LOW-TEMPERATURE LIVING RADICAL POLYMERIZATION (ATOM-TRANSFER POLYMERIZATION) OF METHYL-METHACRYLATE MEDIATED BY COPPER(I) N-ALKYL-2-PYRIDYLMETHANIMINE COMPLEXES

This paper demonstrates that atom transfer polymerization of methyl me thacrylate mediated by CuBr/N-alkyl-2-pyridylmethanimine complexes in toluene proceeds effectively at temperatures as low as 15 degrees C, w hile maintaining control over molecular weights and yielding narrow po lydispersity indexes. The reaction can even be performed at - 15 degre es C with a number average molecular weight, M-n, of 6980 and a polydi spersity, PDI, of 1.28 being achieved in 116 h; however, the molecular weight control is less effective. The polymerizations were performed at 90, 60, 40, and 15 degrees C with the first-order rate plots, molec ular weight vs conversion plots, and final polydispersity indexes cons istent with little or no termination-living/controlled polymerization. Methyl hydroquinone (MeHQ) has been demonstrated to accelerate the po lymerization by a factor of 3-4 at temperatures below 40 degrees C; An activation energy, E-a, for polymerization in the absence of phenol w as determined to be 60.3 kJ . mol(-1) and is significantly reduced to 44.9 kJ . mol(-1) in the presence of MeHQ. These results suggest that coordinating phenols modify the active polymerization center. The ster eochemistry of the polymers produced are consistent with that observed for conventional free-radical polymerization in that the fraction of syndiotactic arrangements increases as the reaction temperature is low ered. At 90 degrees C, 59.1% rr triads are obtained with a persistence ratio of 0.924 and at -15 degrees C, 71.5% rr triads are obtained.