Thermochemistry of Acrylamide Polymerization: An Illustration of Auto-acceleration and Gel Effect

Abstract

Addition polymerization of alkenes is an exothermic process due to the relief of the bond strain from C-C double bonds (π bonds) in the monomer molecules. Control of exothermic reactions is crucial for preventing runaway reactions/explosions in the industrial setting. This experiment was designed for undergraduate students to demonstrate the exothermic nature of addition (chain-growth) polymerization and to estimate the enthalpy of polymerization using adiabatic calorimetry technique. Acrylamide (AAM) was polymerized using ammonium persulfate (APS) and Tetramethylethylenediamine (TMEDA) as redox initiators at room temperature. The concentration of AAM monomer was varied in the range of 5-25 wt. %, and the heat of polymerization was calculated from the recorded temperature rise (ΔT). The enthalpy of AAM polymerization (∆Hp) was estimated to be ≈ 16.5-19 kcal/ mole, depending on the monomer concentration. Enthalpy of polymerization was increased with increasing the monomer concentration due the auto-acceleration effect, which was clearly observed for solutions with AAM concentrations of ≥ 20 wt. %. The auto-acceleration phenomenon was identified from the fast and non-linear increase in the rate of temperature rise which reached a maximum of (0.5°C/ s) for solutions with AAM of 25 wt. %. For AAM concentrations of ≥ 20 wt. %, the auto-acceleration was accompanied by the polymer gelation (gel effect) due to the formation of the high molecular weight polyacrylamides.

Magnetic Hyperthermia to Promote Acrylamide Radical Polymerizations

“…To provide an interpretation of the experimental results, the heating–cooling transient during the magnetic hyperthermia-induced polymerization was numerically simulated with the heat transfer model described in the Experimental Part. We used as inputs the SLP of the CoFe 2 O 4 NPs, derived from thermometric measurements, and the enthalpy change associated with the polymerization reaction obtained with differential scanning calorimetry. , The heating efficiency of the CoFe 2 O 4 NPs was estimated by fitting the initial slope of the heating curve (Figure F) to calculate the SLP, which is approximately 60 W/g.…”

“…We used as inputs the SLP of the CoFe 2 O 4 NPs, derived from thermometric measurements, and the enthalpy change associated with the polymerization reaction obtained with differential scanning calorimetry. 56,57 The heating efficiency of the CoFe 2 O 4 NPs was estimated by fitting the initial slope of the heating curve (Figure 2F) to calculate the SLP, which is approximately 60 W/g. Figure 3A shows the time evolution of the temperature, calculated at different points within the magnetic gel (see Figure 3B for their positions).…”

Efficacy of gel electrophoresis for proteins and biotechnological products –an overview.

“…Persulfate ion (S2O8 -), that is added as ammonium persulfate (APS) is act as an initiator for the solidification of gel and also as free radicals source, whereas TEMED (N, N, N', N'-tetra methyl ethylenediamine) act as a catalyst for the reaction of polymerization by stabilizing these free radicals. In some cases, as in the isoelectric focusing the persulfate existence can cause an interference with electrophoresis, and for this reason they replaced by riboflavin and TEMED [40] .…”

Shape memory behaviour of polyacrylamide/MWCNT nanocomposite hydrogel under direct and indirect stimulation

“…PAAm hydrogel was synthesized by radical polymerization with extremely exothermic reaction [7,25]. To prepare the hydrogels containing 85 wt% of water, the reaction mixture was contained of MBAAm as a crosslinking agent, AAm monomer (with a ratio of 200:1 to MBAAm), which was dissolved in distilled water at a concentration of 7% (w/v), and redox initiators (APS and TEMED).…”

“…Polyacrylates, which are water-soluble polymers [6], have a wide range of applications such as oil recovery, water purification, biosensors, micro-encapsulation, drug delivery, and so on [7,8]. Also among the polymers used for preparation of composites/nanocomposites hydrogels, polyacrylate-based hydrogels attracted more attention for two reasons: 1) formation of neutral or alkaline solution in water and 2) formation of hydrogen bonds due to the presence of amine groups [9].…”