High resolution 1H-NMR relaxation study of polyisobutylene in solution

From the temperature dependence of integrated intensities and from line widths in high-resolution ¹H-NMR spectra, the relaxation times T₁ and T₂ of protons in CH₂ and CH₃ groups of polyisobutylene in CCl₄ solution have been determined. Although the relaxation time T₁ of methylene protons is determined mainly by intragroup interactions, intergroup interactions of two methyl groups from each two consecutive monomer units were found to contribute considerably to T₁ of methyl protons. The Structure and mobility of polyisobutylene (PIB) molecules in solution is discussed on the basis of the relaxation time data.     

Carbon-13 NMR spin-lattice relaxation times of isotactic and syndiotactic sequences in amorphous polypropylene

Spin-lattice relaxation times (T₁) for methyl, methylene, and methine carbons in an amorphous polypropylene have been measured as a function of temperature from 46 to 138°C. The carbons from isotactic sequences characteristically exhibited the longest T₁'s of those observed. The T₁ differences increased with temperature with the largest difference occuring for methine carbons where a 32% difference was observed. Activation energies were determined for the motional processes affecting T₁'s for isotactic and syndiotactic sequences with essentially no dependence upon configuration noted.     

The structural dependence of vicinal 13C?13C coupling constants in s-cis-butane and cis-butane

The dependence of three-bond ¹³C-¹³C couplings of cis-butane and cis-butene on the valence angle, the torsional angle of the methyl groups and methyl and methylene substituents is discussed on the basis of INDO-SCPT calculations. The results support the interpretation of the experimental couplings between the bridgehead carbons of bicyclic hydrocarbons based on a multiple-path mechanism.     

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

The 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.     

Dynamics of macromolecular chains. VI. Carbon 13 and proton nuclear magnetic relaxation of polystyrene in solution

Spin-lattice ¹H and ¹³C nuclear magnetic relaxation (NMR) times T₁ have been measured for solutions of polystyrene in hexachlorobutadiene at two different frequencies. Some nuclear Overhauser enhancements and linewidths have also been determined. At 15 and 25 MHz the relaxation times T₁ of the ortho and meta carbons show two different dependences on temperature. These measurements indicate internal motion of phenyl groups around the C_α—C_para axis. A single isotropic correlation time is inadequate to explain the relaxation data for the para carbon. Use of a diamond-lattice motional model reveals that segmental reorientation of the chain backbone of polystyrene can be described in terms of two correlation times, ρ characterizing the three-bond motion process, and θ reflecting either isotropic motions of subchains or departure from an ideal lattice. Data on low-molecular-weight polystyrene indicate the participation of overall rotatory diffusion in the relaxation process. This motion is no longer efficient in high-molecular-weight polymers, where relaxation is due to segmental reorientation.     

CARBON-13 NMR STUDY ON MOLECULAR MOTION OF 1, 2-POLYBUTADIENE——TEMPERATURE DEPENDENCE OF MOLECULAR MOTION

Proton-decoupled, ~(13)C FT-NMR (operating at 50.3 MHz) is used to determine spin-latticerelaxation time (T_1), nuclear Overhauser enhancement (NOE), linewidth and chemical shift of 1,2-polybutadiene as a function of temperature in CDCl_3 solution and the temperature dependence ofmolecular motion of 1,2-polybutadiene has been investigated with these NMR relaxation parameters.It is found that jumps of NOE and linewidth vs. temperature appear between-1℃and -30℃. Theminimum of nT_1 vs. temperature for all carbons occur at about -45℃.     

Carbon-13 spin-lattice relaxation study of linear polymers in solution

Proton-decoupled, partially relaxed, Fourier-transform NMR of ¹³C in natural abundance was used to determine spin-lattice relaxation times of individual carbons of polyisobutylene, polyacrylonitrile, poly(vinyl chloride), and poly(vinyl alcohol) in solution. It is shown that the relaxation times are independent of the difference in stereochemical configuration. From the values of the nuclear Overhauser enhancement factor it is shown that the relaxation times are independent of the difference in stereochemical configuration. From the values of the nuclear Overhauser enhancement factor it is shown that the excess spin energy from equilibration of all the ¹³C, even of quaternary carbons, in the polymers dealt with here is transferred to the lattice mainly through ¹³C-¹H dipolar interactions. It is shown that the segmental motions responsible for the spin-lattice relaxation of the polymer skeleton in solution can be described by the isotropic model within a good approximation, except for poly(vinyl alcohol) at low temperature. The activation energies of skeletal and internal methyl motions are estimated from the temperature dependence of the correlation time. Differences in the ¹³C line widths for individual carbons of polyisobutylene are discussed briefly.     

Study of molecular motions and 14N quadrupolar coupling in 1,3- and 1,4- diethylpyridinium bromides using 13C and 14N relaxation time measurements

The internal and overall motions of 1,3- and 1,4-diethylpyridinium bromides have been studied by ¹³C relaxation. The enthalpies of activation for the rotation of the ethyl groups in positions 1 and 3 are deduced from the temperature dependence of the T₁ values of the methylene and methine carbons. The ¹⁴N quadrupolar relaxation time, T_q, together with ¹³C relaxation data provide an estimate of the ¹⁴N quadrupolar coupling constants.     

Segmental motion in polyoxymethylene

The proton spin-lattice relaxation times (T₁) of melt-crystallized, solution-crystallized, and solid-state-polymerized polyoxymethylene (POM) were measured between ?60 and +150°C. The three types of samples each have a pronounced T₁ minimum near room temperature which is a high-frequency manifestation of the γ process. From the quantitative dependence of the relaxation intensity on crystallinity as well as from the absolute magnitude of the relaxation times, it is concluded that the γ process in POM arises from hindered rotation of noncrystalline chain segments. The relation between the relaxation times and the long period indicates that these noncrystalline segments constitute disordered lamellar surface layers, the thickness of which depends on thermal history of the material. The temperature dependence of the motion of the relatively thin surface layers of solution crystallized POM is quite straightforward. The γ process in the bulk-crystallized material involves cooperative motion, however, leading to temperature-dependent kinetic parameters.     

Viscoelastic properties of 1,2-polybutadiene—comparison with natural rubber and other elastomers

Viscoelastic properties of uncrosslinked 1,2-polybutadiene (91.5% vinyl, 7.0% cis, 1.5% trans, number-average molecular weight 99,000) were studied by dynamic shear measurements between 0.15 and 600 cps (torsion pendulum and Fitzgerald transducer) and shear creep measurements over time periods up to 3.7 × 10⁴ sec., in the temperature rang from 5 to 50°C. More limited dynamic measurements were made on a sample of unvulcanized natural rubber with number-average molecular weight 350,000 at frequencies from 0.4 to 400 cps and temperatures from 13 to 48°C. All data were reduced to 25°C. by shift factors calculated from equations of the WLF form with the following coefficients: 1,2-polybutadiene, c₁ = 6.23, c₂ = 72.5; natural rubber, c₁ = 5.94, c₂ = 151.6. In the transition zone, the relative positions of the loss tangent curves on the logarithmic frequency scale for these and other rubbers (1,4-polybutadiene with 50% trans configuration; styrene–butadiene rubber with 23.5% styrene content; and polyisobutylene) provided relative measures of local segment mobility. At 25°C., these ranged over a factor of 3700 with 1,2-polybutadiene and polyisobutylene the lowest and 1,4-polybutadiene the highest. When the frequency scale of each rubber was reduced to a temperature 100°C. above its glass transition temperature, however, the loss tangent curves for all except polyisobutylene were nearly coincident; the latter still showed a lower mobility by a factor of about 1/800. The terminal relaxation time and steady-state compliance for the 1,2-polybutadiene calculated from the Rouse theory were larger than those observed experimentally. The level of compliance corresponding to the entanglement network of 1,2-polybutadiene, J_eN, was calculated by integration over the loss compliance, J″, to be 1.62 × 10^?7 cm.²/dyne; integration over G″ to obtain the corresponding modulus gave reasonable agreement. From such J_eN, values, the average number of chain atoms between entanglement points, jZ_e, was estimated as follows: 1,2-polybutadiene, 132; natural rubber, 360; 1,4-polybutadiene, 110; styrene–butadiene rubber, 186; polyisobutylene, 320. Values of jZ_e were also estimated from the minimum in the loss tangent and compared with those reported from the molecular weight dependence of viscosity. The three sources were in generally good agreement.     

High-Resolution Solid-State NMR Characterization of Morphology in Annealed Polylactic Acid

Single-pulse ¹³C NMR spectra and spin-lattice relaxation times T₁(¹H), detected indirectly via ¹³C carbons, and T₁(¹³C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the ¹³C NMR lines and proton spin-lattice relaxation times T₁(¹H). The spin-lattice relaxation times T₁(¹³C) related to the respective carbons of the α-polymorph of PLA are also discussed in the study.     

Temperature dependence of molecular motions in bulk polystyrene

Time-resolved optical spectroscopy is used to investigate the reorientation of three rigid probes and one labeled chain in bulk polystyrene. Orientational correlation times for these probes and labels are found to be in the range of 10^?8–10^?10 s at temperatures of 180–300°C. Consistent with previous studies, the attachment of a chromophore into the chain backbone slows its dynamics by about an order of magnitude. The temperature dependences of the correlation times are similar to the temperature dependence of the viscosity. When combined with probe reorientation times near and below T_g, these results indicate that probe reorientation tracks the temperature dependence of the viscosity quite well over twelve decades in time. In contrast, literature results for the translational diffusion of similarly sized probes indicates a substantially weaker temperature dependence near T_g. Thus it appears that a fundamental change in the mechanism of probe motion occurs near T_g. © 1994 John Wiley & Sons, Inc.     

Dynamic study of the noncrystalline phase of 13C-labeled polyethylene by variable-temperature 13C CP/MAS NMR spectroscopy

The ¹³C spin-lattice relaxation times T₁ of ¹³C-labeled polyethylene crystallized under different conditions were measured at temperatures from ?120 to 44°C by variable-temperature solid-state high-resolution ¹³C nuclear magnetic resonance (NMR) spectroscopy, in order to determine accurately the dynamics of the noncrystalline region of the polymer. From these results, it was found that the T₁ minimum for the CH₂ carbons in the noncrystalline region of solution-crystallized polyethylene with high crystallinity appears at higher temperature by about 20°C than that of melt-quenched polyethylene with low crystallinity. This means that the molecular motion of the CH₂ carbons in the noncrystalline regions is more constrained at a given temperature in the material of higher crystallinity. Furthermore, dynamics of the noncrystalline region is discussed in terms of the ¹³C dipolar dephasing times.     

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.     

Line broadening in the 13C NMR spectra of bulk polymers above Tg

The effects of magic-angle sample spinning (MAS), high-power decoupling, and resonance frequency on the ¹³C NMR linewidths of bulk polyisobutylene and bulk trans-polybutadiene are examined. The ¹³C linewidths increase with resonance frequency, are unaffected by high-power decoupling, and are reduced to different extents by MAS. The dominant contribution of the natural linewidth of the polyisobutylene lines is confirmed. The two carbons of trans-polybutadiene have approximately equal linewidths under all conditions, a result that eliminates residual chemical shift anisotropy as a major contributor to the linewidths. The large reduction of the trans-polybutadiene linewidths with MAS, coupled with the above result, suggests that microscopic variation of magnetic susceptibility is the major factor for this semicrystalline polymer. Cross-polarized ¹³C spectra of trans-polybutadiene were obtained with and without MAS. With MAS, resonances due to the crystalline and amorphous components were resolved. The principal components of the chemical shift tensor of the vinylene carbons were obtained from the spectrum without MAS.     

Aging and degradation of polyolefins. II. γ-initiated oxidations of atactic polypropylene

Oxidations of bulk atactic polypropylene (PP) have been carried out at 22 and 45°C, and the dependence of rate of formation of each product on rate of initiation has been determined. The principal product is PP hydroperoxide, formed in a half-order reaction. One termination product is polymeric dialkyl peroxide, formed in a first-order reaction. Other termination and propagation products, alcohols and carbonyl compounds, are formed in reactions that are mostly first-order in initiation. At 22°C, G is 9–63. G is about three times as great at 45°C as at 22°C. Experiments with 2,6-di-tert-butyl-p-cresol shows that it can inhibit all non-cage propagation and all formation of PP hydroperoxide, but that it does not affect cage reactions of initiating radicals and their successors. Only about 16% of the initiating PPO₂· radicals escape the cage at 45°C. Oxidations of PP, n-hexane, and their mixture with both peroxide and γ-ray initiation show that nearly all the initiating radicals escape the cage in solution but that the concentration of PPO₂· radicals is much less than in bulk because of a much faster chain termination. Both the propagation and termination constants for PP oxidation are much faster in solution, but the changes compensate so that k_p/(2k_t)^½ is about the same in solution as in bulk.     

Photon correlation spectroscopy of syndiotactic poly (n-butyl methacrylate) near the glass transition

Slow relaxing longitudinal density fluctuations in bulk syndiotactic poly (n-butyl methacrylate) [PBMA] were studied by photon correlation spectroscopy as a function of temperature from 70 to 90°C. The shape of the light-scattering relaxation function broadened as the temperature approached the glass transition (T_g = 55°C). The average relaxation time shifted with temperature, consistent with previous studies of PBMA. The relaxation functions were analyzed in terms of a distribution of relaxation rates. The calculated distribution was clearly bimodal and the shape altered with temperature. The higher frequency peak in the distribution corresponds well with previous mechanical and dielectric relaxation studies of the intramolecular relaxation of the acrylate ester side chain. The resolution of the distribution into two modes is due to a well-defined side-chain motion with relaxation strength comparable to the primary glass-rubber relaxation. © 1994 John Wiley & Sons, Inc.     

Synthesis of polyesters as binders for deinkable inks. I. Structural analysis of the polyesterification between o-phthalic anhydride and neopentyl glycol in bulk at 200°C by high resolution 13C nuclear magnetic resonance (13C-NMR)

Analysis of the polyesterification in bulk without any external catalyst at 200°C of o-phthalic anhydride with neopentyl glycol (2,2-dimethyl-1,3-propanediol) with a mole ratio ([(SINGLE BOND) COOH]/[ (SINGLE BOND) OH]) = 0.7 has been carried out by high resolution ¹³C nuclear magnetic resonance (¹³C-NMR). Polyesters can be analyzed by ¹³C-NMR spectra because of the fact that both o-phthalic acid (o-phthalic anhydride) and neopentyl glycol carbons are sensitive to sequence effects. Spin-lattice relaxation times T₁, of quaternary, tertiary and secondary carbons in different structures are in the 0.1–6.5 s range depending on the neighboring residue effects in the polymer chain. © 1996 John Wiley & Sons, Inc.     

Nuclear magnetic resonance relaxation studies of polyacrylamide solution

 The cohesive interaction among polymer chains in a polyacrylamide (PAAm)–D₂O solution has been studied by NMR relaxation. The NMR relaxation times of PAAm in the good solvent D₂O were measured at different temperatures. The results show that the solution system has a high local viscosity and that its relaxation characteristic is soft-solid-like. The temperature dependence of the relaxation behavior of the solution is obviously different from that of ordinary polymer solutions. The difference lies in the relaxation behavior of the methylene protons in the main chain of PAAm, as shown by analyzing the relaxation process with single exponential and biexponential decays. As the temperature increases, the solvation is weakened, leading polymer chains to form curling coils, thus hindering the movement of the methylene protons among the main chains. It can be expected from the existence of 80% fast-relaxing protons that there are a zhigh number of entanglements among the polymer chains in PAAm solution. The information about entanglements among the polymer chains can be deduced from the biexponential dependence of the spin–spin relaxation on the concentration of the polymer solutions. Received: 14 April 1999/Accepted in revised form: 12 October 1999