Halide exchange during atom transfer radical polymerization (ATRP) using mixed halide initiation systems, R-X/Cu-Y (X, Y ) Cl or Br), was investigated. Model studies of mixed halide initiation systems (i.e., R-X/Cu-Y, X * Y) demonstrated that exchange occurs rapidly at 90 °C, and there is a clear preference for alkyl chlorides to be formed in over alkyl bromides. This was attributed mainly to the carbon-chlorine bond being stronger than the corresponding carbon-bromine bond. This implies that, in ATRP with a mixed halide initiator/catalyst system, the bulk of the polymer chain ends are terminated by chlorine if [CuCl] 0 g [RBr]0. Examples of using this information to improve the control in ATRP of methyl methacrylate (MMA) are presented. It was shown that, when benzyl halides were used as the initiator in the ATRP of MMA, the rate of initiation was increased relative to the rate of propagation, thus providing better control by using the benzyl bromide/copper chloride mixed halide system. Better molecular weight control at high conversions of monomer to polymer was observed when using ethyl 2-bromoisobutyrate and copper chloride as initiator/catalyst in comparison to using ethyl 2-bromoisobutyrate/copper bromide, indicating that side reactions are less significant in the former.

The synthesis of di- and triblock copolymers, involving methyl methacrylate (MMA), butyl acrylate, and methyl acrylate, using copper-based atom transfer radical polymerization (ATRP) is reported. It was found that poly(MMA) macroinitiator is able to initiate the ATRP of acrylic monomers. However, for polyacrylates to effectively initiate the ATRP of MMA, the end group should be a bromine atom and the catalyst CuCl; that is, halogen exchange should take place. ABA-type triblock copolymers, where B = poly(butyl acrylate) and A = poly(methyl methacrylate), were synthesized by growing the center block first using a difunctional initiator and then adding MMA to the ends.

The homogeneous controlled/“living” free radical polymerization of methyl methacrylate (MMA) by atom transfer radical polymerization (ATRP) using a CuIX/4,4‘-di(5-nonyl)-2,2‘-bipyridine catalytic system (X = Cl, Br) with various initiators R−X was investigated. The rates of polymerization initiated by most of the systems exhibited first-order kinetics with respect to the monomer. A linear increase of number average molecular weight (M n) versus monomer conversion was observed for most of these initiation systems. The benzhydryl chloride/CuICl system yielded the lowest rate of polymerization, which could be increased by slow addition of the initiator. The reduced rate of polymerization was due to an increase in the concentration of CuIICl, which results from the coupling of benzhydryl radicals during initiation. The slow addition of benzhydryl chloride prevented the formation of a large amount of benzhydryl radicals in the initiation step, thereby reducing radical−radical termination and CuII formation, and led to an increase in the rate of polymerization. p-Toluenesulfonyl chloride/CuIBr gave better control of molecular weight and lower polydispersities than p-TsCl/CuICl, possibly due to the faster deactivation step in ATRP. Ethyl 2-bromoisobutyrate/CuIBr gave the fastest rate of polymerization among all the initiation systems but showed some deviation in M n at high conversions. The initiation efficiencies of diethyl 2-bromomalonate and diethyl 2-bromo-2-methylmalonate in the ATRP of MMA were examined. The latter can initiate polymerization efficiently, while the former gave no polymerization. This can be explained by the difference in the electronic nature of the two malonyl radicals generated during initiation. Such experimental observations, coupled with data from the literature, lead to some general “rules” by which successful initiation of ATRP can be achieved.

The homogeneous controlled/“living” radical polymerization of methyl methacrylate (MMA) using the atom transfer radical polymerization (ATRP) with CuCl/4,4‘-di(5-nonyl)-2,2‘-bipyridine catalytic system and diphenyl ether as the solvent generated well-defined polymers with polydispersities M w/M n ≤ 1.2. The evolution of the molecular weights of the polymers follows the ratio of the mass of the consumed monomer to the initial initiator concentration. The rate of polymerization follows first-order kinetics with respect to the decrease of monomer concentration. The polymerization rate reaches a maximum when the ratio of ligand-to-CuICl is one-to-one. ATRP of MMA shows first-order kinetics with respect to both CuICl and the initiator, alkyl or sulfonyl chloride. The rate of polymerization did not obey simple negative first-order kinetics with respect to the concentration of CuIICl, partially due to a persistent radical effect, which resulted in the increase of [CuIICl] in the initial stage of polymerization. Thermodynamic data and activation parameters for the solution ATRP of MMA are reported.

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