Synthesis, characterization, and modeling of double-hydrophobic model networks based on cross-linked star copolymers of n-butyl methacrylate and methyl methacrylate
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Seven model networks of a new structure, that of cross-linked "in-out"\star polymers, were synthesized by the group transfer polymerization of the Hydrophobic monomers methyl methacrylate (MMA) and n-butyl methacrylate (BuMA) and the cross-linker ethylene glycol dimethacrylate in a one-pot preparation. From the seven networks, two were the homopolymer networks of MMA and BuMA, while the remaining five were based on equimolar MMA-BuMA copolymer stars of different architectures: heteroarm (two), star block (two), and statistical. The synthesis of the networks involved at least four steps, starting from the synthesis of the linear polymers, proceeding to the preparation of the "arm-first" and "in-out" star polymers, and being completed with the cross-linking of the stars into a network. All the precursors to the networks were characterized in terms of their molecular weights using gel permeation chromatography. The sol fraction extracted from the networks was found to be equal to or lower than 20%. The degrees of swelling (DSs) in n-hexane/tetrahydrofuran (THF) mixtures of all networks increased with the solvent content in THF, a nonselective solvent, and this trend was confirmed by thermodynamic calculations. The DS in a 50-50 n-hexane-THF mixture of the statistical network was found to be the same as those of the segmented networks, suggesting absence of microphase separation in the latter type of networks, a trend confirmed by thermodynamic predictions. © 2006 American Chemical Society.