The synthesis of well‐defined, nearly monodispersed, 3‐miktoarm (from the greek word μlkτós meaning mixed) star copolymer of the A2B type is described. A and B is either polystyrene (PS), polybutadiene (PBd), or polyisoprene (PI). The sequential controlled addition of living anionic B and A chains to methyltrichlorosilane leads to narrow molecular weight distribution miktoarm star copolymers with homogeneous composition. Characterization was carried out by size exclusion chromatography, low‐angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, nuclear magnetic resonance and ultraviolet spectroscopy. Analysis of [η], RH and Rv of the A2B and one A2B2 miktoarm copolymers, suggests that a small expansion of the copolymer occurs either in a good solvent for both species or in a Θ solvent for one of them, as compared with the corresponding star homopolymers. This is in contrast to results obtained on linear block copolymers, and is due to the increased occurrence of heterocontacts in the miktoarm starshaped architecture. © 1995 John Wiley & Sons, Inc.

Block copolymers of styrene and stearyl methacrylate were prepared using anionic polymerization high-vacuum techniques by sequential addition of monomers. Narrow molecular weight distribution copolymers of different molecular weight and composition were obtained. The molecular characteristics of the copolymers were obtained by size exclusion chromatography, membrane osmometry, low-angle laser light scattering (LALLS), and differential scanning calorimetry. Comparative studies in the selective solvents for the polystyrene block, ethyl and methyl acetate, showed that mainly unimolecular micelles are formed in the former, whereas larger aggregates are observed in the latter solvent. LALLS, viscometry, and dynamic light scattering were used to characterize the micelles.

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Intrinsic viscosity, [η], weight‐average molecular weight, Mw, relationships are reported for narrow molecular weight distribution linear polyisoprene and polystyrene samples in CCl4 at 25°C. Molecular weight values cover a range nearly two orders in magnitude, extending as low as 3 × 103. In the case of polystyrene there exists a molecular weight range (around Mw = 16,700) corresponding to a change in the Mark‐Houwink‐Sakurada (MHS) exponent from α = 0.71 to α = 0.54. Comparisons between the viscometric and hydrodynamic radii, from literature data, are made. For polyisoprene the MHS relationship is reported in CCl4, for the first time. For this case α = 0.713 for the whole range of molecular weights studied. Values for the second virial coefficient from low‐angle light‐scattering measurements support the conclusions drawn from viscometry that CCl4 is a good solvent for both polymers studied. The different behavior of the MHS exponent may be attributed to the difference in chain flexibility. © 1995 John Wiley & Sons, Inc.

The micellization properties of well‐defined block copolymers of styrene and decyl methacrylate (SDMA) were studied in two different solvents, methyl acetate (MAc) selective for the polystyrene (PS) block and dodecane, selective for the poly(decyl methacrylate) (PDMA) block. The results were compared with those obtained, in the same solvents, from block copolymers of styrene and stearyl methacrylate (SSMA). In MAc, SDMA copolymers with a decyl methacrylate (DMA) content of 15% or less formed unimolecular micelles, whereas those with a content of 18.5% or higher formed multimolecular micelles. The degrees of association were lower than the corresponding SSMA samples. In dodecane, SDMA form large, monodisperse, spherical, and thermally stable micelles with degrees of association higher than the corresponding SSMA samples. The different behaviors can be attributed to the steric hindrance effect and the ability of the long alkyl groups of the polymethacrylate, MA blocks to crystallize. When the MA blocks are in the soluble corona of the micelles, the steric hindrance effect prevails, thus leading to higher degrees of association for the less bulky alkyl group. In the case where the MA block is in the insoluble core of the micelles, the higher the tendency for crystallization the higher the degree of association. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4177–4188, 2004