Stereocontrol in Radical Polymerization of Acrylamides with Combined Lewis Acids of AlCl3-FeCl2

The radical polymerizations of acrylamide (AM) and N,N -dimethyl acrylamide (DMAA) were carried out in the presence of combined Lewis acids of AlCl3-FeCl2 system. Comparing with the polymerization produced in a single Lewis acid system of AlCl3 or FeCl2, the AM polymerization catalyzed by a combined AlCl3-FeCl2 composite in CHCl3 produced a polymer with higher isotacticity (m = 36%). The DMAA polymerization in the presence of AlCl3-FeCl2 composite produced a polymer of higher isotacticity (m = 83%) in CHCl3 and a much higher isotacticity (m = 91%) in toluene. The molecular weight and polydispersity of PAM and PDMAA show identical results whether polymerized in the presence or absence of Lewis acids. The combined Lewis acids showed great isotacticity in a lower polar solvent and the stereochemistry of the polymerization was clearly affected by the molar ratio of combined Lewis acids (AlCl3 - FeCl2). The polymerization of AM in the presence of 0.03-0.03 mol/L AlCl3-FeCl2 composite system gave a polymer with dyad tacticity of 59/41 (m/r), the polymerization of DMAA in the presence of 0.015-0.015 mol/L AlCl3-FeCl2 composite system gave a polymer with dyad tacticity of 95/5 (m/r). Furthermore, the isotactic specificity of combined Lewis acids on AM and DMAA were also influenced by aging temperature and aging time. The optimum aging temperature of polymerization was 80°C, and the optimum aging time was 1 h.