Abstract:Solution properties of near-monodisperse poly(a-methylstyrene) chains in the moderate solvent n-butyl chloride were investigated by a combination of static and dynamic light scattering and intrinsic viscosity measurements. These data allow the determination of the radii of gyration (Ro) as well as equivalent sphere radii: the hydrodynamic radius (RH), the viscometric radius (Rv), and the thermodynamic radius (RT) (defined below). Ratios of these various radii allow a comparison between solution properties of p… Show more
“…Strictly linear concentration dependencies were observed in the LALLS experiments implying an absence of aggregation (see Figure as an example). Furthermore, the molecular weights measured under sub-ϑ conditions (Table ) are in agreement with values measured previously for the same samples in good solvents. , Very strong molecular weight dependencies are observed at each temperature below ϑ for the PαMS/cyclohexane system as follows: 4 Plot of KMX-6 LALLS data for PαMS 475K.…”
Section: Resultssupporting
confidence: 88%
“…Furthermore, the molecular weights measured under sub-Θ conditions (Table 5) are in agreement with values measured previously for the samples in good solvents. 22,23 Very strong molecular weight dependencies are observed at each temperature below Θ for the PRMS/cyclohexane system as follows:…”
Classical and low-angle laser light-scattering
experiments were performed to measure the
second virial coefficient, A
2, and radius of
gyration, R
g, of linear
poly(α-methylstyrene) (PαMS) in the
poor solvent cyclohexane. The molecular weights,
M
w, of the polymers used cover the range of
60 000−3 500 000, and all samples have narrow molecular weight distributions.
The experimental temperatures
are controlled down to about 16 °C below the ϑ temperature (36.2
°C). At this temperature, the scaling
exponent of R
g with M
w is
0.414; this appears to be the lowest exponent ever reported for linear
chains
of synthetic polymers in solution. A strong molecular weight
dependence of the measured A
2 values
for
this PαMS/cyclohexane system is observed. These results are
compared with the predictions of available
theories and with other experimental results.
“…Strictly linear concentration dependencies were observed in the LALLS experiments implying an absence of aggregation (see Figure as an example). Furthermore, the molecular weights measured under sub-ϑ conditions (Table ) are in agreement with values measured previously for the same samples in good solvents. , Very strong molecular weight dependencies are observed at each temperature below ϑ for the PαMS/cyclohexane system as follows: 4 Plot of KMX-6 LALLS data for PαMS 475K.…”
Section: Resultssupporting
confidence: 88%
“…Furthermore, the molecular weights measured under sub-Θ conditions (Table 5) are in agreement with values measured previously for the samples in good solvents. 22,23 Very strong molecular weight dependencies are observed at each temperature below Θ for the PRMS/cyclohexane system as follows:…”
Classical and low-angle laser light-scattering
experiments were performed to measure the
second virial coefficient, A
2, and radius of
gyration, R
g, of linear
poly(α-methylstyrene) (PαMS) in the
poor solvent cyclohexane. The molecular weights,
M
w, of the polymers used cover the range of
60 000−3 500 000, and all samples have narrow molecular weight distributions.
The experimental temperatures
are controlled down to about 16 °C below the ϑ temperature (36.2
°C). At this temperature, the scaling
exponent of R
g with M
w is
0.414; this appears to be the lowest exponent ever reported for linear
chains
of synthetic polymers in solution. A strong molecular weight
dependence of the measured A
2 values
for
this PαMS/cyclohexane system is observed. These results are
compared with the predictions of available
theories and with other experimental results.
“…This parameter includes the ratio of the micellar radii obtained from viscosity measurements and DLS: 60 β MFS = 9.80 × 10 6 mol -1/3 for a hard impermeable sphere (since R v / R H = 1). For linear polymers, the theoretical β MFS values are 10.49 × 10 6 mol -1/3 for nondraining chains in good solvent ( R v / R H = 1.03) and 10.10 × 10 6 mol -1/3 for unperturbed chains (ϑ condition) ( R v / R H = 1.07). , The experimental β MFS values obtained in this work are (9.96 ± 0.07) × 10 6 (I 0 -24 micelles) and (9.82 ± 0.05) × 10 6 mol -1/3 (mixed micelles). Both β MFS values are closer to the value expected for hard spheres.…”
In acetonitrile, polyisoprene-b-poly(methyl methacrylate) (PI-PMMA) diblock copolymers form starlike micelles with a dense core of the insoluble PI blocks and a soft solvent-swollen corona of the soluble PMMA blocks. Static and dynamic light scattering experiments in combination with viscosity measurements show that these micelles behave hydrodynamically as hard spheres. The block copolymers are labeled at the block junction, with a single fluorescent dye, either a donor chromophore (phenanthrene) or an acceptor chromophore (anthracene). These dyes are confined to the interface during self-assembly. Fluorescence energy-transfer experiments on molecularly mixed micelles of donor-and acceptor-labeled copolymers provide a core radius of 7.6 ( 0.8 nm and a number-average aggregation number (N n agg ) of 98 ( 22 under the assumption that the energy transfer takes place on a surface of a sphere. Simulations in terms of a Helfand-Tagami junction distribution profile confirm that the core-corona interface of the PI-PMMA micelles is thin (ca. 0.9 nm) and that almost all of the energy transfer occurs within a narrow interfacial region. From the static light scattering measurements of the mixed micelles a weight-average aggregation number (N w agg ) of 127 ( 6 is obtained. The ratio N w agg /N n agg ) 1.3 agrees with size polydispersity of the micelles obtained from the analysis of dynamic light scattering data. The experimental corona thicknesses are in good agreement with those calculated from expressions describing starlike block copolymer micelles.
“…Previously, however, for PS in another thermodynamically moderate solvent, n-butyl chloride, we found Ry/Rn = 1.16 ± 0.04.19 Furthermore, for the system poly(a-methylstyrene)/n-butyl chloride (another polymer/moderate solvent system) we find Ry/Rn -1.18 ± 0.01. 20 In addition, for linear polybutadiene in good and solvents Ry/Rn values of 1.17 and 1.13, respectively, have recently been reported by Hoovers and Martin,21 whereas Fetters and co-workers22 have found Ry/Rn = 1.05 ± 0.03 for polyisobutylene in good, moderate, and solvents. Clearly, these findings suggest that the parameter Ry/Rn, which would be unity for a true hard sphere, is much more sensitive to the nature of the polymer and solvent than previously considered.…”
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