Polymer Segmental Motion Research Articles

Structure and dynamics of the branched polysaccharide scleroglucan in dilute solutions studied by 1D and 2D NMR spectroscopy

Variable temperature and magnetic field dependent 13C NMR relaxation measurements ( T 1 and NOE) were carried out for the branched polysaccharide scleroglucan in DMSO-d 6 dilute solutions. The relaxation data of the backbone carbons were analyzed quantitatively by using the bimodal time-correlation functions developed by Dejean, Lauprêtre, and Monnerie (DLM), which offered the best quantitative description of the segmental motion of the carbohydrate chains. Simple internal rotations of the free hydroxymethyl groups of the backbone rings about the exocyclic C-5–C-6 bonds superimposed on segmental motion have been described as a diffusion process of restricted amplitude. Multiple internal rotations involving the exocyclic hydroxymethyl group of the ring at the branched point and that of the side chain ring, as well as the side chain ring itself were described by employing a composite TCF for side chain motions superimposed on polymer segmental motions. These time-correlation functions and their Fourier transform pairs, the spectral densities, offered the best interpretation of the relaxation data of the exocyclic free hydroxymethyl groups, and the pendent d-glucorynosyl ring. Finally, the 1H- and 13C NMR spectra of the neutral scleroglucan in DMSO-d 6 were analyzed by employing a series of 2D NMR experiments. The 500 MHz 1H NMR spectrum of scleroglucan at 283 K show severe peak overlaps, which do not allow the complete assignment of all signals in the carbon spectrum.

Enhancement of ion transport in polymer electrolytes by addition of nanoscale inorganic oxides

The effect of addition of nanoparticle inorganic oxides to poly(ethylene oxide) (PEO) complexed with LiClO 4 on cation transport properties has been explored by electrochemical and 7 Li nuclear magnetic resonance (NMR) methods. The presence of the nanoparticles generally increases the ionic conductivity and the cation transference number, the effect being greatest for TiO 2. The enhancement in cation transference number is directly correlated with increased Li diffusivity measured by NMR. The NMR results also demonstrate that the increased ionic conductivity is not attributable to a corresponding increase in polymer segmental motion, but more likely a weakening of the polyether-cation association induced by the nanoparticles.

Local motions of polystyrene chain in semi-concentrated polymer solutions

In the 1980s, the mechanism of local motions of polymer chain was discussed theoretically and experimentally by many researchers. Finally, the intermittent motion model was proposed with respect to the measurements of emission anisotropy decay curves of a chromophore incorporated into a polymer main chain in dilute polymer solutions. The relationship between orientational auto-correlation function type based on power law and measured decay curves was discussed in these reports. The local motion of anthryl groups end-capped polystyrene (APSA) was measured in various polystyrene/di- n-butyl phthalate mixtures by using the fluorescence depolarization method. The intermittent motion model for local motions of polymer segments is modified in order to apply to both dilute and semi-concentrated polymer solutions. The model predicts that the orientational auto-correlation function will be given by the KWW function when the segment–solvent collision is effective on the relaxation process. On the other hand, the hyperbolic function will be observed when the segment–segment collision becomes effective. It was found that measured decay curves in dilute and concentrated polymer solutions were well represented by the KWW function and the hyperbolic function, respectively. The result implies the fact that modified intermittent motion model is in good agreement with the experimental data.

A comparison of neutron scattering studies and computer simulations of polymer melts

Neutron scattering and computer simulations are powerful tools for studying structural and dynamical properties of condensed matter systems in general and of polymer melts in particular. When neutron scattering studies and quantitative atomistic molecular dynamics simulations of the same material are combined, synergy between the methods can result in exciting new insights into polymer melts not obtainable from either method separately. We present here an overview of our recent efforts to combine neutron scattering and atomistic simulations in the study of melt dynamics of polyethylene and polybutadiene. Looking at polymer segmental motion on a picosecond time scale, we show how atomistic simulations can be used to identify molecular motions giving rise to relaxation processes observed in experimental dynamic susceptibility spectra. Examining larger length and longer time scale polymer dynamics involving chain self-diffusion and overall conformational relaxation, we show how simulation results can motivate experiment and how combined results of scattering and simulation can be used to critically test theories that attempt to describe melt dynamics of short polymer chains.

Dynamic mechanical response of polymer networks

The dynamic-mechanical response of flexible polymer networks is studied in the framework of the tube model, in the limit of small affine deformations, using the approach based on Rayleighian dissipation function. The dynamic complex modulus G*(ω) is calculated from the analysis of a network strand relaxation to the new equilibrium conformation around the distorted primitive path. Chain equilibration is achieved via a sliding motion of polymer segments along the tube, eliminating the inhomogeneity of the polymer density caused by the deformation. The characteristic relaxation time of this motion τe separates the low-frequency limit of the complex modulus from the high-frequency one, where the main role is played by chain entanglements, analogous to the rubber plateau in melts. The dependence of storage and loss moduli, G′(ω) and G″(ω), on crosslink and entanglement densities gives an interpolation between polymer melts and crosslinked networks. We discuss the experimental implications of the rather short relaxation time and the slow square-root variation of the moduli and the loss factor tan δ(ω) at higher frequencies.

A new approach to the understanding of ion transport in semicrystalline polymer electrolytes

Abstract Despite the conventional wisdom that ion transport in polymer electrolytes is mediated primarily by polymer segmental motion, we have performed measurements on semicrystalline complexes of poly(ethylene oxide) (PEO) with LiI which suggest that transport occurs preferentially along the PEO helical axis, at least in the crystalline phase. The principal basis for this claim is an observed enhancement by a factor of 5–20 in electrical conductivity in stretched polymer electrolyte films. The effect of uniaxial stress on the polymer electrolyte long and short range structures was investigated by X-ray diffraction and 7Li nuclear magnetic resonance (NMR) spectroscopy. Stretching results in partial alignment of the PEO helices and also induces small but observable changes in the Li+ solvation sheath. These results are correlated with the ionic conductivity enhancement in the stretched polymer.

Quantifying rubber degradation using NMR

Ageing can lead to the degradation of the tensile properties of natural rubber. The ageing process causes changes in the polymer segmental motion as well as the chemical structure, both of which can be monitored using nuclear magnetic resonance (NMR) spectroscopy. This work demonstrates that NMR can quantify rubber degradation due to ageing, and also that relatively simple NMR equipment can be used. This simpler equipment can be made portable and so could give a simple and fast indication of the condition of rubber in service. The 1H NMR transverse relaxation time, T 2, and the 13C NMR spectrum using cross polarization and magic angle spinning (CP MAS) for samples taken at various levels of a degraded natural rubber liner were compared. These experiments showed that, as the level of degradation increased, the 1H NMR transverse relaxation time decreased. The 13C spectra showed considerable peak broadening, indicative of decreased mobility with increased level of degradation as well as the presence of degradation products. Further investigations using lower powered NMR equipment to measure the 1H NMR transverse relaxation times of two different series of natural rubbers were also performed. This work has shown that this simpler method is also sensitive to structural and mechanical property changes in the rubber. This method of monitoring rubber degradation could lead to the non-destructive use of NMR to determine the condition of a part in service.

Ion conduction of poly[methoxy oligo (oxyethylene) propylene] synthesized by the Et(Ind)2ZrCl2-MAO catalyst

Poly[methoxy oligo (oxyethylene) propylene] was synthesized by means of the Et(Ind)2ZrCl2-MAO catalyst. The ionic conductivity of poly[methoxy oligo (oxyethylene) propylene] with the lithium salt depends on the content of the lithium salt. The temperature dependence of conductivity was determined and the Vogel–Tammann/Hesser–Fulcher (VTF) plot agreed well with theoretical values, confirming the influence of the polymer segmental motion on conductivity. The ionic conductivity as high as 10−4.7 s/cm can be obtained at room temperature, and this can be increased one or two orders of magnitude by blending the polyelectrolyte with hydroxyl-containing additives such as tetraethylene glycol. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1397–1400, 1999

Coordination Polymers Based on Bis(bipyridyl)alkane Ligands: Film Preparation and Charge-Transport Characteristics

Electroactive coordination polymers have been prepared by reacting Fe2+ and Co2+ with bis(bipyridyl)alkane (bba) ligand films that have been spin coated onto glassy carbon electrodes. The resulting films exhibit redox characteristics similar to those of electropolymerized vinyl(bipyridyl) metal complexes. The stability of the electrode-bound films increases as the length of the linking alkyl chain decreases. Better stability is also obtained with Fe2+ films than Co2+ films and with the alkyl-linking group attached at the 4-position rather than the 5-position. Charge-transport measurements using chronoamperometry have been conducted on poly-FeII/bba films in which the alkyl linker consists of 2, 4, and 6 methylene groups. Values of D1/2C (D = charge-transfer diffusion coefficient; C = concentration of redox sites) range from 9.5 × 10-8 to 2.3 × 10-8 mol/cm2 s1/2 at 298 K and follow a trend of decreasing D1/2C with increasing alkyl chain length for the 4-position−linked FeII/bba polymers. No such trend is observed for the analogous 5-position−linked systems. Activation parameters Ea and ΔH⧧ range from 22 to 31 kJ/mol, whereas ΔS⧧ ranges from −30 to −75 J/mol K. The results are consistent with a mechanism in which the increase in methylene chain length causes a decrease in the rate of charge transport due to the lower frequency of electron-transfer collisions between neighboring redox sites. However, polymer segmental motion is also believed to play a secondary role in this mechanism.

Neutron spin echo investigations of polymer dynamics

In 1997, the instrumental basis for neutron spin echo (NSE) investigations of polymer dynamics was considerably enlarged as new and improved spectrometers became available. The scientific highlights include NSE studies on the segmental motion of polymers with various chain architectures in the liquid as well as in the solid state and a direct comparison of NSE findings with the results of molecular dynamics simulations.

Electrical, thermal and NMR investigation of composite solid electrolytes based on PEO, LiI and high surface area inorganic oxides

High salt concentration polymer composite electrolytes, containing poly(ethylene oxide) (PEO), LiI and nanoscale Al 2O 3 or MgO and, in some cases, ethylene carbonate (EC) and poly(methyl methacrylate) (PMMA), were investigate by electrical conductivity, differential scanning calorimetry (DSC) and both wide-line and high resolution solid state 7Li NMR. The high resolution NMR spectrum of a sample with a PEO:Li ratio of 3:2 is consistent with at least two Li environments, one solvated by the polymer and one in small ionic clusters. A correlation between the observed change in Li environment at elevated temperature and a sudden increase in conductivity is suggested. All results demonstrate that the conduction mechanism in concentrated composite electrolytes is significantly different than in more dilute polymer electrolytes, in which the ion transport process is associated with polymer segmental motion.

Increased glass transition temperature in motionally constrained semicrystalline polymers

A large number of experimental results in the literature support and illuminate a model of behavior of chains and chain segments in the amorphous phase of semicrystalline polymers connecting the elevation of the glass transition temperature (Tg) above its normal value to several kinds of motional restrictions imposed on the chains and parts thereof. Accordingly, polymer chain, chain-segment and chain-fragment motions of all kinds comprise one or more torsions around main-chain bonds from one stable conformation to another, known as rotational isomerizations. When impediments are placed in front of thermal fluctuations and larger transversal and longitudinal motions of polymer chains, segments and shorter fragments in the amorphous phase, and the motions are thus restricted, the glass transition temperature is elevated relative to that of the same amorphous phase in the bulk under normal conditions. The obstructions may prevent either the onset of rotational isomerizations or of their completion once started. The completion of the torsional isomerizations and larger motions may be prevented by eliminating the free spaces necessary to accommodate the volumes of the interconverting chain fragments and segments even when they move in concert, or by preventing the creation of such free spaces. Another way to hinder the completion of such motions is by the introduction into the system of many rigid walls and other interfaces with strong attractive interactions with the polymer, that by geometrical constraints and attractive interactions suppress the rotational and larger motions and prevent their completion. Elimination of the necessary free volume is achievable by the application of compressive pressure, while the introduction of rigid attractive walls may be accomplished by the incorporation of crystallites, as in semicrystalline polymers, or by the addition of rigid finely comminuted foreign additives with very large surface areas or confining voids with high tortuosity. It is believed that motional restrictions imposed on the amorphous phase by the growth faces of polymer crystallites, especially in oriented semicrystalline polymers, are more effective than the restrictions imposed by the fold surfaces of these crystallites. The prevention of the onset of rotational isomerizations and larger motions may be achieved by stretching the polymer chains and chain segments in the amorphous phase and, by one means or another, pinning down the taut chains such that essentially all their rotational isomers are in the trans conformation: they cannot interconvert to the gauche conformation since it requires the chain’s end-to-end distance to decrease. Parallel alignment of relatively taut chain-segments may impose additional geometrical restrictions on both the onset and completion of rotational isomeric torsions and, of course, on longer-range motions. In all cases, the Tg of the motionally constrained parts of the amorphous phase, especially in semicrystalline polymers, is expected to rise. It is likely that the characteristic length associated with transversal motions and their suppression is Rc, the spatial distance between entanglements, which is of the same size scale, and may be the same as the tube diameter of the reptation model. Special emphasis was placed in this work on the semicrystalline polymers poly (ϵ-caprolactam) (nylon-6) and poly (ethylene terephthalate) (PET). © 1998 John Wiley & Sons, Ltd.

Poly(ethylene oxide) electrolytes containing mixed-alkali metal perchlorates

Impedance spectroscopy and differential scanning calorimetry studies have been performed for mixed-alkali systems of [(1- x)LiClO 4 + xMClO 4](PEO) 16 complexes (M = K, NH 4) with varying concentrations of x. At high temperatures above the melting temperature ( T m of poly(ethylene oxide) (PEO), the ionic conductivity exhibits no mixed-salt effect, revealing that there are no cation-cation interference effects as in the mixed-alkali glasses, in which a great reduction of the conductivity has been observed. However, the properties related to the phase formation exhibit the mixed-salt effect, showing a negative deviation of T m from additivity, the appearance of low-melting crystalline complexes and an increase in crystallinity. Hence, the conductivity below T m, which is directly related to the phase formation at ambient temperature, shows a small negative deviation from additivity, especially for Li + /NH 4 + systems. The conductivity changes due to mixing salts are discussed by two terms, i.e., changes in the crystallinity and in the polymer segmental motion.

ポリ（１‐トリメチルシリル‐１‐プロピン）膜の劣化現象

Polymeric membranes must have good permeabilities, permselectivities, and long-term stability, and be compatible with the process environment in which they will be used. However, polymers with high permeability tend to have low selectivity and vice versa. The glassy poly (1-trimethylsilyl-1-propyne) (PMSP) has the potential to be an important membrane gas separation material, due to the fact that it has the highest intrinsic gas permeability of all synthetic polymers known at present. The biggest problem with PMSP is the decrease in gas permeability with age. There has been an ongoing search for PMSP with superior separation and stability. Membrane contamination is a dominant factor effecting the gas permeability of PMSP ; and, in the absence of contaminants, aging is due to the relaxation of nonequilibrium excess free volume. PMSP has a glass transition temperature of more than 250°C. In the case of glassy polymers, small-scale polymer segmental motions cause a relaxation of nonequilibrium excess free volume and their physical properties drift over time. Because the PMSP membrane has a larger free volume compared to other glassy polymers, a dramatic decline in gas permeability occurred.

Micro-Brownian Motion of Polymer Segments in a Monolayer at the Air−Water Interface: A Time-Resolved Study of Intralayer Energy Transfer

This work is concerned with micro-Brownian motion of polymer segments on a water surface, which is observed as the lateral diffusion of fluorescence probes attached to the polymer chains. Poly(vinyl octanal acetal)s labeled with phenanthrene (P: energy donor) and anthracene (A: energy acceptor) are spread on water, yielding a stable monolayer in which the probes are able to take statistically random distributions in the two-dimensional plane. The time-resolved fluorescence analysis of the energy transfer between the P and A probes allows us to evaluate the acceptor densities and lateral diffusion coefficients of polymer segments on the water surface. The result is obtained by fitting the fluorescence decay data with the theoretical prediction by the Monte Carlo simulation. It is found that this polymer forms a viscous monolayer, in which the lateral diffusion of polymer segments takes place with a diffusion coefficient of ca. 8 × 10-8 cm2 s-1.

NMR studies of ionic mobility and molecular mobility in polymer electrolytes

The pulsed field gradient spin echo technique has been used to measure the self-diffusion coefficients of both the cation and anion in LiCF 3SO 3 PEO n systems as a function of concentration and temperature. In addition, the ionic conductivities were determined by ac conductivity measurements. The temperature dependence of both conductivity and ion diffusivities could be very well described by the Vogel-Tamman-Fulcher equation. Predicted values for ionic conductivity were obtained from the NMR diffusivities using the Nernst-Einstein equation and compared with those from direct measurement. It is clear that at higher reduced temperatures and/or lower salt concentrations, there is an increasing degree of ionic association or correlated motions of neighbouring cations and anions which give rise to deviations from the Nernst-Einstein equation. The molecular mobility of the polymer chains in these systems has also been studied by NMR measurements of the proton transverse relaxation behaviour. It has been found that the addition of salt does not affect the critical entanglement molecular weight of the polymer but it does increase the segmental relaxation time. Below the entanglement molecular weight the polymer chain dynamics can be described by the Rouse model. Above the critical entanglement molecular weight, a model due to Brereton can be used, and the NMR data have been shown to be consistent with a constant chain length between entanglements, the relaxation times varying with salt concentration in a manner predicted from the conductance measurements. It is concluded that the dissolved salt increases the energy barriers to polymer segmental motion, but not the entangled structure of the polymer.

A 13C NMR study of the role of plasticizers in the conduction mechanism of solid polymer electrolytes

The addition of low molecular weight solvents such as dimethyl formamide (DMF) and propylene carbonate (PC) to urethane crosslinked polyethers results in enhancement of polymer segmental motion, as determined in this work from polymer 13C spin lattice relaxation measurements ( T 1) and glass transition temperatures. The formation of salt-polyether complexes results in a decrease in T 1, even in the presence of the plasticizer, indicating that the polymer ether molecules are still involved in the alkali metal coordination. In a polymer electrolyte containing 1 mol kg −1 LiClO 4 the addition of DMF and PC have significantly different affects on the polymer mobility, although they both enhance the conductivity. The conductivity enhancement therefore is not solely the result of an increased solvent mobility.

Dynamically disordered hopping, glass transition, and polymer electrolytes

The central parameter of the dynamically disordered hopping (DDH) model, the renewal time, is correlated with the characteristic time constant of the glass transition relaxation in polymer–salt complexes. With this identification, the frequency-dependent permittivity of these materials can be quite adequately described. In particular, experimental evidence for a high-frequency relaxation predicted by the DDH model is presented. This relaxation corresponds to the polarization of ions in their local percolation clusters as they wait for a renewal event to occur. In light of information on the renewal time, the direct current properties of polymer–salt complexes are used to calculate the size of these local clusters. These calculations suggest that the motion of an ion in the absence of renewal (polymer segmental motion) corresponds to displacements within its local coordination ‘‘cage’’ rather than hopping between several available coordination sites.

A nuclear magnetic resonance study of toluene‐polyisobutylene solutions. 3. Spin‐lattice relaxation: Rotational and segmental motion

AbstractThe spin‐lattice relaxation times are determined for the methylene carbon of polyisobutylene (PIB), as well as for the ortho carbon of toluene in toluene‐polyisobutylene solutions. The Hall‐Helfand correlation function combined with restricted anisotropic rotational diffusion was used to treat the T1 data of the methylene carbon of PIB. A simple exponential correlation function was used to describe the local motion of toluene in the solutions which falls in the extreme narrowing limit for the solutions studied. Both models described satisfactorily the temperature and field dependence of the spin‐lattice relation times. From the temperature dependence of the correlation times for the polymer segmental motion, the free volume of the solution at each concentration is extracted and compared with the values obtained from previous studies of the translational motion of the toluene penetrant. The free volume values extracted from the T1 data for the methylene carbon of PIB and the self‐diffusion data for the toluene were found to be in substantial agreement. The interrelationship of the timescale of segmental motion of the polymer and the translational diffusion of the toluene was also examined and it was found that the two types of motion seem to be correlated in high polymer concentrated solutions. The toluene reorientational motion was found to be much faster than both the polymer segmental motion and the toluene translational diffusion leading to the conclusion that the toluene reorientational motion is uncoupled from these two motions. ©1995 John Wiley & Sons, Inc.

An analysis of ionic conductivity in polymer electrolytes

AbstractConductivities for a wide variety of ionically conducting polymer electrolytes with a range of salt compositions have been investigated over the temperature region Tg to 370 K. When the conductivity data are analyzed as a function of temperature using the empirical Vogel‐Tammann‐Fulcher (VTF) equation a common trend is observed in that deviations in the fits to the data invariably occur in the temperature range 1.2 Tg to 1.4 Tg for all of the samples investigated. This deviation is interpreted as a decoupling of the ions from polymer segmental motion. Recent 23Na NMR and 22Na positron annihilation studies of sodium salt‐based polymer electrolytes support this interpretation with evidence of a change in dynamics at about 1.2Tg. © 1994 John Wiley & Sons, Inc.