Articles Allyl Halide (Macro)initiators in ATRP: Synthesis of Block Copolymers with Polyisobutylene Segments Wojciech Jakubowski, † Nicolay V. Tsarevsky, † Tomoya Higashihara, ‡ Rudolf Faust, ‡ and Krzysztof Matyjaszewski* ,† Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon UniVersity, 4400 Fifth AVenue, Pittsburgh, PennsylVania 15213, and Department of Chemistry, UniVersity of Massachusetts Lowell, One UniVersity AVenue, Lowell, Massachusetts 01854 ReceiVed December 13, 2007; ReVised Manuscript ReceiVed February 4, 2008 ABSTRACT: Allyl halides (allyl-X) and polyisobutylene with allyl halide end group (PIB-allyl-X where X ) Cl, Br) were investigated as (macro)initiators in atom transfer radical polymerization (ATRP). Studies with low molecular weight allyl halide initiators that model the PIB-allyl-X macroinitiator were performed first. Poly- merization of styrene (St) using allyl halides in the presence of CuX/4,4′-di(5-nonyl)-2,2′-bipyridine (dNbpy) catalyst was controlled, but polystyrene with lower polydispersity was obtained with the Br-based initiator-catalyst system. ATRP of methyl methacrylate (MMA) initiated by allyl halides was not as successful. Polymerization of MMA with allyl-Cl and CuCl/dNbpy catalyst resulted in polymer with molecular weight 4 times higher than the predicted value. The polymerization initiated by allyl-Br in the presence of CuCl/dNbpy catalyst was better controlled but still resulted in polymers with molecular weights 2 times higher than the theoretical values. The addition of 10 mol % St to MMA significantly improved the polymerization control. The values of the ATRP equilibrium constants (K ATRP ) of allyl halides were determined and were close to these of 2-haloisobutyrates. Therefore, the low initiation efficiency from allyl-Br during ATRP of MMA is predominantly caused by the slow addition of allyl radical to monomer rather than low K ATRP . Extension from PIB-allyl-Br was then conducted to obtain well-defined block copolymers. For example, starting from PIB-allyl-Br macroinitiator (M n ) 4600 g/mol, M w /M n ) 1.12), a polyisobutylene-b-polystyrene (PIB-b-PSt, M n ) 21 400 g/mol, M w /M n ) 1.14), and polyisobutylene-b-poly(methyl methacrylate-co-styrene) (PIB-b-P(MMA-co-St), M n ) 26 000 g/mol, M w /M n ) 1.32) were obtained. Extension of PIB-allyl-Br with MMA without styrene resulted in a block copolymer with a bimodal molecular weight distribution. Introduction As new polymeric materials are in demand, block copolymers are becoming more and more important. Block copolymers, defined as macromolecules composed of two or more continuous sequences of chemically different repeat units, continue to remain a subject of intense research and technological interest due to their unusual and useful properties. 1,2 Current and potential high-technology applications of block copolymers are based on their ability to self-assemble, in bulk as well as in selective solvents, into ordered nanostructures. 3,4 Domain size and shape as well as the interdomain distance in these nano- structures can be manipulated by changing the molecular weight, chemical structures, molecular architecture, and composition of block copolymers. Therefore, synthetic procedures that allow for the efficient synthesis of well-defined segmented copolymers are becoming increasingly important. High-performance applications require well-defined and properly designed block copolymers. The access to well-defined block copolymers was opened by Szwarc in the early 1950s by developing the living anionic polymerization. 5 Subsequently, other mechanisms were employed to prepare well-defined block copolymers. 6 An interesting possibility is to prepare block copolymers by the combination of two different mechanisms. 7 This way it is possible to expand the range of accessible block copolymers. For example, polyisobutylene (PIB), 8–11 a very important commercial material, can be prepared only via cationic polymerization. PIB-based block copolymers have attracted significant interest because of their unique properties such as UV and thermo-oxidative stability resulting from the saturated backbone structure. Additional important features of these materials include high mechanical damping, high gas barrier properties, biocompatibility, and biostability. Their commercial potential as thermoplastic elastomers and biomaterials has been the subject of a number of research papers and reviews. 12–19 However, cationic polymerization cannot be used for the synthesis of other interesting segments such as poly(meth)acrylates. They can be readily prepared by radical or anionic polymerization. Thus, the synthesis of the polyisobutylene-poly(meth)acrylate block copolymers requires some type of mechanistic transformation. Since alkyl halides are at the chain end of “living” polyisobutylene, the simplest approach may be based on employing them for atom transfer radical polymerization (ATRP). 20–25 However, tertiary alkyl halides are poor ATRP initiators. Difunctional PIB, capped with several units of styrene, Cl-St-b-PIB-b-St-Cl, prepared cationically was used as an efficient difunctional macroinitiator for homogeneous ATRP. It was extended via ATRP with well- defined segments built from styrene (St), methyl acrylate (MA), * Corresponding author. E-mail: km3b@andrew.cmu.edum. † Carnegie Mellon University. ‡ University of Massachusetts Lowell. 2318 Macromolecules 2008, 41, 2318-2323 10.1021/ma7027837 CCC: $40.75  2008 American Chemical Society Published on Web 03/15/2008