Controlled radical polymerization of (meth)acrylates by ATRP with NiBr2(PPh3)2 as catalyst

NiBr2(PPh3)(2) has been found to be an efficient catalyst for the ATRP of methyl methacrylate (MMA) and n-butyl acrylate (n-BuA) initiated by an alkyl halide in the absence of any activator (e.g., Lewis acid) at 85 degrees C. The molecular weight distribution of the poly(meth)acrylates is narrow (M-w/M-n = 1.1-1.4). However, some side reactions (more likely coupling reactions) are observed at high monomer conversions in the case of n-BuA. An excess of PPh3 has proved to increase the polymerization rate of MMA while preserving the control of the molecular parameters. When the catalyst/initiator molar ratio is too small(e.g., 0.05), the polymerization rate decreases, the polydispersity increases, and the initiation is less efficient. alpha-Acid and alpha-hydroxyl end groups have been successfully attached to the chains by using functional initiators, such as 2-bromo-2-methylpropionic acid and 2,2',2 "-tribromoethanol. Reactivity ratios for the MMA/n-BuA comonomer pair have been measured and found to be close to the values observed for a conventional free-radical polymerization. Diethyl meso-2, 5-dibromoadipate has been used as a difunctional initiator for the n-BuA polymerization, leading to alpha,omega-bromo-poly(n-BuA) of narrow molecular weight distribution. Finally, the thermal stability of PMMA is consistent with the lack of termination reactions, while T-g is as high as 125 degrees C.