NMR relaxation study of crosslinked cis-1,4-polybutadiene

Proton relaxation measurements have been used to investigate the effects of crosslinking on the segmental motion in cis-1,4-polybutadiene samples. The temperature dependence of proton spin–lattice relaxation time T₁ and spin–spin relaxation time T₂ at 60 and 24.3 MHz are reported in cis-1,4-polybutadiene (PB) samples with different crosslink density including uncrosslinked PB and samples with 140, 40, and 14 repeat units between crosslinks. In addition, spin-lattice relaxation times in rotating coordinate frame, T_1p, have also been determined. The relaxation data are interpreted in terms of the effects of crosslinks on segmental chain motions. Because of their sensitivity to low-frequency motion, T₂ data are of major interest. At temperatures well above the T₁ minimum the small T₂ temperature dependence resembles solidlike behavior reflecting the nonzero averaging of dipolar interactions due to anisotropic motion of the chain segments between crosslinks. The magnitude of T₂ at 60°C is found to be proportional to the average mass between crosslinks.     

Nuclear magnetic relaxation in polyolefin resins

Nuclear magnetic resonance (NMR) spin–lattice relaxation times (T₁) in various polyethylene and polypropylene resins were measured at 20 MHz and at temperatures of 130–490 K. At each temperature and for all resins, only a single value of T₁ was found, which was consistent with the occurrence of rapid spin diffusion throughout the protons attached to the polymer chains. The data were analyzed for the estimation of activation energies corresponding to molecular motion causing spin–lattice relaxation. Two well‐defined minima were found for log_e(T₁) plotted as a function of temperature for all of the polypropylene resins. Single very broad minima were found for all of the polyethylene samples. In contrast, the free induction decay signals from all of the resins following single radio‐frequency pulses were observed to contain a rapidly decaying component followed by a much more slowly decaying signal. These components were used to estimate the amount of rigid component present in the solid resins at room temperature. Samples of one high‐density polyethylene and one low‐density polyethylene were irradiated with γ radiation up to a 500‐kGy dose to examine the effects of crosslinking on the NMR relaxation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 572–584, 2002; DOI 10.1002/polb.10116     

Structural studies of poly(N‐isopropylacrylamide) microgels: Effect of SDS surfactant concentration in the microgel synthesis

Thermoresponsive colloidal microgels were prepared by polymerization of N‐isopropylacrylamide (NIPAM) in the presence of a crosslinking monomer, N,N‐methylenebisacrylamide, in water with varying concentrations (<CMC) of an anionic surfactant, sodium dodecylsulphate (SDS). Volume phase transitions of the prepared microgels were studied in D₂O by ¹H NMR spectroscopy including the measurements of spin–lattice (T₁) and spin–spin (T₂) relaxation times for the protons of poly(N‐isopropylacrylamide) (PNIPAM) at temperature range 22–50 °C. In addition, microcalorimetry, turbidometry, dynamic light scattering, and electrophoretic mobility measurements were used to characterize the aqueous microgels. As expected, increasing SDS concentration in the polymerization batch decreased the hydrodynamic size of an aqueous microgel. Structures with high mobilities at temperatures above the LCST of PNIPAM were observed in the microgels prepared with small amount of SDS, as indicated by the relaxation times of different PNIPAM protons. It was concluded that the high mobility at high temperatures is in connection to a mobile surface layer with polyelectrolyte nature and with high local LCST. High SDS concentration in the synthesis was observed to prevent the formation of permanent, solid PNIPAM particles. The results from different characterization methods indicated that PNIPAM microgels prepared in high SDS concentrations appear to be more homogeneously structured than their correspondences prepared in low SDS concentration. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3305–3314, 2006     

Characterization of blends of poly(vinyl chloride) and poly(N‐vinyl pyrrolidone) by FTIR and 13C CP/MAS NMR spectroscopy

Blends of poly(vinyl chloride) (PVC) with Poly(N‐vinyl pyrrolidone) (PVP) were investigated by Fourier infrared spectroscopy (FTIR) and high‐resolution solid‐state ¹³C cross‐polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. The intermolecular interactions between PVP and PVC are weaker than the self‐association of PVP and the inclusion of the miscible PVC results in the decreased self‐association of PVP chains, which was evidenced by the observation of high‐frequency shift of amide stretching vibration bands of PVP with inclusion of PVC. This result was further substantiated by the study of ¹³C CP/MAS spectra, in which the chemical shift of carbonyl resonance of PVP was observed to shift to a high field with inclusion of PVC, indicating that the magnetic shielding of the carbonyl carbon nucleus is increased. The proton spin‐lattice relaxation time in the laboratory frame (T₁ (H)) and the proton spin‐lattice relaxation time in the rotating frame (T_1ρ(H)) were measured as a function of the blend composition to give the information about phase structure. It is concluded that the PVC and PVP chains are intimately mixed on the scale of 20–30Å. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2412–2419, 1999     

Solid‐state nuclear magnetic resonance relaxation times in crosslinked macroporous polymer particles of divinylbenzene homopolymers

Monodisperse porous particles of poly(divinylbenzene) prepared by the activated swelling method have been investigated by solid‐state ¹³C crosspolarization magic‐angle spinning (CPMAS) nuclear magnetic resonance (NMR) relaxation measurements. Homopolymeric combinations of two porogens (toluene and 2‐ethylhexanoic acid) and two monomers (meta‐ and para‐divinylbenzene) were studied. Residual vinyl groups were systematically reacted with increasing amounts of bromine, producing 20 different polymers samples for which we measured crosspolarization times, T_CH, proton rotating frame spin‐lattice relaxation, T, ¹³C spin‐lattice relaxation, T, and proton spin‐lattice relaxation, T. These parameters were chosen to reflect expected changes in a wide range of frequencies of motion as a function of structure. Relative differences in the molecular mobility of the major functional groups (aromatic, vinyl and aliphatic) is related to initial reactants used, vinyl concentration, relative reactivity of vinyl groups, distribution of vinyl groups, pore structure, and degree of crosslinking. Variable temperature ¹H combined rotation and multiple pulse NMR (CRAMPS) was used to derive activation energies for selected samples via measurement of the proton spin‐lattice relaxation time, T. Irreversible thermal effects were observed in ambient temperature relaxation after heating to temperatures in the range of 393–418 K. Simple univariate statistical analyses failed to reveal consistent correlations among the known variables. However, the application of more sophisticated multivariate and neural network analyses allowed excellent structure–property predictions to be made from the relaxation time data. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1307–1328, 1999     

23Na NMR in urethane cross-linked polyether solid polymer electrolytes

Sodium triflate/polyether urethane polymer electrolytes ranging in concentration from 0.05 molal to 1.75 molal have been investigated via ²³Na static solid-state NMR. Room temperature spectra and spin lattice relaxation times were consistent with a single narrow resonance indicating the presence of only mobile ionic species. The concentration and temperature dependence of relaxation times, chemical shifts, and linewidth have been investigated. The results suggest either a single species or rapid exchange between a number of species (even at temperatures below the glass transition temperature, T_g). The linewidth decreases with increasing concentration of ions and remains temperature independent below T_g. Below T_g a maximum quadrupolar interaction constant of 2 MHz is calculated. The addition of plasticizer to the polymer electrolyte causes significant chemical shift changes that depend on the solvent donicity of the plasticizer. The linewidth and T₁ relaxation times also depend on the T_g of the plasticized systems. Previous ²³Na NMR literature results are reviewed and qualitative models developed to account for the variation in results. © 1994 John Wiley & Sons, Inc.     

Studies on the phase structure of ethylene‐vinyl acetate copolymers by solid‐state 1H and 13C NMR

The phase structure of a series of ethylene‐vinyl acetate copolymers has been investigated by solid‐state wide‐line ¹H NMR and solid‐state high‐resolution ¹³C NMR spectroscopy. Not only the degree of crystallinity but the relative contents of the monoclinic and orthorhombic crystals within the crystalline region varied with the vinyl acetate (VA) content. Biexponential ¹³C NMR spin–lattice relaxation behavior was observed for the crystalline region of all samples. The component with longer ¹³C NMR spin–lattice relaxation time (T₁) was attributed to the internal part of the crystalline region, whereas the component with shorter ¹³C NMR T₁ to the mobile crystalline component was located between the noncrystalline region and the internal part of the crystalline region. The content of the mobile crystalline component relative to the internal part of the crystalline region increased with the VA content, showing that the ¹³C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2199–2207, 2002     

Physicochemical characterization of chemical hydrogels based on PVA

In this paper, we report on the physicochemical characterization of hydrogels recently obtained by crosslinking poly (vinylalcohol), PVA, with telechelic PVA (telPVA, bearing terminal aldehydic groups) via acetalization in aqueous solution. These gels were studied by equilibrium swelling, compression modulus measurements, and proton relaxometry experiments. Swelling and compression modulus data allow to estimate the average molecular weight of PVA chain between crosslinks, the average mesh size of the networks, and the polymer–solvent interaction parameter χ₁. The average mesh size of PVA‐telPVA compares well with domain dimensions of diffusionally confined water as detected by NMR relaxometry. Proton relaxometry also showed different network domains in which water is compartmentalized, indicating a complex heterogeneity. The study of the temperature behavior of the nuclear spin–spin relaxation times of the confined water was also considered. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1225–1233, 1999     

Proton NMR investigation of the local dynamics of PEO in PEO/PMMA blends

Longitudinal relaxation of proton magnetisation was used to characterize the molecular motions of PEO chains in compatible PEO (hydrogenated)/PMMA (deuterated) blends. Both the temperature and the PEO concentration, Φ, were varied. A maximum in the spin–lattice relaxation rate was observed and its properties were analyzed as a function of Φ. For Φ ≤ 0.50, the maximum is observed below the glass transition temperature of the blend; this shows that PEO chains dispersed in a matrix of PMMA remain highly mobile on a local scale even below T_g(Φ). A frequency–temperature correspondence procedure, applied to the measurements performed at two Larmor frequencies, 32 and 60 MHz, leads to a characteristic correlation time for PEO molecular motions. Its temperature dependence obeys a WLF free volume relation above the glass transition of the blends. The PEO free volume fraction and its thermal expansion are strongly reduced by the presence of the PMMA chains. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1095–1105, 1997     

Investigation of molecular motions of crosslinked polyepichlorohydrin by nuclear magnetic resonance spectroscopy

The molecular motion of crosslinked polyepichlorohydrin (PECH) is studied qualitatively by NMR techniques. The results of temperature dependence of ¹H T₂ and T₁ indicate that the crosslinking (crosslink density < 3%) restricts molecular motions of the polymer even far above its T_g. The ¹H T₁ minimum, corresponding to the large-scale chain-motion of crosslinked PECH, shifts to higher temperatures with increasing crosslink density. ¹H T₂ data also show that the crosslinking hinders free chain motions of the polymer above its T_g. The ¹³C T₁ relaxation time is sensitive to such motional changes as well. ¹³C linewidths of crosslinked PECHs vary with the crosslink density in both the swollen state and the solid state. The mechanism of ¹³C linewidth broadening of crosslinked polymers is discussed in detail. In the case of PECH, the linewidth broadening is caused by changing molecular environment due to crosslinking (such as presence of various chemical shift structures and freezing effects in conformational environment as chain mobility decreases), rather than increasing correlation times, which shorten the relaxation time (T₂) of polymer chains. © 1994 John Wiley & Sons, Inc.     

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     

Slow motion in [ring‐fluoro]polycarbonate by CODEX

Chain dynamics in [ring‐fluoro]polycarbonate (an A‐B alternating copolymer that has a single fluorine substituent on every fourth main chain ring) have been characterized by centerband only detection of exchange (CODEX) and rotating‐frame ¹³C spin‐lattice relaxation. The slow motions detected by CODEX are facilitated by a mechanically active lattice reorganization that permits a flip of the fluorinated ring about its C₂ axis. Nonfluorinated rings undergo small‐amplitude reorientations and C₂ flips, both of which are fast and not CODEX active. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1062–1066, 2008     

Segmental and crosslink point motion in networks

¹³C- and ³¹P-NMR spin lattice relaxation in the rotating frame have been measured on a series of networks prepared from monodisperse and deliberately bimodal poly(propylene glycols) (PPG) crosslinked with tris(4-isocyanatophenyl) thiophosphate. The T_1pC minima correspond to loss maxima in the DMTA (Dynamic Mechanical Testing) measured at 10Hz. The T_1p^P minima fall at higher temperatures than those of T_1p^C for the same network indicating that these crosslinks lag the segments in frequency of motion at a given temperature. The carbon relaxation is biphasic below T_g of the segments indicating two relaxation domains which we assign to bulklike PPG segments and PPG segments proximal to he crosslink. Lineshape analysis by a diffusional model indicates crosslink reorientation is not isotropic until well above T_g. Relaxation and lineshapes for the bimodal networks indicate that junctions are not uniformly plasticized by the segments.     

Unexpected proton spin‐lattice relaxation in the solutions of polyolefin and tetrachloroethane

‘Unexpected’ proton spin‐lattice relaxation (T₁) times are reported for the solutions of poly(ethylene‐co‐1‐octene) and tetrachloroethane‐d₂. For the residual protons of the deuterated solvent and the methyl and vinyl protons at the polymer chain ends, their T₁ relaxation times vary significantly with both the polymer concentration and molecular weight over a wide range. The T₁s also decrease with increasing temperature at relative high temperatures. Such behaviors are in contrast to most reported polymer solutions in which the T₁ has nearly no concentration or molecular weight dependence in the dilute and semi‐dilute regime, and normal dependence on temperature. Further investigation revealed that the paramagnetic oxygen effect did shorten the measured proton T₁s, but cannot account for the unexpected T₁ dependences. Spin rotation is proposed to provide a reasonable explanation. Copyright © 2010 John Wiley & Sons, Ltd.     

The structural and dynamic properties of 1‐bromodecane in urea inclusion compounds investigated by solid‐state 1H, 13C and 2H NMR spectroscopy

For asymmetric guest molecules in urea, the end‐groups of two adjacent guest molecules may arrange in three different ways: head–head, head–tail and tail–tail. Solid‐state ¹H and ¹³C NMR spectroscopy is used to study the structural properties of 1‐bromodecane in urea. It is found that the end groups of the guest molecules are randomly arranged. The dynamic characteristics of 1‐bromodecane in urea inclusion compounds are probed by variable‐temperature solid‐state ²H NMR spectroscopy (line shapes, spin–spin relaxation: T₂, spin‐lattice relaxation: T_1Z and T_1Q) between 120 K and room temperature. The comparison between the simulation and experimental data shows that the dynamic properties of the guest molecules can be described in a quantitative way using a non‐degenerate three‐site jump process in the low‐temperature phase and a degenerate three‐site jump in the high‐temperature phase, in combination with the small‐angle wobbling motion. The kinetic parameters can be derived from the simulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Dielectric relaxation studies of aromatic polyamides

Dielectric relaxation spectroscopy (DRS) is presented for a family of four aromatic polyamides trying to relate the structure of the lateral groups to the molecular mobility. A prominent sub-T_g absorption is always seen followed in some cases by remanent dielectric activity at room temperature and a subsequent increase of the loss permittivity. The low temperature relaxation is analyzed in terms of a Fuoss–Kirkwood equation to obtain the broadness and the strength of these relaxations as well as the activation energy (ranging from 10 to 11 Kcal/mol). The low frequency conductive peak shows in each case a half-width higher (1.30) than those corresponding to a single relaxation time peak (1.144). These values of the half-width are an indication of the complex character of these phenomena. A final discussion of the rotational barriers of the lateral chains rules out that such motions are the only molecular origin for the gamma relaxation. Instead, some kind of motion involving the main chain and where the interchain interactions play a significant role should be considered as responsible for that relaxation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 919–927, 1997     

Solid‐state NMR analyses of the crystalline–noncrystalline structure and its thermal changes for ethylene ionomers

The crystalline–noncrystalline structure and its structural changes from thermal treatments for ethylene ionomers have been investigated with solid‐state ¹³C and ²³Na NMR spectroscopy. ¹³C spin–lattice relaxation time (T_1C) measurements reveal that as‐received ethylene ionomers have much enhanced molecular mobility in the crystalline region in comparison with conventional polyethylene samples. By appropriate annealing, however, polyethylene‐like morphological features reflecting T_1C behavior can also be observed. ¹³C spin–spin relaxation time (T_2C) measurements for the noncrystalline region reveal the existence of two components with different T_2C values, and these two components have been assigned to the crystalline–amorphous interfacial and rubbery–amorphous components. These results indicate that the structure of the major part of the noncrystalline region in the ethylene ionomers is similar to that of bulk‐crystallized polyethylene samples, regardless of possible ionic aggregates. The origin of the lower temperature endothermic peak in the heating process of the differential scanning calorimetry curve observed for the as‐received sample has also been examined somewhat in detail. As a result, it is proposed that the melting of smaller crystallites produced during storage at room temperature is the origin of the lower temperature peak. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1142–1153, 2002     

From the SmA to the Hexatic,Including the SmC*, SmC*A and SmC*re Phases: A 2H NMR Relaxation Study

The molecular dynamics of a ferroelectric liquid crystal, denoted ZLL 7/* , is investigated by means of ²H NMR relaxation. The spin–lattice (T_1Q and T_1Z) and spin–spin (T₂) relaxation times of two isotopomers of ZLL 7/* , labeled on the phenyl and biphenyl fragments, are measured and their behavior upon passing from the SmA to the hexatic phase, through the ferroelectric SmC*, antiferroelectric SmC*_A, and re‐entrant ferroelectric SmC*_re phases, is discussed. A comparison between the measured T₂ and T₂*, directly related to the experimental linewidth, provides information on the heterogeneity of the system, thus allowing confirmation of previous hypotheses concerning the structural and ordering properties of the SmC*_A and SmC*_re phases. The possibility to look at different sites of the core of the ZLL 7/* smectogen reveals a peculiar sensitivity of the phenyl moiety with respect to the biphenyl fragment, which may be justified by its vicinity to the chiral centers. Interestingly, the trend of the longitudinal relaxation times is characterized by a minimum that corresponds to the SmC*_A and SmC*_re phases, which is reproducible for the two isotopomers and at several Larmor frequencies. A quantitative analysis of T_1Q and T_1Z is performed in the SmA and SmC* phases, for which the narrowing regime approximation is valid. A multifrequency approach is applied to self‐consistently determine the diffusion coefficients for the overall molecular motions, namely spinning and tumbling, and the internal rotations around the para axes of the phenyl and biphenyl fragments. The effect of the magnetic field in unwinding the helical structure of the SmC* phase (for H>9 T) allows observation of a sensitive change in the rotational diffusion coefficients in the frustrated unwound SmC* phase with respect to the SmC* phase.     

Morphology and dynamics of the poly(ϵ‐caprolactone)‐b‐poly(L‐lactide) diblock copolymer and its inclusion compound with α‐cyclodextrin: A solid‐state 13C NMR study

A biodegradable diblock copolymer of poly(ϵ‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA) was synthesized and characterized. The inclusion compound (IC) of this copolymer with α‐cyclodextrin (α‐CD) was formed and characterized. Wide‐angle X‐ray diffraction showed that in the IC crystals α‐CDs were packed in the channel mode, which isolated and restricted the individual guest copolymer chains to highly extended conformation. Solid‐state ¹³C NMR techniques were used to investigate the morphology and dynamics of both the bulk and α‐CD‐IC isolated PCL‐b‐PLLA chains. The conformation of the PCL blocks isolated within the α‐CD cavities was similar to the crystalline conformation of PCL blocks in the bulk copolymer. Spin–lattice relaxation time (T₁C) measurements revealed a dramatic difference in the mobilities of the semicrystalline bulk copolymer chains and those isolated in the α‐CD‐IC channels. Carbon‐observed proton spin–lattice relaxation in the rotating frame measurements (T_1ρH) showed that the bulk copolymer was phase‐separated, while, in the IC, exchange of proton magnetization through spin‐diffusion between the isolated guest polymer chains and the host α‐CD was not complete. The two‐dimensional solid‐state heteronuclear correlation (HetCor) method was also employed to monitor proton communication in these samples. Intrablock exchange of proton magnetization was observed in both the bulk semicrystalline and IC copolymer samples at short mixing times; however, even at the longest mixing time, interblock proton communication was not observed in either sample. In spite of the physical closeness between the isolated included guest chains and the host α‐CD molecules, efficient proton spin diffusion was not observed between them in the IC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2086–2096, 2005     

Miscibility and interactions in blends of two proton‐donating polymers: Poly(acrylic acid)/poly(p‐vinylphenol) blends

Blends of poly(acrylic acid) (PAA) and poly(p‐vinylphenol) (PVPh) were prepared from N,N‐dimethylformamide (DMF) and ethanol solutions. The DMF‐cast blends exhibited single T_g's, as shown by modulated differential scanning calorimetry, whereas the ethanol‐cast blends had double T_g's. Fourier transform infrared spectroscopy showed that there was a specific interaction between PAA and PVPh in the DMF‐cast blends. The single‐T_g blends cast from DMF showed single‐exponential decay behavior for the proton spin–lattice relaxation in both the laboratory frame and the rotating frame, indicating that the two polymers mixed intimately on a scale of 2–3 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 789–796, 2003