Block copolymers of styrene and stearyl methacrylate. Synthesis and micellization properties in selective solvents

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

Synthesis and Solution Properties of Polymethacrylates with Alicyclic Side Groups

The influence of alicyclic side groups on the unperturbed chain dimensions of polymethacrylates is reported. Cyclobutyl, cyclopentyl, cyclooctyl, and cyclododecyl side groups resulted in characteristic ratios respectively of 10.0, 11.2, 12.1, and 14.2. These findings indicate that an increase in the size of the alicyclic side group leads to a concomitant enhancement in C∞. The same trend was previously noted for poly(n-alkyl methacrylates). For alicyclic side groups C∞ is larger than for the corresponding poly(n-alkyl methacrylate). These differences are attributed to the diminished flexibility and closer center of mass (to the backbone) for alicyclic substituents. © 1989, American Chemical Society. All rights reserved

Micellization behavior of diblock and triblock copolymers of poly(t-butyl methacrylate) bearing associating short polystyrene end-blocks

Anionic polymerization high vacuum techniques were employed for the synthesis of a diblock (PS-b-PtBuMA) and two triblock (PS-b-PtBuMA-b-PS) copolymers of polystyrene (PS) and poly(t-butyl methacrylate) (PtBuMA) bearing similar low molecular weight PS end-block(s). Dilute solution viscometry, as well as static and dynamic light scattering, were employed to assess whether the short PS end-blocks were able to promote association in t-amyl alcohol, a selective solvent for PtBuMA. The effect of macromolecular architecture on the association behavior of the copolymers was also examined. © 2008 Elsevier Ltd. All rights reserved

Association behavior of linear co-functionalized polybutadienes in cyclohexane

The dilute solution properties of linear polybutadienes with dimethylamine and zwitterionic end groups were studied by membrane osmometry (MO), low-angle laser light scattering (LALLS), viscometry, and dynamic light scattering (DLS) in cyclohexane. The polymers were prepared by anionic polymerization, under high vacuum conditions using [3-(dimethylamino)propyl]lithium as initiator. The dimethylamine groups were converted to zwitterions by reaction with cyclopropane sultone. No evidence of association was found for the amine-capped polymers, whereas the zwitterionic samples exhibited strong association in cyclohexane. The degrees of association increase by decreasing molecular weight of the base polymer due to the excluded volume repulsions. These aggregation numbers are of the same order as those found for ω-functionalized polyisoprenes, with the same polar groups in the same solvent. The hydrodynamic properties, measured by viscometry and dynamic light scattering, supported the conclusions drawn by LALLS and provide strong evidence that the aggregates behave hydrodynamically as star polymers. Comparison with theoretical models shows that the association behavior is best described by the linear head packing model. © 1996 John Wiley & Sons, Inc

Block copolymers of styrene and n-alkyl methacrylates with long alkyl groups. Micellization behavior in selective solvents

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 multi-molecular 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

Characteristic ratio of poly(tetrahydrofurfuryl acrylate) and poly(2-ethylbutyl acrylate)

The synthesis, characteristic ratio Cx and glass transition temperature (Tg) of poly(tetrahydrofurfuryl acrylate) (PTHFA) and of poly(2-ethylbutyl acrylate) (P2EBA) are reported. P2EBA has slightly lower flexibility (Cx = 9.2) than PTHFA (Cx = 8.6), mainly because of the higher bulkiness of its side group and the closer proximity to the main chain. The Cx results compared with the corresponding polymethacrylates show an increase in flexibility due to the absence of the α-methyl group. Comparison with poly(methyl acrylate) clearly shows the influence of the bulkiness of the side group on the chain flexibility. The lower Tg of P2EBA than that of PTHFA may be explained by the higher flexibility of the 2-ethylbutyl side group. © 1997 John Wiley & Sons, Inc

Block copolymers with crystalline/amorphous, crystalline/polyelectrolyte and amorphous/polyelectrolyte blocks

Diblock and triblock copolymers containing polybutadiene (PB) with high 1.4-butadiene content and poly(tert-butyl methacrylate) (PtBMA) blocks were synthesized by anionic polymerization using high vacuum techniques. These polymers were transformed by homogeneous hydrogenation, using the Wilkinson catalyst, into block copolymers containing a semicrystalline polyethylene (PE) block and an amorphous semiflexible PtBMA block. Subsequent hydrolysis resulted in block copolymers with semi-crystalline (PE) and polyelectrolyte (poly(methacrylic acid), PMAA) blocks. The PB/PtBMA copolymer precursors were also converted by direct hydrolysis to PB/PMAA copolymers, and subsequently to PB/poly(sodium methacrylate) amorphous/polyelectrolyte block copolymers by neutralization with NaOH. The extent of the transformation reactions was determined by solution and solid-state NMR spectroscopy. The materials containing a semicrystalline block were also characterized by differential scanning calorimetry (DSC). Some preliminary results from DSC on the phase behavior (mixing of phases and interplay between organization in the amorphous and semicrystalline phases) of these new materials are also presented

Statistical copolymers of styrene and 2-vinylpyridine with trimethylsilyl methacrylate and trimethylsilyloxyethyl methacrylate

Statistical copolymers of styrene with trimethylsilyl methacrylate, STMS, and trimethylsilyloxyethyl methacrylate, STME, and of 2-vinylpyridine with trimethylsilyloxyethyl methacrylate, VTME were prepared by free radical copolymerization in benzene with 2,2′-azobisisobutyronitrile, AIBN. The reactivity ratios of the different monomers were estimated using the Finemann-Ross, the inverted Finemann-Ross, and the Kelen-Tüdos or the extended Kelen-Tüdos graphical methods. Structural parameters of the copolymers were obtained by calculating the diad sequence fractions, which were derived using the monomer reactivity ratios. The results were compared with those obtained from the copolymerization of styrene and 2-vinylpyridine with methacrylic acid and 2-hydroxyethyl methacrylate. © 2004 Elsevier Ltd. All rights reserved

Hydrodynamic behavior of anionically prepared linear polyisoprenes and polystyrenes in carbon tetrachloride

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. Copyright © 1995 John Wiley & Sons, Inc