Local Motion of Oligo- and Polystyrene Chain End Studied by the Fluorescence Depolarization Method

Horinaka, Jun‐ichi; Maruta, M.; Ito, Shinzaburo; Yamamoto, Masahide

doi:10.1021/ma9814649

Cited by 29 publications

(44 citation statements)

References 40 publications

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“…The studies on the local motion of oligo-and polystyrene chain ends which supports this explanation more definitely will be reported separately. 33 The objection may be raised that our scheme supposing the difference in the potential energy between two solvents, in benzene and in ethyl acetate, is inconsistent with Abe's findings that the dimensions and conformations may be the same under the two solvent conditions in xw < 20. This can be explained by the fact that the unperturbed chain dimension is not independent of solvent and temperature.…”

Section: Relaxation Timecontrasting

confidence: 56%

Molecular Weight Effect on Local Motion of Polystyrene Studied by the Fluorescence Depolarization Method

Horinaka

Aoki

Ito

et al. 1999

Polym J

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ABSTRACT:The molecular weight effect on the local motion of polystyrene (PS) was examined in dilute solutions by the fluorescence depolarization method. Four PS samples with the fluorescent probe, anthryl group, in the middle of the main chain were synthesized by the living anionic polymerization. The molecular weight of samples varied from ca. 6.4 x 10 3 to 9.2 x 10 4 Solvents were benzene, a good solvent and ethyl acetate, a poor solvent. In both solvents, the relaxation time increased with the molecular weight up to MW = 10 4 at which it reached an asymptotic value. The activation energies were also estimated from the temperature dependence of the relaxation time, and its molecular weight dependence appeared to be similar to that of the relaxation time. It was suggested that the relaxation time of the local motion is determined by the potential for the conformational transition of main chain bonds, rather than by the segment density. Finally, the molecular weight effect on the relaxation time for PS was compared with that for poly(oxyethylene) (POE The flexible polymer chain in dilute solution has various motional scales with regard to time and space resulting from its high degree of intramolecular freedom. Because this chain dynamics governs a variety of properties of polymers, extensive experimental and theoretical efforts have been made to understand the polymer chain dynamics. 1 -21 For the local motion, which is fairly a fundamental process in chain dynamics, many experimental methods have been utilized, e.g., NMR, 5 -7 ESR, 8 dielectric relaxation, 9 -11 dynamic light scattering, 12 • 13 neutron scattering, 14 and fluorescence depolarization.15-21 The fluorescence depolarization method provides direct information about the local motion of polymer chains through a fluorescent probe that is covalently bonded to the polymer main chain. By using this method, we have examined the influence of molecular structure/ 6 · 19 stereoregularity, 17 and quality of solvent16·18 on the chain dynamics of a variety of polymers.The local chain dynamics in dilute solution is influenced by the molecular weight of the polymer in addition to those factors mentioned above. Concerning the fluorescence depolarization study, Waldow et a!. have examined the molecular weight effect on polyisoprene (PI) chain dynamics and concluded that the chain dynamics is governed by the segment density in the vicinity of the fluorescent probe labeled in the middle of the main chain. 21 Previously, we reported the molecular weight effect for poly( methyl methacrylate) samples and explained the behavior of the local chain dynamics by the segment density as well. 19 We also have reported the local chain dynamics of poly(oxyethylene) (POE) in good solvents and discussed the molecular weight effect. 20The static and dynamic properties of polystyrene (PS), a common polymer, have been widely studied. 2 · 6 -9 • 16 · 17 We have reported the effects of the solvent quality on the local dynamics of PS 17 and discussed the difference t To whom correspondenc...

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Section: Relaxation Timecontrasting

confidence: 56%

Molecular Weight Effect on Local Motion of Polystyrene Studied by the Fluorescence Depolarization Method

Horinaka

Aoki

Ito

et al. 1999

Polym J

Self Cite

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“…According to this procedure, an ideal blob would be made of 75 styrene units with an associated excimer formation rate constant k diff of 1.0 × 10 7 s -1 and an exchange rate k e [blob] of 4.5 × 10 6 s -1 . Interestingly this ideal blob size is similar to the size of a polymer chain for which a segment located at its center is no longer affected by the faster dynamics of the chain ends . Further studies will establish how the parameters 〈 n 〉, k diff , and k e [blob] vary with the nature of the solvent and the monomer structure, and they will lead to a better understanding of the folding mechanisms of synthetic and biological polymers.…”

Section: Discussionmentioning

confidence: 86%

“…Interestingly this ideal blob size is similar to the size of a polymer chain for which a segment located at its center is no longer affected by the faster dynamics of the chain ends. 20 Further studies will establish how the parameters 〈n〉, k diff , and k e [blob] vary with the nature of the solvent and the monomer structure, and they will lead to a better understanding of the folding mechanisms of synthetic and biological polymers.…”

Section: Discussionmentioning

confidence: 99%

A Blob Model To Study Chain Folding by Fluorescence

1999

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Monodisperse polystyrenes (M w/M n < 1.15) with molecular weights of 6K, 40K, and 110K and one polydisperse polystyrene (M w/M n = 1.5) with a molecular weight of 110K were synthesized. The chromophore pyrene was randomly and covalently attached onto the polymers. The dynamics of the chains were investigated quantitatively by monitoring the fluorescence of the pyrene monomer. The polymer coil was divided into several blobs among which pyrene is randomly distributed according to a Poisson distribution. The kinetics of the pyrene groups are monitored by only three parameters: k diff, the rate at which one excited pyrene encounters one ground state (GS) pyrene inside a blob; k e[blob], the product characterizing the exchange of GS pyrene between blobs (k e is the rate of exchange and [blob] is the blob concentration inside the polymer coil); and 〈 n〉, the average number of GS pyrene per blob. We show that the parameters retrieved by this analysis are internally consistent within the theoretical framework of the blob model. A critical polymer chain length is found above which polymer chain dynamics behave in a similar manner, regardless of the size of the polymer. Below the critical polymer chain length, chain dynamics are chain length-dependent.

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“…We have seen from the 1/V histograms that the Voronoi polyhedron volume is related to the topology of atoms: The volume associated with end atoms is larger than that associated with internal and junction atoms. Clearly, the motion of internal atoms is restricted by the connection on both sides, while ends are less restrictive 42 and move easily. The largest volume and the prominent microscopic thermal expansion of ends reflect the highest mobility.…”

Section: Discussionmentioning

confidence: 99%

Voronoi space division of a polymer: Topological effects, free volume, and surface end segregation

Tokita¹,

Hirabayashi²,

Azuma³

et al. 2004

The Journal of Chemical Physics

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In order to investigate the topological effects of chain molecules, united-atom molecular dynamics simulations of a 500-mer polyethylene linked by 50 hexyl groups (a grafted polymer having 52 ends) are carried out and analyzed in terms of Voronoi space division. We find that the volume of a Voronoi polyhedron for a chain end is larger than that for an internal or junction atom, and that it is the most sensitive to temperature, both of which suggest higher mobility of chain ends. Moreover, chain ends dominantly localize at the surface of the globule: The striking evidence is that while the ratio of surface atoms is only 24% of all atoms, the ratio of ends at the surface is 91% out of all ends. The shape of Voronoi polyhedra for internal atoms is prolate even in the bulk, and near the surface it becomes more prolate. We propose the concept of bonding faces, which play a significant role in the Voronoi space division of covalently bonding polymers. Two bonding faces occupy 38% of the total surface area of a Voronoi polyhedron and determine the prolate shape.

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Local Motion of Oligo- and Polystyrene Chain End Studied by the Fluorescence Depolarization Method

Cited by 29 publications

References 40 publications

Molecular Weight Effect on Local Motion of Polystyrene Studied by the Fluorescence Depolarization Method

Molecular Weight Effect on Local Motion of Polystyrene Studied by the Fluorescence Depolarization Method

A Blob Model To Study Chain Folding by Fluorescence

Voronoi space division of a polymer: Topological effects, free volume, and surface end segregation

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