Solid‐State NMR Study on Relationships between Miscibility and Chain Mobility in Poly(4‐Methylstyrene)/Poly(Cyclohexyl Methacrylate) Blend

The phase behavior and motional mobility in binary blends of poly(4‐methylstyrene) (P4MS) and poly(cyclohexyl methacrylate) (PCHMA) have been examined by ¹³C solid state NMR techniques. The blend miscibility was studied by measuring the ¹H spin‐relaxation times in the laboratory frame (T₁^H) and in the rotating frame (T_1ρ^H), respectively. Although intermolecular spin diffusion contributes to the proton relaxations in accordance with homogeneity, T_1ρ^H data shows signs of in complete averaging. The T_1ρ^H relaxation behavior indicates the existence of heterogeneous do mains with shortest dimensions in the nanometer range, which is also sup ported by the intermolecular cross polarization experiments with variable contact times. In addition, according to the resuits of carbon T_1ρ relaxation time measurements, it is concluded that mixing is intimate some what enough to cause a reduction in local chain mobility for P4MS and vice versa for PCHMA.     

Specific Features of the Adsorption and Nuclear Magnetic Relaxation of the Water Molecules in Active Carbons: 2. The State of Water in Active Carbon with Relatively Large Pores According to the NMR Relaxation Data

The state of water upon adsorption on FAS-3 active carbon with relatively large micropores is studied by the NMR relaxation method. The dependences of the times of spin–lattice (T ₁) and spin–spin (T ₂) NMR relaxation of adsorbed water molecules on the adsorption value are established. The character of the dependences of T ₁ and T ₂ on the number of adsorbed water molecules per primary adsorption site reflects the specific features of the volume filling of micropores and the formation of a continuous adsorption layer on the mesopore surface due to cluster coalescence on the one wall of a pore. The results obtained are compared with the data for typical microporous active carbons, as well as with the data obtained by the adsorption method.     

Variable temperature 19F solid‐state NMR study of the effect of electrostatic interactions on thermally‐stimulated molecular motions in perfluorosulfonate ionomers

This study uses variable temperature ¹⁹F solid‐state nuclear magnetic resonance (SSNMR) spectroscopy to determine the influence of electrostatic interactions on the T₁, T_1ρ, and T₂ values of Nafion®. Because of a “homogenizing” of the T₁'s as a result of spin diffusion, it was not possible to resolve from the T₁ experiments the relative motions of the side‐ and main‐chain. The initial increase in T_1ρ as a function of increasing temperature has been attributed to backbone rotations that increase with increasing temperature. The maxima observed in the T_1ρ plots suggest a change in the dominant relaxation mechanism at that temperature. The similarity in relaxation behavior of the side‐ and main‐chains suggests that the motions are dynamically coupled, because of the fact that the side‐chain is directly attached to the main‐chain. Two T_1ρ values were observed for the main‐chain at high temperatures, which has been attributed to a thermally activated ion‐hopping process. The results of T₂ studies show that correlated motions of the side‐ and main‐chain exist at low temperatures. However, at elevated temperatures the T₂ values for the side‐chain increase rapidly while remaining relatively constant for the main‐chain, indicating an onset of mobility of the side‐chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2177–2186, 2007     

Solid-state 13C-NMR studies of the aging of poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Solid state ¹³C-NMR was used to investigate the miscibility and subsequent separation of solution-cast blends of poly(vinylidene fluoride) (PVF₂) and poly(methyl methacrylate) (PMMA) with aging for a range of compositions. It was found that one amorphous phase and intimate mixing of the polymer chains in this phase existed for all compositions of the blends, even after 2 months of aging at room temperature as determined by the proton spin lattice relaxation time T_1ρH in the rotating frame, and the time constant T_CH for transfer of magnetization. The T_1ρH is sensitive to the spatial homogeneity of the blend via spin diffusion and would indicate the presence of phases or domains in the amorphous component of the blend larger than approximately 19 Å. The T_CH is proportional to the inverse sixth power of the interatomic distances needed for transfer of magnetization from proton to carbon and would be sensitive to a separation of polymer chains in the amorphous phase with aging on the order of 4–5 Å. There was an increase of the T_1ρH and T_CH values with aging, indicating that a subtle separation between unlike chains in the amorphous phase was occurring although a single amorphous phase was present.     

Studies of micro-brownian motion of a polymer chain by the fluorescence polarization method. I. Fluorescent conjugates of polyacrylamide

Polyacrylamide having a fluorescent residue at the chain end was prepared by polymerization of acrylamide in the presence of a fluorescent dye. The segmental motion of the chain end in dilute solution was studied by the fluorescence polarization method on the fluorescent polyacrylamide conjugates thus obtained. The linear relation between 1/p and T/η₀ held for every sample studied in aqueous media, where p is the degree of polarization of the fluorescence, T is the absolute temperature, and η₀ is the viscosity of the medium. The mean relaxation time 〈ρ〉 of the conjugate was evaluated from these data as a function of the molecular weight of the conjugate. The value of 〈ρ〉 increased slightly with molecular weight, varying from 3.3 × 10^?9 to 7 × 10^?9 sec. The absolute values of 〈ρ〉 and its molecular weight dependence suggest that 〈ρ〉 represents the mean rotational relaxation time for the cooperative motion of about ten monomeric units at the chain end. The effect of the mean extension of polymer chain on the segmental motion was found to be negligible.     

Rotating frame proton spin-lattice relaxation measurements of poly (ethylene oxides)

Measurements of T_lρ as a function of temperature have been made on two polyethylene oxides (PEO) with molecular masses of 5,000 and 30,000. The T_1ρ measurements show biexponential behavior of the relaxation function in the temperature range from 170 K to 350 K. The intensities of the components of the relaxation function are constant over this temperature range in agreement with the crystallinities of the samples. The two relaxation times can be associated with the crystalline and amorphous component; the relaxation time minima describe the α relaxation in the crystalline regions of PEO and the glass transition in amorphous PEO.     

Physical properties of the nonlinear optical material Li2B4O7 studied by static NMR and MAS NMR

The mechanisms behind the nonlinear optical (NLO) properties of Li₂B₄O₇ are characterized by ⁷Li static nuclear magnetic resonance (NMR) and magic-angle spinning (MAS) NMR. Furthermore, the structural nature of 3-coordinate BO₃ and 4-coordinate BO₄ groups is also characterized by the same method. For ⁷Li and ¹¹B, the spin-lattice relaxation time T₁ in laboratory frame gradually decreases with increasing temperature, whereas the spin-lattice relaxation time T_1ρ in rotating frame, which differs from T₁, is nearly constant. In addition, the activation energies of ⁷Li and ¹¹B, which are obtained via the values of T₁ and T_1ρ, are also compared.     

Solid state 15N NMR study of 15N enriched melamine-formaldehyde resins

Molecular dynamics and structure of uncured and cured melamine-formaldehyde resins isotopically ¹⁵N enriched at amine sites were studied by solid-state ¹⁵N nuclear magnetic resonance (NMR). Spectra recorded with direct (DP) and cross-polarization (CP) pulse sequences reflect two motionally different regions arising from similar chemical structures. DP spectra of uncured resins at higher temperatures have narrow lines and the detection of slightly different structural units is possible. With increasing crosslinking resonances broaden and overlap and the direct detection of individual signals in cured resins is not possible. On the basis of variable contact time, variable spinning speed, and interrupted decoupling experiments three protonated and one nonprotonated group of signals are identified in the CP spectra for all samples. Short polarization-transfer rates, T_NH, for nonprotonated nitrogen in uncured and lightly cured samples reveal more effective hydrogen bonding in viscous and rubber-like resins compared to the highly cured rigid resins. The rigid portions of the resins exhibit longer T₁ and short T_1ρ relaxation times, while the shorter T₁ times and longer T_1ρ times are associated with the more mobile portion of samples. ©1995 John Wiley & Sons, Inc.     

High-resolution solid-state 13C NMR study of ethylcellulose films

Ethylcellulose films cast from concentrated solutions of chloroform, benzene, and carbon tetrachloride were subjected to the NMR relaxation measurements including ¹H spin-lattice relaxation time (T_1H), rotating-frame ¹H spin-lattice relaxation time (T_1ρH), and ¹³C spin-lattice relaxation time (T_1C). The values of T_1ρH for carbons in the glucose units of ethyl-cellulose were of the same order of magnitude as those reported for the crystalline and noncrystalline regions of ramie cellulose. The values of T_1C for unsubstituted C2, C3 carbons were smaller than those for the corresponding carbons in the noncrystalline region of native celluloses. The T_1C values for unsubstituted C2, C3, and substituted C6 carbons showed a small but definite dependence on the solvent from which the films were cast. © 1993 John Wiley & Sons, Inc.     

An NMR study of the electron beam-induced polymerization of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate

Electron beam-induced polymerization of trimethylolpropane triacrylate (TMPTA) and its methacrylate analog (TMPTMA) was studied using nuclear magnetic resonance (NMR) relaxation time measurements. Free induction decays (FID) of partially polymerized samples consist of a short Gaussian component and a longer component comprised of a distribution of simple exponentials. The relative intensity of the Gaussian component increases with radiation dose. T₁ and T_1ρ values were measured as a function of temperature and radiation dose. The relaxation is due primarily to methyl group reorientation at low temperatures, ethyl group reorientation at intermediate temperatures, and whole-molecule reorientation at high temperatures. In both compounds, the T₁ and T_1ρ values at the high temperature minima increase with increasing dose, and the minima values can be used to estimate the degree of polymerization. The temperature at which the T_1ρ minimum occurs increases with dose, suggesting an increase in the glass transition temperature, T_g, with polymerization. The polymerization appears to have very little effect on the low temperature CH₃ reorientation in TMPTA. In TMPTMA the polymerization appears to reduce the mobility of the methacrylate methyl groups.     

A model for dynamic relaxations in amorphous polymers. II. Extensions and generalizations of formalism and application to poly(methacrylates)

Extensions and generalizations of a new model for the dynamic relaxations in amorphous polymers, and its application to the poly(methacrylates), will be presented. The sizes of moving subunits will be extrapolated for the β and γ relaxations in several poly(methacrylates), by working backward from the relaxation temperatures (T_r) observed at frequencies of 1 to 100 Hz to subunits giving T_cs comparable to those T_rs. A general form will be proposed for activation energy distributions; and used to derive relaxation time distributions satisfying the experimental trends. The good agreement between the calculated T_c and the T_r observed dynamically at frequencies of 1 to 100 Hz will be shown to result from the nature of these distributions. The loss peak observed at very low temperatures by isochronal sweeps at very low frequencies is therefore caused by the dissipation of applied energy in localized domains. At sweep frequencies of 1 to 100 Hz, T_r ≈ T_c, and energy dissipation begins to take place over regions spanning the entire polymer. This delocalization of the energy dissipation is relevant to the effects of molecular level factors on many mechanical and thermodynamic properties of amorphous polymers. The effects of activation entropy and of dynamic excess entropy will be shown to be small in magnitude but important in terms of fully understanding relaxation behavior. Physical aging will be shown to result in a slight increase in the calculated characteristic temperatures. Finally, it will be shown that the relaxation behavior of the moduli and the compliances share some important common features with many other physical phenomena of seemingly very different nature.     

New (p, ρ, T) data for carbon dioxide – Nitrogen mixtures from (250 to 400) K at pressures up to 20 MPa

Comprehensive (p, ρ, T) measurements on two binary mixtures (0.10 CO₂ + 0.90 N₂ and 0.15 CO₂ + 0.85 N₂) were carried out in the gas phase at seven isotherms between (250 and 400) K and pressures up to 20 MPa using a single sinker densimeter with magnetic suspension coupling. A total of 69 (p, ρ, T) data for the first mixture and 69 (p, ρ, T) data for the second are presented in this article. The uncertainty in density was estimated to be (0.02 to 0.15)%, while the uncertainty in temperature was 3.9 mK and the uncertainty in pressure was less than 0.015% (coverage factor k = 2). Experimental results were compared with densities calculated from the GERG equation of state and with data reported by other authors for similar mixtures. Results yielded that, while deviations between experimental data and values calculated from the GERG equation were lower than 0.05% in density for low pressures, the relative error at high pressures and low temperatures increased to about (0.2 to 0.3)%. The main aim of this work was to contribute to an accurate density data base for CO₂/N₂ mixtures and to check or improve equations of state existing for these binary mixtures.     

On the theory of the effective nuclear magnetic relaxation time T2e and its application to polymer melts

A general expression for the magnetization decay of a multipulse group is derived. This formula is applied to a three-component model of molecular motions in polymer melts. The influence of the several components on the magnetization decay is discussed. The relation of the effective nuclear magnetic relaxation time T_2e to the Anderson-Weiss formula is also shown, and an analytical expression for the transverse relaxation in melts is derived. Finally T_2e is compared with the relaxation time in the rotating frame T_1ρ in the melt. The theoretical results for T_2e are tested with measurements of frequency dependence in polyethylene melts.     

The Role of Titanium Dioxide on the Hydration of Portland Cement: A Combined NMR and Ultrasonic Study

Titanium dioxide (TiO₂) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO₂ influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO₂ were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO₂ enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T₁ results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T₁ values and large capillary pores with long T₁ values. During early hydration times, TiO₂ is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO₂ appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results.     

Nuclear relaxation in atactic polystyrenes: T1 and T1ρ measurements

Measurements have been made on a series of linear atactic polystyrenes whose molecular weights range from 900 to 1.8 × 10⁶, where M _w/M _n ? 1.2. Spin lattice relaxation times have been measured in the laboratory frame (T₁) and in the rotating frame (T_1ρ) in the temperature range 90–500°K. Two major relaxation minima were observed in both sets of measurements. The high temperature process corresponds to the glass transition (α process), the position of the minimum depending on the chain length. The low temperature process appears to originate from the n-butyl endgroups in the polymer, its position being independent of chain length while its intensity is inversely proportional to molecular weight. No other minima were observed, in contrast to some other observations made by broadline and pulsed NMR techniques. Relaxation was exponential in all cases except in the region of the high temperature T_1ρ minimum and above. This nonexponential behavior is possibly connected with the transition at T > T_g observed by a number of other techniques and which is thought to correspond to a transition between two types of liquid state. A correlation frequency diagram has been drawn for all the processes observed in polystyrene by other techniques, (α, β, αβ, γ, and δ) which shows that the T₁ and T_1ρ minimum positions correlate well with the α process and that there is a possible contribution to the relaxation due to the γ process on the low temperature side of the α process. At these measurement frequencies the α and β processes are merged into an αβ process. There is no evidence for a contribution from the mechanical δ process. The effect of the endgroups is observed to very high molecular weights (4.98 × 10⁵), and it seems that a three-dimensional diffusion model would be more adequate than the one-dimensional model used to interpret similar behavior of paraffins and polyethylenes. Measurements of T₁ in the low-temperature region would constitute a method for a rough measurement of the molecular weight of these polymers.     

Quantitative nuclear magnetic resonance imaging of liquids in swelling polymers

The variation of nuclear magnetic resonance (NMR) relaxation parameters (T₁, T₂) within a polymer during swelling, limits the absolute accuracy with which liquid concentration profiles can be obtained using NMR imaging. In this article a study of the diffusion of decalin into ultra-high molecular weight polyethylene (UHMWPE) is reported. The study illustrates the use of a method of analysis whereby quantitative solvent profiles can be obtained from data influenced by both T₁ and T₂ contrast effects. A T₁ and T₂ map are obtained at a point in the uptake of liquid where the greatest range in liquid concentration is obtained at a point in the uptake of liquid where the greatest range in liquid concentration is observed. The intensity of signal corresponding to liquid in the polymer is compared to that of pure liquid in a reference sample, and correlations for T₁ and T₂ values versus signal intensity are used to deconvolve relaxation contrast, to yield the true liquid concentration. The technique was used to study the effect of degree of crosslinking of UHMWPE on the swelling kinetics and decalin transport within the polymer. A spin-echo imaging technique was used with a recycle delay approximately equal to the average spin-lattice relaxation time of the liquid, and an echo time approximately half the average spin-spin relaxation time. Under these conditions the relaxation contrast was significant, yet the mass uptake data derived from the concentration profiles obtained, using the method of analysis described, agreed well with gravimetric data. © 1995 John Wiley & Sons, Inc.     

High Melting Point of Linear,Spiral Polyethylene Nanofibers and Polyethylene Microspheres Obtained Through Confined Polymerization by a PPM-Supported Ziegler-Natta Catalyst

In this work, different types of polyethylene (linear, spiral nanofibers and microspheres) were obtained via confined polymerization by a PPM-supported Ziegler-Natta catalyst. Firstly, the Ziegler-Natta catalyst was chemical bonded inside the porous polymer microspheres (PPMs) supports with different pore diameter and supports size through chemical reaction. Then slightly and highly confined polymerization occurred in the PPM-supported Ziegler-Natta catalysts. SEM results illustrated that the slightly confined polymerization was easy to obtain linear and spiral nanofibers, and the nanofibers were observed in polyethylene catalyzed by PPMs-1#/cat and PPMs-2#/cat with low pore diameter (about 23 nm). Furthermore, the highly confined polymerization produced polyethylene microspheres, which obtained through other PPM-supported Ziegler-Natta catalysts with high pore diameter. In addition, high second melting point (T_m2: up to 143.3 °C) is a unique property of the polyethylene obtained by the PPM-supported Ziegler-Natta catalyst after removing the residue through physical treatment. The high T_m2 was ascribed to low surface free energy (σ_e), which was owing to the entanglement of polyethylene polymerized in the PPMs supports with interconnected multi-modal pore structure.     

Spin-lattice relaxations study of water mobility in natural natrolite

The mobility of water molecules in natural natrolite (Na₂Al₂Si₃O₁₀?2H₂O) is investigated by the ¹H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames (T₁ and T_1ρ) are measured as a function of the temperature for a polycrystalline sample. From experimental T₁ data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T_1ρ data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature (T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe³⁺ ions) becomes significant as a relaxation mechanism of ¹H nuclei.     

Interactions and mobility of copper(II)-imidazole-containing copolymers

Poly(1-vinylimidazole-co-methyl methacrylate) copolymers (PVM) were obtained from copolymerization of 1-vinylimidazole and methyl methacrylate with 2,2^′-azobisisobutyronitrile as an initiator. The formation of random copolymers was substantiated by the glass transition temperature (T_g) and the proton spin-lattice relaxation time in the rotating frame (T^H_1ρ). Cu(II)-PVM complexes were prepared by mixing tetrahydrofuran solution of PVM and copper sulfate solution. The formation of coordination bond between PVM and Cu²⁺ ions was studied using differential scanning calorimetry, infrared and ¹³C solid-stated nuclear magnetic resonance spectroscopy. A single composition dependent T_g was obtained for the PVM copolymers, and that increased with increasing VI content. The T_g value of the Cu(II)-PVM complex was much higher than that of the PVM copolymer with the same composition. The T^H_1ρ of the VI units and MMA units in the copolymers and complexes had one value, and that in the complexes was much lower than that in the copolymers. The dramatic decrease in T^H_1ρ for the Cu(II)-PVM complexes was due to Cu(II) complexation and electron-nuclear dipolar interactions.