Atom transfer radical polymerization of poly(ethylene glycol) dimethacrylate

Reported is an experimental investigation on the atom transfer radical poly merization (ATRP) of poly(ethylene glycol) dimethacrylate (PEGDMA) initiate d by an alkyl halide. The polymerization behaviors of PEGDMA in ATRP and in a conventional free radical polymerization were compared with respect to p olymerization rate and gel formation. The ATRP of PEGDMA proceeded with a l ow rate and no observable autoacceleration, while benzoyl peroxide initiate d free radical polymerization showed a strong autoacceleration from the beg inning of the reaction. The radical signals, as well as copper(II) signals, in the ATRP system were observed by electron spin resonance, confirming th e 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 th e reaction continued, the increased diffusion resistance restricted the mob ility of the catalyst/ligand complexes and interrupted the equilibrium betw een growing radicals and dormant species, resulting in a transition of the reaction mechanism to a conventional free radical polymerization process.