Several controlled/living radical polymerization (CRP) techniques (atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), iodide degenerative transfer polymerization (IDTP), and reversible addition-fragmentation transfer polymerization (RAFT)) were studied for the alternating copolymerization of a donor monomer (styrene) and an acceptor monomer (methyl methacrylate or methyl acrylate) complexed with Lewis acid. RAFT polymerization was found to be the most versatile system. The combination of RAFT and Lewis acids complexation techniques allows synthesis of well-defined alternating copolymers poly(styrene-alt-methyl methacrylate) with controlled molecular weight (up to M n ) 70 000 g mol -1 ), low polydispersities (Mw/Mn < 1.3), and controlled comonomer sequences (∼90% of alternating triads). These results were obtained in the presence of diethylaluminum chloride and ethylaluminum sesquichloride. Moreover, the alternating copolymers obtained in such copolymerizations retain chain end functionality and were used as macroinitiators for the synthesis of well-defined diblock copolymers poly(methyl methacrylate-alt-styrene)-b-polystyrene.

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Introduction. Controlled/"living" radical polymerizations allow complex macromolecular architectures to be synthesized. Numerous examples of star, block, graft, comb, and brush copolymers made by atom transfer radical polymerization (ATRP), reversible additionfragmentation transfer polymerization (RAFT), or nitroxide-mediated polymerization (NMP) have been reported. 1,2 However, only a few studies describe the synthesis of copolymers possessing controlled sequences (gradient or alternating copolymers) by controlled/"living" radical polymerization, even though such structures could open a new avenue for the production of novel materials. Several gradient copolymers have been synthesized by ATRP. 3 Only a few alternating copolymers from comonomers that have a spontaneous tendency for alternation have been synthesized by ATRP, 4-6 RAFT, 7 or NMP. 8 However, the synthesis of alternating copolymers by controlled/"living" radical polymerization from monomers without this tendency has not yet been reported.During the 1960s and 1970s, several studies reported the synthesis of alternating copolymers. 9 Acrylic monomers and styrene, which usually copolymerize randomly, may be copolymerized in an alternating fashion in the presence of Lewis acids. 10,11 Although the precise mechanism of this copolymerization is not yet fully understood, it seems that the alternating behavior is due to the formation of a complex between the acrylic monomer and the Lewis acids which is unable to selfpropagate and strongly enhances the cross-propagation. However, no control of molecular weight and polydispersity was possible in these systems.This communication describes the synthesis of controlled/"living" alternating copolymers of methyl methacrylate (M) with styrene (S) in the presence of diethylaluminum chloride by RAFT. 12 (The RAFT technique was chosen, since it provides smaller interference with Lewis acids than ATRP or NMP.) This new system controls the molecular weight, polydispersity, and the comonomer sequences. To show the superior control of this system, the kinetic behavior and the microstructure of the synthesized polymer have been compared to those obtained in a RAFT copolymerization without Et 2 AlCl and in a conventional radical copolymerization in the presence of Et 2 AlCl.Experimental Part. a. Polymerization Conditions in the Presence of Lewis Acid. In a glovebox, dried methyl methacrylate (1.86 g, 18.6 mmol) and diethylaluminum chloride (0.89 g, 7.4 mmol) were added

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Hydrogels with varying cross-linking densities, and average molecular weights between two consecutive cross-links, were prepared from the binary poly(N-vinyl-2-pyrrolidone)/water and ternary poly(N-vinyl-2-pyrrolidone)/water/K 2 S 2 O 8 systems by irradiation with ␥ -rays at ambient temperature. Both hydrogel systems were employed for diffusion and swelling experiments in 0.00278 M ␣-lactose solution at room temperature. Diffusion of ␣-lactose solution into hydrogels was found to be of the Fickian type. The percent swelling, equilibrium swelling, initial rate of swelling, swelling rate of constant, equilibrium water/␣-lactose content, and diffusion constant values were determined for PVP and PVP/K 2 S 2 O 8 hydrogel systems in 0.00278 M ␣-lactose solution.