Proton longitudinal NMR relaxation of poly(p-phenylene sulfide) in the laboratory and the rotating frames reference (original) (raw)
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Macromolecules, 1991
Results are presented for NMR measurements on a series of samples of linear polyethylene with low polydispersity over a range of molecular weights. In general terms, the experimental data are consistent with results of previous workers. The main thrust of the present investigation is to show that the transverse relaxation function can be accurately described by a recent theoretical model due to Brereton. This theory is based on a scale-invariant model of the dipolar interactions assumed responsible for the relaxation of transverse magnetization. It incorporates a rather general hierarchy of chain dynamics which can be used to accommodate the Rouse model at small space and time scales and a variety of other models, e.g., the reptation model, at larger space and time scales. The model is shown to account for the complex shape of the transverse relaxation function observed for high molecular weight samples of low polydispersity, showing that this has its origin in the restrictions on molecular mobility imposed by the entangled nature of the polymer melt.
Macromolecules, 1979
The spin-lattice relaxation times of the methyl protons of poly(2,6-dimethyl-l,4-phenylene oxide) (M,PPO) and poly(2-methyl-6-phenyl-1,4-phenylene oxide) (MPhPPO) were measured for 20% (wt/wt) solutions of each polymer in CDC1, as a function of molecular weight and temperature. The molecular weight dependence of T1 at a given temperature was interpreted with the Jones-Stockmayer specific motional model. Correlation times were obtained for three specific motions considered likely to occur in each polymer which contributes to the spin relaxation of the methyl protons. These motions are overall rotatory diffusion, three-bond crankshaft rearrangements, and anisotropic rotation of the backbone phenyl group. Methyl group rotation occurs too rapidly to effectively contribute to spin relaxation; however, it does partially average the dipoldipole interactions. At high molecular weights, relaxation in both polymers is dominated by anisotropic phenyl group rotation characterized by correlation times from 0.2 to 0.4 ns for MzPPO and from 0.2 to 0.7 ns for MPhPPO. The three-bond crankshaft rearrangements of the backbone are characterized by correlation times ranging from 2 to 13 ns for MzPPO and 2 to 21 ns for MPhPPO. The apparent activation energy for the three-bond crankshaft motion is 29 kJ/mol in M2PP0 and 32 kJ/mol in MPhPPO. The apparent activation energy for backbone phenyl group rotation is 8 kJ/mol in MzPPO and 16 kJ/mol in MPhPPO.
2000
The change in the solid-state proton NMR Free Induction Decay signal of a polyethylene sample while heating from 360 to approximately 400 K was investigated. The crystallinity, as determined by model fit, decreases approximately linearly with increasing temperature up to 393 K. At higher temperature, the crystallinity decreases faster with increasing temperature. Within the temperature region investigated, three different "phases" are identified. The change in the relative distribution of these phases versus temperature is explained quantitatively by a phase-equilibrium model. Spin-spin relaxation time measurements and second moment calculations are presented, which gives information about molecular motion within these phases. ᭧
Keywords: 1 H NMR, spin-spin relaxation, inversion of integral transformation, multiphase solid polymers. Nuclear magnetic resonance (NMR) is one of the most important analytical means of analysis of substances. Recently, NMR with compact magnets and fairly homogeneous fields has been widely used for testing of materials. Nuclear magnetic resonance relaxometry can be used for nondestructive testing of materials by means of NMR-MOUSE sensors [1]. Unlike the longitudinal relaxation time T 1 , the transverse relaxation time T 2 is a more important parameter of nuclear magnetic resonance for characterization of molecular dynamics of amorphous and semicrystalline polymers [2]. Among the most widespread methods of measuring T 2 are the methods of the Hahn echo (HE) and Carr– Purcell–Meiboom–Gill (CPMG) sequence. The Hahn echo and the CPMG sequence do not allow measuring short times Т 2 close to the dead time of the spectrometer and characteristic for vitrified or crystaqllized polymers. The problem of registering short Т 2 times can be solved using the solid-echo (SE). In [3] the destruction of some polymers upon exposure to different factors was investigated by NMR relaxometry methods, and the sensitivity of spin-spin relaxation times Т 2 to artificial polymer aging was demonstrated. The present work studies the specific features of spin-spin relaxation time distributions in a solid polymer depending on the method of registering the transverse magnetization decay and the method of finding the relaxation components. As an examined polymer sample, the outer insulation layer of radio-frequency RK-75 cable made of polyvinyl chloride (PVC) was chosen. 1 H NMR relaxation experiments at a frequency of 13.84 MHz were performed in a weak magnetic field using a Tecmag Apollo spectrometer with TNMR software. A permanent magnet with working sample region 5 mm in diameter and 20 mm long was used. The magnet consisted of two permanent magnets with sizes 60 80 100 mm connected with a U-shaped magnetic core and having a 25 mm gap. The magnetic field induction in the gap was 300 mT. The magnetic field inhomogeneity in the region where the coil with the sample was located was 0.1 mT/cm. The HE, CPMG, and SE sequences and the Ostroff–Waugh (OW) sequence [4] were used to measure the spin-spin relaxation time Т 2. The distributions of the relaxation time Т 2 were obtained by inversion of the integral transformation on the basis of the algorithm described in [5]. Decompositions in exponential and Gauss functions were performed because measurements were carried out at a temperature of 293 K lying below the vitrification temperature of polyvinylchloride. The Т 2 relaxometry is one of the methods of quantitative estimation of the phase composition of multiphase polymers. It is a complicated problem because of the complexity of multiphase composition and the complexity of molecular motion. The Т 2 relaxation signal from the rigid polymer phase is conventionally described by the Abraham or
NMR study of molecular dynamics in selected hydrophilic polymers
Solid State Nuclear Magnetic Resonance, 2004
The temperature dependencies of the 1 H spin-lattice relaxation times T 1 and of the proton NMR second moment M 2 in the temperature range from about 90 to 420 K were measured for methyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose. The proton spin-lattice relaxation measurements reveal two minima due to the C 3 reorientation of the methyl groups of the methoxy, methylenemethoxy or propylene oxide groups and the restricted motion of the segment of the polymer chain. The activation energy barriers for these motions were calculated. r
Eprint Arxiv Cond Mat 0507515, 2005
Dynamics of Yamamoto-type poly(para-phenylene)[PPP] was investigated by differential scanning calorimetry(DSC) and proton solid-state NMR relaxation spectroscopy. The DSC chart shows the baseline jump without latent heat at 295K, which is due to the glass transition of the polymer. From the variable temperature proton longitudinal relaxation time(T1) measurements, relatively short T1 is observed over the wide temperatures range from 250K (closed to Vogel-Fulcher-Tamman temperature) to 360K, inferred the existence of cooperative critical slowing down associated with the glass transition. The frequency dependence of proton longitudinal relaxation time at 295K shows R1 ∼ ω −0.5 dependence, which is due to the one-dimensional diffusion-like motion of the backbone conformational modulation. The frequency dependence is held at least up to 360K. From these experiments, we were able to observe the twist glass transition of the backbone of PPP, of which critical dynamics has a universality class of the three-dimensional XY model.
Russian Physics Journal, 2018
Nuclear magnetic resonance (NMR) is one of the most important analytical means of analysis of substances. Recently, NMR with compact magnets and fairly homogeneous fields has been widely used for testing of materials. Nuclear magnetic resonance relaxometry can be used for nondestructive testing of materials by means of NMR-MOUSE sensors [1]. Unlike the longitudinal relaxation time T 1 , the transverse relaxation time T 2 is a more important parameter of nuclear magnetic resonance for characterization of molecular dynamics of amorphous and semicrystalline polymers [2]. Among the most widespread methods of measuring T 2 are the methods of the Hahn echo (HE) and Carr-Purcell-Meiboom-Gill (CPMG) sequence. The Hahn echo and the CPMG sequence do not allow measuring short times Т 2 close to the dead time of the spectrometer and characteristic for vitrified or crystaqllized polymers. The problem of registering short Т 2 times can be solved using the solid-echo (SE). In [3] the destruction of some polymers upon exposure to different factors was investigated by NMR relaxometry methods, and the sensitivity of spin-spin relaxation times Т 2 to artificial polymer aging was demonstrated. The present work studies the specific features of spin-spin relaxation time distributions in a solid polymer depending on the method of registering the transverse magnetization decay and the method of finding the relaxation components. As an examined polymer sample, the outer insulation layer of radio-frequency RK-75 cable made of polyvinyl chloride (PVC) was chosen. 1 H NMR relaxation experiments at a frequency of 13.84 MHz were performed in a weak magnetic field using a Tecmag Apollo spectrometer with TNMR software. A permanent magnet with working sample region 5 mm in diameter and 20 mm long was used. The magnet consisted of two permanent magnets with sizes 60 80 100 mm connected with a U-shaped magnetic core and having a 25 mm gap. The magnetic field induction in the gap was 300 mT. The magnetic field inhomogeneity in the region where the coil with the sample was located was 0.1 mT/cm. The HE, CPMG, and SE sequences and the Ostroff-Waugh (OW) sequence [4] were used to measure the spin-spin relaxation time Т 2. The distributions of the relaxation time Т 2 were obtained by inversion of the integral transformation on the basis of the algorithm described in [5]. Decompositions in exponential and Gauss functions were performed because measurements were carried out at a temperature of 293 K lying below the vitrification temperature of polyvinylchloride. The Т 2 relaxometry is one of the methods of quantitative estimation of the phase composition of multiphase polymers. It is a complicated problem because of the complexity of multiphase composition and the complexity of molecular motion. The Т 2 relaxation signal from the rigid polymer phase is conventionally described by the Abraham or
NMR molecular dynamic study of high crystalline polymers
Polymer Testing, 2000
Analysis of the dynamic behaviour of two highly crystalline polymers, polyethylene (HDPE) and polypropylene (iPP) was carried out by solution and solid state nuclear magnetic resonance (NMR) to obtain the response of the behaviour of both polymers with respect to the molecular chain dynamics, the chain ordination and the molecular packing. The proton spin-lattice relaxation time in the rotating frame (T 1 H ρ) showed that HDPE is more rigid than iPP, because the chain orientation and the molecular packing are different. T 1 H ρ parameter also depends on the molecular chain dynamics, as a result of the different sequence distribution in the domains