Atom Transfer Radical Polymerization of Poly(ethylene glycol) Dimethacrylate

Reported is an experimental investigation on the atom transfer radical polymerization (ATRP) of poly(ethylene glycol) dimethacrylate (PEGDMA) initiated by an alkyl halide. The polymerization behaviors of PEGDMA in ATRP and in a conventional free radical polymerization were compared with respect to polymerization rate and gel formation. The ATRP of PEGDMA proceeded with a low rate and no observable autoacceleration, while benzoyl peroxide initiated free radical polymerization showed a strong autoacceleration from the beginning of the reaction. The radical signals, as well as copper(II) signals, in the ATRP system were observed by electron spin resonance, confirming the participation of radical intermediates in the ATRP process. At the early stage of polymerization (<40% conversion), the ATRP process proceeded in a living manner with a low and constant radical concentration. However, as the reaction continued, the increased diffusion resistance restricted the mobility of the catalyst/ligand complexes and interrupted the equilibrium between growing radicals and dormant species, resulting in a transition of the reaction mechanism to a conventional free radical polymerization process.