Fluorescence Depolarization Study on Local Motions of Anthracene-Labeled Poly(alkyl methacrylate)s in Dilute Solutions and Evaluation of Their Chain Stiffness

Abstract

ABSTRACT:Samples of Poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(isopropyl methacrylate) (PiPMA) labeled with anthracene in the middle of the backbone chain were synthesized, and their local motions in dilute solutions were investigated by the fluorescence depolarization technique. Both the static stiffness parameter s-[ and the mean relaxation time T m as a measure of the dynamic chain stiffness were evaluated from the time-resolved data of fluorescence anisotropy ratio, and a correlation between these two parameters was found. Conformational energy calculations were performed for the diad compounds of PMMA, PEMA, and PiPMA, and then, the characteristic ratios were calculated according to the rotational isomeric state (RIS) model. The static chain stiffness parameter l-[ was obtained for the above three polymers as an independent evaluation of the static chain stiffness by a comparison between the RIS model and the helical wormlike chain model established by Yamakawa and his co-workers, and a correlation between ;.-1 and Tm was also found. The conformational character of PiPMA is remarkably different from that of PMMA and PEMA, resulting in greater chain stiffness for PiPMA than for PMMA and PEMA.KEY WORDS Fluorescence Depolarization / Anthracene-Labeled Poly-(methyl methacrylate) / Anthracene-Labeled Poly(ethyl methacrylate) / Anthracene-Labeled Poly(isopropyl methacrylate) / Local Motions / Conformational Energy Calculation / RIS Model/Chain Stiffness / Recently, local chain dynamics of flexible polymers has been studied in detail by the fluorescence depolarization technique as well as by other experimental tools. An advantage of the fluorescence depolarization method lies in the direct observation of the time-dependent orientation auto-correlation function (second order) of a finite bond vector, when the sample polymer is labeled with anthracene group in the middle of the backbone chain. This method provides a critical comparison between theory and experiment, and therefore, diagnostic information for the theory can be obtained.Viovy et af.1 tested various theoretical models for the local chain dynamics by the fluorescence depolarization measurements on anthracenelabeled polystyrene in dilute solutions. Recently, we investigated the local motions of anthracene-labeled poly(methyl methacrylate) (PMMA) in some solvents.2.3 Our previous result 3 showed that the local conformational motions belonging to the low-friction limit of Kramers can be well explained by the discrete models in which the discrete motional modes are taken into account.On the other hand, various theoretical approaches have been developed to understand the local conformational relaxations of polymer chains. These approaches may be divided into two types. The first type is to simulate a real polymer chain by a fairly simplified (idealized) model with some characteristic parameters which can be determined experimentally (phenomenological parameters). The 103

Correlation between fragility and cooperativity in segmental dynamics of glass-forming para-substituted polystyrenes

“…38 It has been revealed that dynamic stiffness (segmental relaxation time) increases generally as static chain stiffness increases in dilute solutions. 39,40 Figure 5 shows the WAXS profiles for the present PS derivatives. It is known that polystyrene exhibits two dominant halos at around s = 7.1 and 13.5 nm -1 [s = (4π/λ) sin θ].…”

Chain Dynamics of Styrene Polymers Studied by the Fluorescence Depolarization Method

“…The relaxation time became longer in the order of poly (ethyl methacrylate) ( ), poly(methyl methacrylate) (PMMA), and poly (iso-propyl methacrylate) (PiPMA). 18 The dynamic chain stiffness showed a parallel relationship with the static chain stiffness, and the chain stiffness depended on both the bulkiness of the alkyl residue and the chain tacticity (racemo fraction). For the local motion of the polystyrenes, the activation energy was larger in poor solvents than in good solvents.…”

Picosecond laser photolysis studies on photoinduced electron transfer processes in poly(1-vinylpyrene) in solutions

“…( 1)-(3). Since the time constant of the micro-Brownian motion in the polymer chain leading to the local conformation change is reported to be of the order of sub-nanoseconds-nanoseconds in the solution phase, [32][33][34][35] the present value of k DM suggests that the dimer cation formation was actually accompanied by a local geometrical change to result in a favorable conformation of the dimer cation. Summarizing the above results and discussion, it is concluded that the electron transfer dynamic behaviors of the PVPy-TCNB system in chloroform solution is represented not by the simple model based on Scheme 1 but by the biexponential decay process shown in Scheme 2.…”