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.
A silica gel support system for the copper bromide−hexamethyltriethylenetetramine
(HMTETA) complex was successfully developed for the atom transfer radical polymerization (ATRP) of
methyl methacrylate (MMA) in toluene. The supported complex mediated a living polymerization of MMA,
yielding polymers with controlled molecular weights and narrow molecular weight distributions. The
MMA concentration had significant influence on the polymerization behavior. At 33% MMA concentration,
the polymerization catalyzed by CuBr−HMTETA/silica gel followed typical first-order kinetics with respect
to the monomer. But at 50% MMA, the polymerization significantly deviated from the first-order kinetics
after the MMA conversion reached 30%. The supported catalysts were recycled for second and third uses.
The recycled catalysts remained 80% active in the second use and 50% in the third use relative to their
initial activity. The recycled catalysts had even better controllability over the polymerization. The
molecular weights of PMMA produced agreed with the predicted values, and the polydispersities were
less than 1.2.
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