Seigou Kawaguchi

Aqueous solution properties of oligo- and poly(ethylene oxide) by static light scattering and intrinsic viscosity

Abstract Conformational properties of ethylene glycol, oligo-, and poly(ethylene oxide) ranging in weight-average molecular weight ( M w ) from 62 to 1.1 × 10 7 have been studied by static light scattering and viscometry in salt-free and 0.45 M K 2 SO 4 water and in benzene. Above M w = 6 × 10 3 , intrinsic viscosity ([η]) and z -average square radius of gyration (〈 S 2 〉 2 ) of PEO in a salt-free solution at 25°C, [η] = 4.33 × 10 −4 M w 0.67 9 dl g −1 and 〈 S 2 〉 z = 4.08 × 10 −18 M w 1.1 6 cm 2 , respectively. The second virial coefficient is positive in water at 25°C but one order of magnitude smaller than reported by Devanand et al. ( Macromolecules , 1991, 24 , 5943). A θ-temperature for PEO in 0.45 M K 2 SO 4 aqueous solution is determined to be 34.5°C and above M w = 4 × 10 2 , [η] and 〈 S 2 〉 z follow the power laws for an unperturbed polymer chain. The characteristic ratio ( C ∞ ) of PEO is 5.2 ± 0.1. 9.3Awas determined for the persistence length and 8.7A −1 for the molar mass per unit contour length of a PEO chain, based on the helical wormlike touched-bead model. The PEO chain in water behaves as a flexible polymer with a relatively large hydrodynamic diameter (9A) because of the hydration of the PEO chain.

Poly(macromonomers): Homo- and Copolymerization

Syntheses and characterization of branched polymers prepared by homo- and copolymerization of macromonomers are reviewed. A number of macromonomers have so far been available as potential building blocks to design a variety of well-defined, branched homo- and copolymers including comb, star, brush, and graft types. Recent progress in macromonomer syntheses, macromonomers’ homo- and copolymerization, characterization of the branched polymers obtained, as well as application to design of polymeric microspheres are described. Macromonomers and their homo- and copolymerization appear to provide continuing interest in designing and characterizing a variety of branched polymers and in their unique applications.

Macromolecular surfactant as a pseudo-stationary phase in micellar electrokinetic capillary chromatography

We examined polymers of sodium 11-acrylamidoundecanoate [poly(Na 11-AAU)] with a very high molecular mass (>10(6)) for their potential use as a pseudo-stationary phase in micellar electrokinetic capillary chromatography (MEKC). Size-exclusion chromatography and capillary electrophoresis studies reveal that the polymers are highly charged, and have a densely packed chain structure. For aromatic compounds, the polymeric surfactant showed significantly different selectivity than sodium dodecyl sulfate (SDS). It was suggested that one molecule of poly(Na 11-AAU) forms one micelle. The structural stability of this pseudo-stationary phase permitted its use with relatively high percentages of organic modifiers in the buffer medium, allowing the separation of highly hydrophobic compounds which are difficult to analyze by conventional MEKC with SDS.

Conformation of poly(methacrylic acid) in acidic aqueous solution studied by small angle X-ray scattering.

The nature of the contracted form of poly(methacrylic acid) PMA chain in salt-free acidic aqueous solution was studied by analyzing scattering curves registered by small-angle X-ray scattering, comparing it with those of PMA in methanol at 26 degrees C and of partially neutralized PMA in aqueous solution containing added salt (the concentration of added salt, Cs=0.1 M NaF). It is shown that the distribution of segments in the contracted form as well as that of PMA in methanol is that of a random-coil in a theta medium and that this distribution of segments is stable over a fair range of degrees of ionization alpha for Cs below 0.1 M. Moreover, the persistence length of PMA at Cs=0.1 M (4+/-0.5 A) is substantially constant throughout the entire range of alpha, indicating that the contracted form of PMA changes to an expanded random-coil in a higher pH region without a significant change in the chain flexibility.

Effect of sonication on nitroxide-controlled free radical polymerization of styrene.

Effect of sonication on the autopolymerization of styrene in the presence of 2,2,6,6-tetramethylpiperidinyl-1-oxy as the mediating radical was investigated at 110-135 degrees C. The thermal polymerization under sonication proceeded in the manner of a living radical polymerization to afford well-defined polystyrene. The sonication was found to decrease the induction period and increase the polymerization rate.

Dispersion (co)polymerization of styrene in polymeric media to prepare polymer micro blends

In general, different polymers are not compatible with each other so that their mixture usually segregates to result in macroscopic phase separation. In order to achieve microscopic polymer blending, dispersion polymerization in a polymeric medium appears an interesting approach. We have attempted styrene polymerization in poly(ethylene glycol) (PEG) and in poly(dimethylsiloxane) (PDMS) with the corresponding macromonomers as reactive (copolymerizable) dispersants. Fine, monodispersed polystyrene microspheres have been prepared in the polymeric media with relatively low molecular weights, but not in those with high molecular weights due to extensive particle aggregation. So, monodisperse polystyrene latex (Dn = 0.70 μm), prepared by dispersion copolymerization in PDMS-diol (MW = 7,500) with a PDMS macromonomer, was allowed together with trimethylolpropane to react with hexamethylene diisocyanate using dibutyltin dilaurate as a catalyst. The final product after the polyaddition was a tough elastomeric composite with polystyrene particles finely dispersed and strongly anchored in PDMS-polyurethane matrix, as judged from SEM, DSC, and TGA measurements.

Aqueous solution behavior of amphiphilic poly(ethylene oxide) comblike polymers

Abstract The dilute aqueous solution behavior of regular amphiphilic comblike polymers with a polystyrene main chain and poly(ethylene oxide) (PEO) side chains, prepared by micellar polymerization has been investigated by means of multi-angle laser light scattering-size exclusion chromatography (MALLS-SEC), pyrene partitioning, and fluorescence spectroscopy. In 0.05 N NaCl solution, double logarithmic plots of 〈S2〉z1/2 of the comblike polymers with PEO chain length, n=50 against Mw were found to be fitted by a smooth curve convex upward. The slope of the curve was about 0.87 for Mw between 4×105 and 1×106 and about 0.56 for Mw higher than 2×107. The experimental Mw-dependence of 〈S2〉z and particle scattering factor, P(θ) were quantitatively described by a wormlike chain model with persistence length, q=16.8 nm. The persistence length of the comblike polymers was found to linearly increase with increasing PEO chain length.

Control of Particle Size in Dispersion Polymerization Using Poly(Ethylene Oxide) Macromonomers

Dispersion copolymerization of styrene with a small amount of PEO macromonomer having p-styrylbutyl end group (Mn = 2000) in methanol/water (90/10 vol%) produced monodisperse microspheres of 0.5 to 3 μ in diameter. The particle size increased in proportion to Θ l/3 W o 2/3 (r1/W Do S crit ) 1/2 , a theoretical model based on particles formation sterically stabilized by graft-copolymerized PEO chains on the particle surface, where Θ = styrene conversion, W o = styrene weight in feed, W Do = macromonomer weight in feed, S crit = critical occupancy area per grafted PEO chain, and r 1 = monomer reactivity ratio of styrene before critical conversion. Quantitave agreement between theory and experiment was obtained with S crit /r 1 = 10 nm 2 .

Photo‐initiated post‐polymerization in micellar system of amphiphilic poly(ethylene oxide) macromonomers

Aqueous micellar polymerization of amphiphilic poly(ethylene oxide) macromonomers carrying p-vinylphenylheptyl end-group has been found to persist to proceed after turning-off of the UV-irradiation. Simulation of the kinetics revealed a high propagation rate constant coupled with a low termination constant, supporting a living-like polymerization at the initial stage. Micellar copolymerization with equimolar styrene also proceeded after UV-irradiation. Polymer molecular weights in MALLS-SEC were also found to evolve with time after irradiation.