials with satisfactory swelling and elastic properties. The increase in the ionic comonomer AMPS content increased the equilibrium swelling of copolymer hydrogels. Using the Flory–Rehner theory, the equilibrium swelling behavior of P(DMAEMA‐co‐AMPS) hydrogels was successfully investigated and the effective charge density of the resulting copolymer hydrogels was calculated as an adjustable parameter. Scaling rules were derived for the ionic group content to explain the observed swelling behavior of P(DMAEMA‐co‐AMPS) hydrogels. The kinetics of copolymer hydrogel swelling as well as the mechanism of diffusion was investigated by dynamic swelling measurements at different pH values. The dominant physical mechanism controlling the water uptake of P(DMAEMA‐co‐AMPS) copolymer hydrogels was analyzed, and the diffusion coefficients were determined. The transport was found to be less Fickian for the copolymer hydrogels containing AMPS below 30 mol% at acidic pH values where the polymer networks were ionized.

Scaling Behavior and Structure–Property Relationships of Multifunctional Ternary‐Hydrogels Based on N‐Alkyl Methacrylate Esters: Property Tunability through Versatile Synthesis

“…Data for P(DMAEMA-HPMA), P(DMAEMA-AMPS), P(HPMA-GMA), and P(DEAEMA-HEMA-AMPS) hydrogels were taken from the literature. [35][36][37][38] pressure. Balancing the two opposite contributions by minimizing their sum with respect to 𝜈 2 provides the following prediction…”

“…Data for P(DMAEMA-HPMA), P(DMAEMA-AMPS), P(HPMA-GMA), and P(DEAEMA-HEMA-AMPS) hydrogels were taken from the literature. [36][37][38][39] tetraethyleneglycol dimethacrylate (TEGDMA) as crosslinker with X = 1/76 and DMAEMA mol% has been varied between 0 and 100 mol%. The total molar concentration of monomers (HPMA, DMAEMA, and TEGDMA) was kept at 1.60 m. [35] Here, it is necessary to take into account that, in the present terpolymer PHDm/Gn-Hgs, the amount of HPMA is kept constant at 20 mol% and the amount of DMAEMA is varied between 80 and 0 mol%.…”

“…P(DMAEMA-AMPS) hydrogels were prepared using crosslinker DEGDMA with X = 1/50 by keeping the total monomer concentration constant at 1.0 m, and the mole fraction of AMPS in the monomer mixture was varied between 0 and 50 mol%. [37] However, a lower scaling parameter, −0.13, has been reported for ionic P(DEAEMA-HEMA-AMPS) terpolymer gels prepared with diethylaminoethyl methacrylate, DEAEMA, a cationic monomer from N-alkyl methacrylates. [38] AMPS was fixed at 4 mol% and HEMA was varied over a range of mole content from 36 to 96 mol%.…”

“…[35] It is seen that the reduced moduli of these two systems, which contain components similar to terpolymer PHDm/Gn-Hgs, decrease with increasing degree of swelling. However, for P(DMAEMA-AMPS) [37] and P(DEAEMA-HEMA-AMPS) hydrogels, [38] G r values increase with rising swelling ratio, and the exponents become 0.12 and 0.21, respectively. The increase of reduced modulus with increasing swelling is due to the finite extensibility of the network chains.…”

“…The dotted curves are the best fit to the experimental results. Data for P(DMAEMA-HPMA), P(DMAEMA-AMPS), P(HPMA-GMA), and P(DEAEMA-HEMA-AMPS) hydrogels were taken from the literature [35][36][37][38].…”