Interpolymer Hydrogen-Bonding Complexation Induced Micellization from Polystyrene-b-poly(methyl methacrylate) and PS(OH) in Toluene Shiyong Liu, † Hui Zhu, † Hanyin Zhao, † Ming Jiang,* ,† and Chi Wu ‡,§ Institute of Macromolecular Science and Laboratory of Molecular Engineering of Polymers, Fudan University, Shanghai 200433, China, Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong, and The Open Laboratory of Bond-Selective Chemistry, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui, China Received October 1, 1999. In Final Form: January 3, 2000 In this paper, we suggest a new approach to macromolecular assembly by hydrogen-bonding complexation leading to a micelle-like structure from block copolymers in nonselective solvents. The hydrogen bonding between polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) and poly{styrene-co-[p-(2,2,2-trifluoro- 1-hydroxy-1-trifluoromethyl)ethyl-R-methylstyrene]} (PS(OH)) in toluene led to a stable core-shell structure with the core and shell, respectively, made of the insoluble PMMA/PS(OH) complexes and the soluble PS blocks as long as the p-(2,2,2-trifluoro-1-hydroxy-1-trifluoromethyl)ethyl-R-methylstyrene (HFMS) content of PS(OH) is higher than 8 mol %. Laser light scattering studies found that the molar mass and the core density of the complex micelles increased, but the size decreased as the HFMS content increased. The complexation-induced micelles were very stable, as dilution had almost no effect on them. However, both the size and molar mass of the complex micelles increased as the initial polymer concentration increased, indicating that the complexation was a diffusion-controlled process and the micellization process may not reach thermodynamic equilibrium. In addition, fluorescence and viscometry measurements further supported the concept of formation of hydrogen bonding complex micelles and their dependence on HFMS content in PS(OH). Introduction It is well-known that block or graft copolymers can self- assemble in selective solvents to form micelles with a core- shell structure. 1-4 The driving force for micellization is generally attributed to the microphase precipitation of the insoluble blocks and the affinity of the soluble blocks to the solvent. Such micelles, due to their small size (several tens of nanometers) and high stability (low critical micellization concentration), 3-5 may have promising ap- plications in fields such as drug delivery, 6,7 diagnosis, 8 and separation technology. 9 Therefore, micellization of block copolymers in their selective solvents has been extensively studied in the last two decades. Another effective way of forming block-copolymer mi- celles, which has been reported only in recent years, is associated with interpolymer complexation. The general idea of the approach is as follows. In a solution blend made of a diblock copolymer A-b-B and polymer C, where the solvent is good for A, B, and C, if specific interactions between C and one of the blocks in A-b-B leads to an insoluble complex, the complexation can induce the formation of a core-shell micelle-like structure with the complexes as the core and the remaining soluble block as the shell. It is also very well-known that both ionic interactions and hydrogen bonding between complemen- tary polymers result in interpolymer complexes. Recently, Kataoka et al. and Kabanov et al. have successfully investigated a series of a new type of polymer micelles based on interpolymer ionic interactions. Here the block copolymers contain a charged block which forms a complex with an oppositely charged homopolyeletrolyte in water. The reported polymer pairs include poly(ethylene oxide)- b-poly(L-lysine)/poly(ethylene oxide)-b-poly(R,-aspartic acid), 10,11 poly(ethylene oxide)-b-sodium polymethacrylate/ poly(N-ethyl-4-vinyl pyridinium), 12 poly(ethylene glycol)- b-poly(L-lysine)/oligo-nucleotide, 13 poly(ethylene glycol)- b-poly(aspartic acid)/lysozyme, 14 and poly(ethylene oxide)- b-polymethacrylate anions/N-alkypyridinium cations. 15 This has obviously widened the research area of block- copolymer micellization and shows encouraging prospects in transporting biopolymers 10,13,14 and realizing molecular recognition. 11 In this paper we report, as a first example, micellization of block copolymers and a random copolymer in a nonselective solvent caused by interpolymer hydrogen- * To whom correspondence should be addressed. † Fudan University. ‡ Chinese University of Hong Kong. § University of Science and Technology of China. (1) Halperin, A.; Tirrell, M.; Lodge, T. P. Adv. Polym. Sci. 1992, 100, 31. 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