Fluorescence Depolarization Study of Local Motions in Polymers at the ϑ Temperature

Abstract

The mean relaxation times, T m's, of four different polymers measured by the fluorescence depolarization method were compared at their ϑ temperatures. These polymers, i.e., cis-polyisoprene (cis-PI), polystyrene (PS), poly(α-methylstyrene) (PαMS), and syndiotactic poly(methyl methacrylate) (s-PMMA), were labeled with anthracene in the middle of the main chain by living anionic polymerization. The ϑ temperature is a standard point without an excluded volume effect, and the ϑ temperature of these four polymers are almost the same, 34−35 °C. Therefore, the comparison of the T m's at the ϑ temperature enables us to clarify the relationship between the chain local motion and the chemical structure. The order of the reduced relaxation times, T m/η, was T m/η(cis-PI) < T m/η(PS) < T m/η(PαMS) < T m/η(s-PMMA), and the order of activation energies, E*, was E*(cis-PI) < E*(PS) < E*(PαMS) < E*(s-PMMA). From a molecular standpoint, the relaxation times depend on both the substituents attached to the main chain and the stereoregularity of the polymer chains. In consideration of the stereoregularity of the polymer chains, the relaxation time of atactic PαMS is estimated to be not much different from the relaxation time of atactic PMMA.

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

“…The quality of these solvents for PS was obtained by the intrinsic viscosity measurement. 17 Benzene = 1.66) was a better solvent than ethyl acetate = 1.12). In preparing the sample solutions, each polymer concentration was kept less than 10-5 M. Each solution was put into a quartz cell and degassed.…”

“…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][16][17][18][19][20][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.…”

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

“…We have examined the local chain dynamics of various polymers in dilute solution by the fluorescence depolarization method. [9][10][11][12][13][14] So far we have concentrated our attention on the center of the main chain. We have compared the local chain mobility between polymers, which differ in molecular structure 9,10,12 or stereoregularity.…”

Influence of a Fluorescent Probe on the Local Relaxation Times for a Polystyrene Chain in the Fluorescence Depolarization Method

“…The relaxation time of the probe was estimated through the measurements of the decay of the fluorescence anisotropy ratio. The local motion of polymer chain has been extensively studied for the polymers with the fluorescent probe labeled in the main chain. − We examined the local motion of polymer chains labeled with anthracene as the fluorescent probe in dilute solutions and discussed the effects of several molecular factors such as solvent condition, , molecular structure of polymer, − molecular weight, − and the position along a chain on the local chain mobility . However, there still remain some questions to be solved.…”