Accelerated controlled radical polymerization of methacrylates

BACKGROUND: Nitroxide adducts 1,1-ditertbutyl-1-(1-methyl-1-cyanoethoxy)-amine (AIBN/DBN), 1,1-ditertbutyl-1-(benzoylperoxy)-amine (BPO/DBN) and 2,2,6,6,-tetramethyl-4-oxo-1-(1-methyl-1-cyanoethoxy)-piperidine (AIBN/4-OXO-TEMPO) were prepared and evaluated as stabilized unimolecular initiators for controlled radical polymerization of methacrylate monomers using sulfuric acid as an accelerating additive. Their effectiveness was evaluated from polymerization rates, molecular weight control and dispersity (D) of the polymers. Thermal stabilities of the polymers were also examined. The monomers used were methyl methacrylate, triethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA). RESULTS: Polymerization was accomplished at 70 and 130 degrees C in 5 min to 144 h. The value of D of poly(methyl methacrylate) (PMMA) was 1.05-1.22. The glass transition temperature (T-g) for PMMA was 122-127 degrees C. The activity of the chain ends was established by chain extension and controlled polymerization was established by plotting M-n versus monomer conversion. First-order kinetics in monomer consumption was established and an electron paramagnetic resonance study was conducted. Decomposition temperature (T-d) for PMMA was 360-380 degrees C, for poly(TEGDMA) was 300-380 degrees C and for poly(EBPADMA) was 360-440 degrees C. Photoinitiation without additive yielded no polymer. Thermal initiation by AIBN/4-OXO-TEMPO was the fastest. CONCLUSIONS: The initiators are applicable in low-temperature additive-enhanced controlled polymerization of methacylates and dimethacrylates, producing polymers with excellent attributes and a low value of D. (C) 2008 Society of Chemical Industry