Preparation and kinetic characterization of copolymers of acrylamide and poly(ethylene glycol) (meth)acrylate macromonomers

Novel comb copolymers were prepared by the free-radical copolymerization of acrylamide (AM) and poly(ethylene glycol) (PEG) macromonomers in aqueous solution using potassium persulfate as an initiator. The reactivity ratios of acrylamide (M1) toward macromonomers (M2), r1 = Kp11Kp12, were estimated at low conversion by using 1H nuclear magnetic resonance (n.m.r.) spectroscopy and high performance liquid chromatography (h.p.l.c.) techniques. The values of r1 ranged between 1.35 and 2.2 and were dependent on the PEG pendant chain length in the macromonomers. The reactivity of the macromonomers in copolymerization, characterized by (1/r1), decreased with the PEG pendant chain length. The reactivity of the macromonomer in homopolymerization, expressed as KpKt12, increased with the PEG pendant chain length. The changes of Kp and Kt are probably caused by the shielding effect on the growing radicals by the macromonomer pendant chains. The molecular weights of the copolymers were found to be sensitive to the polymerization temperature. Higher-molecular-weight (> 3 × 106) copolymers were obtained at lower temperatures.