In this study based on the formation mechanism of impurities in synthesis process of DADMAC monomer, we reported the development and validation of a new method using gas chromatography (GC) coupled with solvent extraction to detect impurities in DADMAC monomer solution.
According to , standard solution of DADMAC monomer (60 wt%) was prepared by dissolving DADMAC crystal into double distilled water.
The tested DADMAC monomer solution (10 mL, 60 wt%) with impurities was placed in a 25 mL separatory funnel, and then a volume of 10 mL extraction solvent trichloromethane was added into the solution by a pipette.
In order to investigate the extraction efficiency, standard solution of DADMAC monomer was prepared by adding appropriate amounts of analysis standards and then processed as aforementioned solvent extraction procedure.
Next, DMAM and DADMAC were mixed into the solution with 210 rpm constant stirring speed.
The corresponding optimal synthesis conditions can be concluded from the curves: the reaction temperature is 60[degrees]C; the pH value is 6; the monomer concentration of AMPS/DADMAC/DMAM/AA is 18 wt%; the initiator concentration is 0.7% by weight of total monomers; the weight ratio of AMPS, DADMAC, DMAM, and AA is 6.3:1.8:1.5:0.4; and the reaction time is 140 min.
The absorption peak around 3014.4 [cm.sup.-1] can be attributed to the stretching vibration of methylene group in the carbon-nitrogen quinary heterocyclic structures of DADMAC and its deformation vibration is around 960.4 [cm.sup.-1] .
The peaks at 2.484-2.643 ppm are corresponded to the protons of [H.sub.c] and [H.sub.f] in DADMAC and DMAM respectively, and the methyl protons (--C[H.sub.3]) located at the chemical shift of [delta] = 2.866 and 2.941 .
There are more significant differences in the reactivity ratios of AM and DADMAC
(([r.sub.1](AM) = 6.4, [r.sub.2](DADMAC
) = 0.06).
DADMAC was received from Fluka, and it is in salt form and fully ionized at all pH values within our working range.
Free radical polymerization of DADMAC may proceed as a cyclopolymerization mechanism.
RI detector, calibrated with aqueous NaCl, signals were used to monitor monomer concentration and its conversion to polymer by using the differential RI increment differences (<dn/dc) between the values of DADMAC and PDADMAC.