Atom Transfer RaAtom Transfer Radical Polymerization of Methyl Methacrylate Using Bis(2-dodecylsulfanyl-ethyl)-Amine/Copper Bromide: Kinetic Study

Hypothesis: In controlled polymerization methods, atom transfer radical polymerization (ATRP) is one of the most successful methods for the polymerization of various monomers with the controlled pattern. Effect of some important parameters on kinetics of methyl methacrylate polymerization was investigated using 1H NMR and GPC techniques.
In this work, tridentate ligand bis(2-dodecylsulfanyl-ethyl)-amine (SNS) and the Cu(I)Br catalyst of this ligand were synthesized. The ligand and corresponding catalyst were characterized using 1H NMR, UV-Vis and FTIR techniques. ATRP of methyl methacrylate was investigated in bulk state using the SNS/Cu(I)Br and ethyl-2-bromo-2-methyl propionate as initiator in different conditions. The polymerization kinetic was studied by 1H NMR and gravimetric techniques. The kinetic curves of Ln([M]0/[M]t) versus time were plotted and the kpapp was obtained from the curves. The effect of temperature on the kinetics was studied by on-line 1H NMR spectroscopy (75 and 90°C). The effect of the monomer to initiator ratio (500:1, 600:1, 700:1) was investigated at 90°C. In order to confirm the effect of other variables (temperature, catalyst and monomer concentration) on polymerization kinetics, we employed gravimetric method.
Finding: The linear correlation of Ln([M]0/[M]t) versus time and narrow molecular weight distribution (~1.2) revealed that the polymerization reaction process was according to the controlled/“living” radical polymerization. With increasing the temperature, the polymerization rate also increased, and the temperature of 90°C was used as the optimum in subsequent studies. The kinetic plots revealed that in bulk state due to the role of monomer as solvent, the polymerization rate decreased with increasing the monomer content, and subsequently reducing the concentration of the initiator. The effect of the ligand to Cu(I)Br ratio (1:1, 1.5:1, 2:1) on the polymerization kinetic was studied and the results showed increased polymerization rate due to the greater solubility of the catalyst at high ligand concentration.