Local motion of the oligo-and polystyrene chain end in dilute solution was examined by the fluorescence depolarization method. The molecular weight of the sample varied from 5.1 × 10 2 to 2.5 × 10 4 . The relaxation time of local motion, Tm, in benzene solution increased with molecular weight and reached an asymptotic value at MW ) 2 × 10 3 with Tm = 0.3 ns. In ethyl acetate, which is a poorer solvent than benzene, Tm became constant at a higher molecular weight than in benzene, and the asymptotic relaxation time was longer than that in benzene. We proposed that the difference in the relaxation time and in its molecular weight dependence between the two solutions may result from the local potential for the conformational transition of the main chain bond, rather than the segment density. In comparison with the relaxation time for the polystyrene chain center, both the critical molecular weight and the asymptotic relaxation time for the chain end were about 1 order smaller than those for the chain center. This indicates that the mobility of a linear polymer chain end is sufficiently different from that of its chain center.

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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...

Concentrated solutions of cellulose and amylose were prepared with an ionic liquid 1‐butyl‐3‐methylimidazolium chloride (BmimCl), which was chosen as a good solvent for these polysaccharides. Dynamic viscoelasticity of the concentrated solutions was examined to obtain the molecular weight between entanglements, Me. The value of Me in the molten state (Me,melt), a material constant that reflecting the entanglement properties, was determined for cellulose and amylose by extrapolating Me to the “melt.” A marked difference in Me,melt was found: 3.2 × 103 for cellulose and 2.5 × 104 for amylose. The value of Me,melt for cellulose, which is composed of β‐(1,4) bonding of D‐glucose units, is very close to those for polysaccharides with a random‐coil conformation such as agarose and gellan in BmimCl. The much larger Me,melt for amylose can be attributed to the helical nature of the amylose chain, α‐(1,4)‐linked D‐glucose units. The effect of concentration on the zero‐shear viscosity for the solutions of cellulose and amylose was also examined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

The local chain dynamics of poly(oxyethylene) (POE) labeled with anthryl group in the middle of the main chain was examined by the fluorescence depolarization method. The relaxation time of the local motion was evaluated and its molecular weight dependence was shown. POE had a mean relaxation time in the order of subnanoseconds. The value of the relaxation time increased with the molecular weight in the range of MW < 4000 and reached an asymptotic value at MW of about 4000. The relaxation time and the activation energy for local motion of POE were compared with those of some styrene and methacrylate polymers and the characteristics of POE chain were discussed. POE had a much higher local chain mobility than other polymers. This high local chain mobility of POE results from the molecular structure of POE chain.