Molecular Motions In Poly Research Articles

Local motions in poly(ethylene-co-norbornene) studied by 1H NMR relaxometry

Molecular motions in poly(ethylene-co-norbornene) were studied in a temperature range well below its glass transition point by a few techniques based on the NMR phenomenon. Temperature dependencies of proton spin-lattice relaxation times T1 (at 200MHz and at 30.2MHz), proton spin-lattice relaxation time in the rotating frame T1ρ (at 68kHz) and frequency dispersion of proton spin-lattice off-resonance relaxation times in the rotating frame T1ρoff were determined for the copolymer. Analysis of 1H NMR relaxation data permitted characterization of local motions occurring in the copolymer i.e. rotation of methyl groups around C3 axes, reorientations of methylene groups and motions of segments of polymer chains including norbornene groups.

Molecular motion and relaxation below glass transition temperature in poly (methyl methacrylate) studied by positron annihilation

In this paper, we present the study of local molecular motions in poly (methyl methacrylate) (PMMA) below glass transition temperature by measuring the ortho-positronium (o-Ps) intensity. Two series of experiments were performed: (1) the PMMA sample was irradiated by 22Na positron source with elongated time at room temperature, 225 K and 16 K, respectively, and positron lifetime spectra were measured as a function of irradiation time and (2) Positron lifetime and Doppler broadening spectra were measured as a function of temperature from 16 to 350 K after positron irradiation at 16 K for more than 350 h. While the o-Ps lifetime always shows no change with elapsed time, decrease and increase of o-Ps intensity I3 are observed at 225 K and 16 K, which are interpreted as the result of positron irradiation-induced free radicals and trapped electrons, respectively. With temperature increasing from 16 K, there is a continuous drop of I3 beginning at around 100 K. This is due to some local group movements such as the ester and main chain methyl group rotations, which lead to the detrapping of accumulated electrons. These local motions do not need additional free volume, so we observed no change of the o-Ps lifetime. Some other structural relaxations such as β-relaxation are also observed and discussed.

Influence of Crystallinity in Molecular Motions of Poly(l-lactic acid) Investigated by Dielectric Relaxation Spectroscopy

Specimens of poly(l-lactic acid) (PLLA) with 0.43 ≤ χc ≤ 0.65 were dielectric characterized. The relaxation process associated to the dynamic glass transition shifts to higher frequencies/lower tem...

Spinodal decomposition as a probe to measure the effects on molecular motion in poly(styrene-co-acrylonitrile) and poly(methyl methacrylate) blends after mixing with a low molar mass liquid crystal or commercial lubricant

The effects on molecular motion observed through early stage phase separation via spinodal decomposition, in melt mixed poly(styrene-co-acrylonitrile) (SAN) containing 25% by weight of acrylonitrile (AN) and poly(methyl methacrylate) (PMMA) (20/80 wt%) blends after adding two low molar mass liquid crystals (CBC33 and CBC53) and two lubricants (GMS and zinc stearate) were investigated using light scattering techniques. The samples were assessed in terms of the apparent diffusion coefficient ( D app ) obtained from observation of phase separation in the blends. The early stages of phase separation as observed by light scattering were dominated by diffusion processes and approximately conformed to the Cahn–Hilliard linearised theory. The major effect of liquid crystal (LC) was to increase the molecular mobility of the blends. The LC generally increased the Cahn–Hilliard apparent diffusion coefficient, D app , of the blend when added with concentrations as low as 0.2 wt%. GMS and zinc stearate can also improve the mobility of the blend but to a lesser extent and the effect does not increase at higher concentration. On the other hand, the more LC added, the higher the mobility. In all systems the second derivative of the Gibbs free energy becomes zero at the same temperature. The improved mobilities therefore seem to arise from changes in dynamics rather than thermodynamic effects.

Spinodal decomposition as a probe to measure the effects on molecular motion in poly(styrene-co-acrylonitrile) and poly(methyl methacrylate) blends after mixing with a low molar mass liquid crystal or commercial lubricant

The effects on molecular motion observed through early stage phase separation via spinodal decomposition, in melt mixed poly(styrene-co-acrylonitrile) (SAN) containing 25% by weight of acrylonitrile (AN) and poly(methyl methacrylate) (PMMA) (20/80 wt%) blends after adding two low molar mass liquid crystals (CBC33 and CBC53) and two lubricants (GMS and zinc stearate) were investigated using light scattering techniques. The samples were assessed in terms of the apparent diffusion coefficient ( D app) obtained from observation of phase separation in the blends. The early stages of phase separation as observed by light scattering were dominated by diffusion processes and approximately conformed to the Cahn–Hilliard linearised theory. The major effect of liquid crystal (LC) was to increase the molecular mobility of the blends. The LC generally increased the Cahn–Hilliard apparent diffusion coefficient, D app, of the blend when added with concentrations as low as 0.2 wt%. GMS and zinc stearate can also improve the mobility of the blend but to a lesser extent and the effect does not increase at higher concentration. On the other hand, the more LC added, the higher the mobility. In all systems the second derivative of the Gibbs free energy becomes zero at the same temperature. The improved mobilities therefore seem to arise from changes in dynamics rather than thermodynamic effects.

Structure and Molecular Motion of Poly(ethylene oxide) Chains Tethered on Silica by Solid-State 13C NMR Method

Solid-state 13C cross-polarization/magic-angle spinning/dipolar Decoupling (CP/MAS/DD) nuclear magnetic resonance (NMR) spectroscopy of poly(ethylene oxide) (PEO) tethered on silica was studied to characterize the conformation and dynamics of PEO chains. Temperature dependent NMR spectra could be interpreted in terms of the degree of interaction between PEO and silica molecules. The structures and molecular motion of the chains are strongly dependent on the grafting ratio (GR). Chemical shift of the methylene peak of the 13C NMR spectrum increases with GR. 70.2 ppm in low GR indicates “train” segments strongly interacted with the silica surface, whereas of 71.2 ppm in high GR is originated from “tail” (“loop”) segments separated from the surface. The fractional amount of “train” segment decreases remarkably with increase in GR. From the temperature dependence of the line width of the NMR spectra, correlation time, activation energy and transition temperature of the molecular motion were estimated. Molecular mobility of the “tail” segment was much higher and that of the “train” segment was lower than PEO chains in the amorphous region of the homopolymer bulk. “Tail” segments may thus protrude from the silica surface and have low segmental density, whereas “train” segments are trapped near the silica surface. It can be also considered that the fractional amount of “tail” segment increases abruptly with grafting ratio after the tethered chains of a coiled structure form one monolayer.

One- and Two-Dimensional MAS 13C NMR Analyses of Molecular Motions in Poly(2-hydroxypropyl Ether of Bisphenol-A)

The dynamics of amorphous poly(2-hydroxypropyl ether of bisphenol-A) (PHR), quenched from the melt, has been investigated by one- and two-dimensional solid-state 13C NMR spectroscopy. CP/MAS and dipolar decoupled/MAS 13C NMR spectra from −150 to 180 °C give two specific features: (1) below 23 °C, resonance lines for C−H carbons of phenylene rings split into two lines; (2) line widths of resonance lines become broad at 110−140 °C (30−60 °C above the glass transition temperature). Feature 1 indicates that phenylene C−H carbons exist in two magnetically different sites at low temperatures. These two sites are associated with asymmetric conformational states, which may be produced by OH···π hydrogen bond formation. The coalescence of the resonance lines at elevated temperatures is caused by the π flip motion of phenylene rings, which corresponds to the γ relaxation for PHR. The correlation time of the π flip motion is analyzed by the two-site exchange model and is found to follow the Arrhenius equation. The apparent activation energy is 51 kJ mol-1 by assuming an inhomogeneous correlation time distribution described by a Kohlrausch−Williams−Watts (KWW) function with an exponent of 0.2. Feature 2 is caused by the so-called motional broadening, which is originated by enhanced segmental motions. This dynamics corresponds to the α relaxation for PHR and can be described by the William−Landel−Ferry (WLF) equation. Two-dimensional (2D) CP/MAS 13C exchange NMR experiments confirm the existence of flip angle distribution as well as the distribution of correlation times of the phenylene ring π flip motion. The 2D experiments at −120 °C confirm the KWW exponent of 0.2.

Structure and Molecular Motion of Poly(ethylene oxide) Chains Tethered on Silica, Depended on Grafting Ratio by the Spin Labeled Method

Electron spin resonance (ESR) spectroscopy of spin-labeled poly(ethylene oxide) (SL-PEO) tethered on silica was studied to characterize the conformation and local dynamics of the chain end. The e.s.r. spectra could be interpreted in terms of two components from two different kinds of spin labels attached to “train” and “tail” segments, which were strongly and weakly interacted with the silica surface. The structure and molecular motion of the chains are strongly dependent on the grafting ratio. The fractional amount of the “train” segment decreases remarkably with an increase in the grafting ratio. From the temperature dependence of the e.s.r. spectra, it was found that the molecular mobility of the “tail” segment was higher and that of the “train” segment was extremely lower than the PEO chains in the homopolymer bulk. These facts suggest that the “tail” segments are protruding from the silica surface and having a low segmental density, whereas the “train” segments are trapped near the silica surface. It can be also considered that the fractional amount of the “tail” segment increases abruptly with an increase in the grafting ratio after the tethered chains of a coiled structure form one monolayer.

Structure and electrical transport property of poly(3-octylthiophene)

The relationship between electrical transport property and microscopic molecular motion in poly(3-octylthiophene) (POT) was investigated. We observed the temperature gradient of thermoelectric power S(T) changes at around 220K and 250K in POTs doped with ClO4− or FeCl4−. NMR results show that the observed anomaly in S(T) is closely related to the molecular motion of side chain, which might affect the scattering process of conduction electrons.

Dielectric Relaxation Studies on Molecular Motion of Poly(fluoroalkyl α-substituted acrylate)s and Compass Motion Model for Internal Motion of the Fluoroalkyl Side Chain

Dielectric measurements were made on poly(fluoroalkyl α-substituted acrylate)s, −[−CH2CX(COO(CH2)m(CF2)nY)−]p− [PX−Hm−Fn−Y, X = α-substituent (F, Cl, Me, H), Y = F or H], over a wide temperature ra...

Molecular motion of poly(methyl methacrylate) chains tethered on a polyethylene surface by the spin-label method

Methyl methacrylate monomer was graft-copolymerized on a polyethylene (PE) surface and the tethered poly(methyl methacrylate) (PMMA) chains were spin-labelled to study the molecular motion of the PMMA chains by electron spin resonance (e.s.r.). Molecular mobility of the PMMA chains is strongly affected by physical structures of both PE and PMMA phases. For example, the transition temperature of molecular motion, T 5.0 mT , at which the extreme separation width due to 14N anisotropic hyperfine splitting is 5.0 mT, increases with increases in the grafting ratio and the crystallinity of the PE phase. The transition temperature for the grafted sample is lower than that for PMMA homopolymer bulk and the mobility of the PMMA chains in the mobile region of the grafted sample is much higher than that of PE chains on the PE surface. It is concluded that the structure and molecular motion of the PMMA chains tethered on the PE surface are strongly affected by the PE chains in the amorphous phase, the structure and molecular motion of which are also closely related to the crystallinity and/or the size of crystalline PE.

Morphology and Molecular Motion of Poly(ethylene terephthalate) in Polymer/Oligomer Gel

The structural heterogeneity and molecular motion in a thermoreversible gel consisting of poly(ethylene terephthalate) (PET) and a liquid ethylene glycol oligomer (PEG) was investigated by solid-state NMR and FT−Raman spectroscopies. PET was dissolved in PEG at elevated temperatures to form a concentrated solution (30 wt %), and the solution formed a gel rapidly on cooling. For the purpose of comparison, a PET/phenol binary system and PET crystallized by annealing methods were also investigated. The longest solid-state NMR relaxation times of 13C (13CT1) in PET of PET/PEG gel among the samples indicated the slowest molecular motion and the highest rigidity PET chains. The structural heterogeneity of the PET/PEG gel investigated by HT1 measurement and confirmed by FT−Raman spectroscopy indicated phase transition during gelation. The crystallinity of PET recovered from polymer/oligomer gels is near 70% as measured by wide-angle X-ray diffraction, which is about 20% higher than that for PET samples crystalli...

Structure and molecular motion of poly(ethylene oxide) chains adsorbed on a silica-tethered poly(methyl methacrylate) by the spin label method

The spin-label method was used to study the structure and molecular motion of poly(ethylene oxide) (PEO) chains adsorbed on a silica-tethered poly(methyl methacrylate) (PMMA). Spin-labelled PEO with a narrow molecular weight distribution, having number averaged molecular weight (MN)=6.0×103, was adsorbed on the surface of the silica-tethered PMMA with various grafting ratios in carbon tetrachloride solution at 35 °C. ESR spectra were measured at various temperatures after the samples were completely dried.

Crowned polyacetylene. 4.

Chain conformations and molecular motions of poly(4'-ethynylbenzo-15-crown-5) (PEB15C5) and its annealed sample (AN-PEB15C5) in the solid state were investigated by 1 H NMR and CP-MAS 13 C NMR measurements. The chain conformation was determined to be cis-transoidal for PEB15C5 and 70°-deflected trans-transoidal for AN-PEB15C5. The exothermic peak at 180 °C observed in the DSC thermogram was due to the cis-trans isomerization. Motional modes of each chain were observed in the three temperature regions of γ, β and α with an increase of temperature, which are attributed to the sterically hindered oscillation of the side chains and the vibrational and free rotations of the main chain with the oscillating side chain. The free rotation of the trans chain in the α-region occured in a lower temperature region by 15 °C, comparing with that of cis chain.

Structure and molecular motion of poly(ethylene oxide) chains tethered on silica by the spin label method: effect of polystyrene adsorption

Electron spin resonance (e.s.r.) spectroscopy of spin-labelled poly(ethylene oxide) (SL-PEO) tethered on silica was studied to characterize the conformation and local dynamics of the chain end. Non-labelled polystyrene (PS) with narrow molecular weight distributions, having weight-average molecular weights ( M w ) of 9.64 × 10 4 (PS-96) and 3.84 × 10 5 (PS-384), were adsorbed on the surface of the silica-tethered PEO with 1.9% grafting ratio in carbon tetrachloride solution at 35°C. E.s.r. spectra of the tethered SL-PEO were observed at various temperatures after the samples were completely dried. The structure and molecular motion of the PEO chains are strongly dependent on the M w of PS. From the temperature dependence, it was found that the molecular mobility of the tethered PEO chains increased when the large PS-384 molecules were adsorbed on the surface. The chain ends of the PEO chains were mobile even at − 196°C. These facts suggest that the PS chains spread out the PEO chains and are adsorbed on the silica surface as ‘train’ segments, whereas the PEO chains protrude from the surface as ‘tail’ segments. On the other hand, when the small PS-96 molecules are adsorbed, the rate of motion of the tethered PEO chains is slowed down by the PS chains. This suggests that the PS chains are distant from the silica surface and entangled with the PEO chains.

One- and Two-Dimensional Solid-State 13C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

The crystalline−noncrystalline structure and molecular motion of poly(ε-caprolactone) (PCL) isothermally crystallized from the melt have been investigated by one- and two-dimensional solid-state 13C NMR spectroscopy. The 13C spin−lattice relaxation time (T1C) analysis reveals that the PCL sample contains three components with different T1C values, which are assignable to the crystalline, mobile crystalline, and noncrystalline components. By the 13C spin−spin relaxation time (T2C) analysis, it is found that the noncrystalline component can be further resolved into the crystalline−amorphous interfacial, and amorphous components. The mass fractions of the crystalline, interfacial, and amorphous components are finally determined to be 0.42, 0.30, and 0.28, respectively. In the crystalline region, different molecular mobilities along the methylene sequence are suggested through the difference in T1C value for the constituting carbons. More detailed molecular motion in the crystalline region has been characterized by the analysis of the 13C chemical shift anisotropy (CSA) in terms of the two-site exchange model. 13C CSA spectra of the individual carbons are successfully recorded by using the two-dimensional switching angle sample spinning technique. The CSA spectrum of the carbonyl carbon exhibit that the carbonyl carbon is almost in the rigid state or undergoes the jump motion around the molecular chain axis with a jump angle less than 30°. In contrast, methylene carbons exhibit almost axially symmetric CSA spectra, suggesting the rapid jump motions around the molecular chain axis with a jump angle of 60−90°. Further narrowed CSA spectra, which are still axially symmetric, are observed for the methylene carbons not directly attached to the ester group, suggesting the existence of additional enhanced jump motion around the C−C bonds. Such enhanced molecular motions of the methylene sequence may be due to the distorted nonplanar zigzag chain conformation of PCL in the crystalline region.

Comments on the Structural Heterogeneity and Molecular Motion in Poly(vinyl chloride) (PVC) and Poly(ether−ester) Characterized by Solid State NMR

Comments on the Structural Heterogeneity and Molecular Motion in Poly(vinyl chloride) (PVC) and Poly(ether−ester) Characterized by Solid State NMR

Anomalous Diffusion in an Aqueous System of a Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Triblock Copolymer during Gelation Studied by Pulsed Field Gradient NMR

The molecular motion of poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) block copolymer in water was investigated during the temperature-induced sol−gel transition with the aid of pulsed field gradient NMR. The strong slowing down of the diffusive motion in the gel regime is accompanied by an increased nonexponentiality of the spin echo attenuation function. The value of the stretched exponent, describing the decay of the spin echo attenuation, decreases with increasing temperature, and this trend suggests a broader distribution of diffusion coefficients when approaching the gel state. Ordinary diffusion behavior is observed in the sol phase, whereas anomalous diffusion is detected as the gel evolves, and the mean square displacement 〈z2〉 shows a power law dependence on time (〈z2〉 ∝ tα) with α < 1. The value of α decreases as the gelation process proceeds, and α is around 0.5 in the gel zone, but a wave vector dependence of α can be traced at temperatures in the gel regime.

Effects of Aging on Molecular Motion of Poly(1-trimethylsilyl-1-propyne) Membranes Synthesized Using Vanous Catalysts

Effects of Aging on Molecular Motion of Poly(1-trimethylsilyl-1-propyne) Membranes Synthesized Using Vanous Catalysts

Miscibility and Molecular Motion of Poly(methyl acrylate)/Poly(vinyl acetate) Blend as Studied by 13C NMR in the Solid State

Miscibility and molecular motion of a poly(methyl acrylate)/poly(vinyl acetate) blend are studied by high-resolution solid-state 13C NMR techniques. Observed 1H relaxation times indicate that they are miscible on the scale of 20—30 A. The temperature dependence of the 13C linewidth is examined to investigate effects of blending on molecular motion of each component polymer. Two models for the temperature dependence of the correlation time of motion are examined. One is an Arrhenius dependence and the other is a WLF dependence. Both models explain the observed temperature dependence adequately. It is shown that by blending molecular motions of PMA and PVAc becomes similar.