Wideline Separation Research Articles

Phase Behavior and Segmental Mobility in Binary Blends of Polystyrene and Poly(vinyl methyl ether)

The phase behavior and segmental mobility in binary blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) were investigated. Two nearly monodisperse PSs having weight-average molecular weights (Mw) of 57 000 and 95 000 with polydispersity indexes (PDI) of 1.06 and 1.09, respectively, and PVME having Mw = 99 000 with a PDI of 2.13 were used for this study. Two sets of PS/PVME binary blends with varying compositions were prepared by solvent casting from toluene. Thermograms from differential scanning calorimetry showed that each blend has a single, yet very broad glass transition temperature. Cloud point measurements via He−Ne laser light scattering were taken to determine phase equilibria in each blend, which exhibited lower critical solution temperature (LCST) behavior. Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to examine segmental mobility and component domain sizes. 1H T1ρ experiments were run at temperatures ranging from −40 to 140 °C. We observed only small differences in 1H T1ρ values of PS and PVME at temperatures below 45−80 °C (depending on blend composition) and a large divergence of 1H T1ρ values at higher temperatures. 13C T1ρ and wide-line separation (WISE) experiments were run at room temperature on untreated and heat-treated samples. WISE experiments revealed that heterogeneities from 3.5 nm to greater than 30 nm existed within the blends, depending on the temperature of heat treatment. Since it has been found that 1H T1ρ measurements can give ambiguous domain information, 1H-NOESY NMR was used to examine several blend compositions at 100 °C. We conclude from this study that nanoheterogeneities exist in these PS/PVME blends at temperatures below the binodal curve determined by cloud point measurements and that a broad, single glass transition should not be construed as evidence of miscibility at the molecular level. It has been shown that nanoheterogeneities exist on a segmental level and that there are large changes in mobility at temperatures above 45−80 °C. However, the blend does not phase separate until the critical temperature (LCST), determined by cloud point measurements, is reached.

Characterization of Polyalkylvinyl Ether Phases by Solid-State and Suspended-State Nuclear Magnetic Resonance Investigations

Pure organic polyalkylvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C4VE) and n-octadecylvinyl ether (C18VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and 1H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of 1H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the 1H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin–lattice relaxation times (T1) as well as accumulation of a 2D wide line separation NMR spectrum.

WIM/WISE NMR Studies of Chain Dynamics in Solid Polymers and Blends

Wideline separation (WISE) NMR with windowless isotropic mixing (WIM) is developed as a method to study the dynamics of polymers and blends. This experiment is designed to measure the dynamics of polymers through the proton lineshapes that are correlated with the carbon chemical shifts in two-dimensional NMR experiments. If the atoms experience large amplitude fluctuations that are fast compared to the dipolar broadening, then the proton lines will be narrowed relative to rigid solids. We have modified the WISE experiment by replacing the cross polarization step with WIM to quench spin diffusion during the cross polarization so that the proton linewidths can be directly related to the chain dynamics. Two-dimensional WIM/WISE has been used to measure the main-chain and side-chain dynamics in poly(n-butyl methacrylate) and blends of polystyrene and poly(vinyl methyl ether).

13C-Detected1H Spin Diffusion and1H Relaxation Study of Multicomponent Polymer Blends

The miscibility of two macroscopic phase separated polymers, a propylene−ethylene−diene terpolymer and an atactic polypropylene, has been investigated by a combination of several solid-state NMR techniques. Carbon-detected proton T1ρ and carbon-detected proton T1 in systems conditioned by two-dimensional heteronuclear wide-line separation (WISE) were used. Both techniques are sensitive to spin diffusion between phases, with WISE being suited to making it stand apart from the basic relaxation process. These two techniques yield similar but different assessments of the presence and amount of phase separation present. This is not surprising considering that they involve different relaxation time scales, from milliseconds to seconds. An additional comparison is made with differential scanning calorimetry and xenon NMR results, which also address this problem. In addition, the WISE data permit an estimate of the aPP domain size.

Solid-state NMR characterization of hydration effects on polymer mobility in onion cell-wall material

The effect of hydration on the mobility of polysaccharides in onion cell-wall material (CWM) was studied by solid-state NMR. The application of proton T 1ρ, carbon T 1 relaxation measurements, and 2D-WISE (wideline separation) experiments led to a coherent overall picture of the mobility inside the cell wall, combining domain-averaged as well as site-specific motional information. Whereas the mobility of all individual chemical sites increased upon hydration, only the average chain mobility of the pectin was strongly affected, indicating the predominant interaction of water molecules with the pectin. The 2D-WISE experiment revealed a spatial heterogeneity of the polysaccharide dynamics across the sample, showing at least two different motional regimes for pectin and cellulose domains.

Fast Magic-Angle Proton NMR Studies of Polymer Interfaces in Poly(ethyl acrylate)/Vycor Composites

Fast magic-angle spinning solid-state proton NMR has been used to study the structure and dynamics of poly(ethyl acrylate) in bulk and polymerized in a Vycor glass with 40 A pores. Bulk poly(ethyl acrylate) is a low-T g material, and high-resolution solid-state proton NMR spectra are observed at ambient temperature because the dipolar interactions are averaged by the combination of chain motion and fast magic-angle sample spinning. The spectrum of the poly(ethyl acrylate)/Vycor composite shows signals in addition to those of the polymer that are assigned to water and surface hydroxyl groups in the porous glass. Integration of the composite and bulk poly(ethyl acrylate) signals reveals that the volume fraction of polymer in the pores is 0.56 and that the polymer occupies the central 30 A in a 40 A pore. Spin diffusion studies demonstrate that filling of the poly(ethyl acrylate)/Vycor is incomplete, and a fraction of the water in the pores is isolated from the polymer. Multiple-quantum NMR studies reveal a large difference in chain dynamics between the bulk poly(ethyl acrylate) and the porous glass composite, and 2D wide line separation NMR shows that the polymer is restricted at the surface of the pores but has bulklike mobility in the center of the pore.

Microphase Structures of Poly(styrene-b-ethylene/propylene) Diblock Copolymers Investigated by Solid-State NMR and Small-Angle X-ray Scattering Techniques

The microphase structures of two commercial polystyrene-b-poly(ethylene/propylene) diblock copolymers with different compositions and molecular weights have been studied by solid-state NMR and small-angle X-ray scattering (SAXS) techniques. The nearly homogeneous narrow proton line shape of the rubber peaks in the two-dimensional wide-line separation (WISE) spectrum indicates that the interfacial region between the rigid polystyrene and the mobile rubber phases is small compared with the size of the domains. 1H spin diffusion measurements were used to measure the sizes of various domains and the interface between them using a model that considers the effects of 1H spin−lattice relaxation. The thickness of the interface determined by NMR is about 2 nm for both copolymers. Interdomain distances measured by NMR agree well with the results of SAXS measurements and increase with the increase of the molecular weight of the copolymers. However, the sizes of dispersed polystyrene domains obtained from NMR are sma...

Architecture and Dynamics of C22 Bonded Interphases

The relationship between alkyl phase structure and chromatographic performance is investigated for a series of docosyl (C22)-modified silica surfaces. The results of solid-state nuclear magnetic resonance (NMR) spectroscopy and fluorescence spectroscopy are evaluated and correlated with liquid chromatographic retention for relevant shape-selective separations. A set of four different stationary phases was prepared by solution and surface polymerization approaches, yielding materials with surface coverages ranging from 3.6 to 7.0 μmol/m2. 13C cross polarization magic angle spinning (CP/MAS) NMR spectra indicate that a predominance of trans conformations exists for high-coverage C22 phases (>4.0 μmol/m2). Two-dimensional solid-state NMR spectroscopy (wide line separation, WISE) was utilized to evaluate the mobility of the trans and gauche alkyl chain conformations. Temperature-dependent 13C CP/MAS NMR measurements of the bonded phases exhibit large differences in the dynamic behavior of the immobilized C22 chains. Unusually high chain rigidity was found for the self-assembled monolayer C22 phase (7.0 μmol/m2). Fluorescence lifetime measurements of 1,6-diphenylhexatriene (DPH) exhibit two different lifetimes of τF ≈ 1 and 7 ns, which are ascribed to probe molecule populations in the mobile and bonded phases, respectively. Quantitative evaluation of the fluorescence decay curves shows that the partitioning of DPH into the alkyl phase is favored at higher surface coverages, reaching a maximum at a ligand density of 4.9 μmol/m2. Time-resolved fluorescence anisotropy measurements also revealed that probe mobility was minimized at this surface coverage. With increasing temperature, the mobility of DPH was found to increase and the fraction of sorbed molecules to decrease. A shape selectivity test mixture containing five polycyclic aromatic hydrocarbons including DPH was employed for temperature-dependent chromatographic studies. In accord with the spectroscopic results, shape selectivity is enhanced at low temperatures and at high surface coverages. The combination of these spectroscopic and chromatographic tools provides a wealth of information on the surface morphology of systematically prepared C22 sorbents and greater insight on the molecular recognition process in liquid chromatography.

Structure of Styrene Grafted Poly(vinylidene fluoride) Membranes Investigated by Solid-State NMR

The poly(vinylidene fluoride), PVDF, membranes that have been radiation grafted with polystyrene, PS, producing PVDF-g-PS membranes, are intermediates in the synthesis of PVDF-g-polystyrenesulfonic acid (PSSA) polymer electrolyte membranes. Solid-state NMR measurements were carried out to study the structure of the PVDF-g-PS membranes. The previous investigations by thermal methods and by X-ray scattering showed phase separation of the two polymeric components. The extent of phase separation and the mobility of the components in the membranes were investigated by NMR relaxation time measurements and by 2-D wide-line separation (WISE) experiments. It was shown that the amorphous PVDF and PS are phase separated into domains larger than several nanometers. The amorphous PVDF component also retained higher mobility than the PS. Information on the structure of the intermediate product can be used when interpreting the properties of the final polymer electrolyte membrane.

Conformation of spacers in smectic poly(ester imide)s

Several poly(ester imide)s based on 4-N-(carboxyphenyl)trimellitimide, 4- N-(carboxyethenylphenyl)trimellitimide, 4-hydroxy-N-(4-hydroxyphenyl)phthalimide and long aliphatic spacers have been investigated by different solid-state NMR tech- niques. The conformations of the methylene units were studied by the g-gauche effect of the 13 C chemical shift. In the frozen smectic LC phase, an alternating sequence of trans-conformations and disordered segments is predominant. In contrast, the spacers in the smectic-crystalline phase are capable of forming ordered trans-trans conforma- tions. The amount of tt-conformations is found to increase with the spacer length and depend on the packing of the mesogens and the type of linkage between mesogen and spacer. The thermal stability above 1007C and the segmental mobility of the tt- conformations, as measured by 13 C/ 1 H wide line separation NMR, suggest a ropelike arrangement of the spacers. The tt-sequences are located in the outer parts rather than in the center of the spacer layer. Dephasing delay experiments on analogous polymers, which are deuteriated selectively in the four central methylene groups of the spacers, prove that these segments do not contain tt-conformations. Consequently, the ordering is due to the molecular constrains exerted by the rigid mesogenic groups and not by lateral van der Waals interactions between adjacent spacer segments. In a random copolymer with two different spacer lengths, the shorter spacer is found to be more extended than in the corresponding homopolymer. q 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2033-2046, 1998

Solid-state NMR studies of structure and dynamics of erucamide/isotactic poly(propylene) blends

Solid-state NMR spin diffusion experiments and two-dimensional (2D) 1 H- 13 C NMR experiments have been used to study the phase structure, mobility and domain sizes of blends of isotactic poly(propylene) (i-PP) and erucamide (ERU), a low molecular weight slip and antiblock additive for i-PP films. The study of the proton line shapes in pure erucamide and i-PP together with their blends reveals the mobility of the two components. The mobility is higher in the blends than in erucamide and i-PP when they are considered separately. In addition, 2D wideline separation (WISE) NMR spectroscopy indicates that erucamide molecules show both low and high mobilities depending on the erucamide content in the blend. By measuring the proton spin diffusion with 'H detection, the microdomain dimensions have been estimated quantitatively. The domain sizes range from approximately 13 nm to 60 nm.

Solid-state NMR studies of structure and dynamics of erucamide/isotactic poly(propylene) blends

Solid-state NMR spin diffusion experiments and two-dimensional (2D) 1H-13C NMR experiments have been used to study the phase structure, mobility and domain sizes of blends of isotactic poly(propylene) (i-PP) and erucamide (ERU), a low molecular weight slip and antiblock additive for i-PP films. The study of the proton line shapes in pure erucamide and i-PP together with their blends reveals the mobility of the two components. The mobility is higher in the blends than in erucamide and i-PP when they are considered separately. In addition, 2D wideline separation (WISE) NMR spectroscopy indicates that erucamide molecules show both low and high mobilities depending on the erucamide content in the blend. By measuring the proton spin diffusion with 1H detection, the microdomain dimensions have been estimated quantitatively. The domain sizes range from approximately 13 nm to 60 nm.

A WISE NMR Approach to Heterogeneous Biopolymer Mixtures: Dynamics and Domains in Wounded Potato Tissues

Two-dimensional 1H−13C wide-line separation (WISE) NMR, a technique developed for the characterization of synthetic copolymers and blends in the solid state, has been used to study the dynamic behavior and domain structure of the biopolymer suberin deposited within the wound periderm of potato tubers. This blend consists of cell-wall polysaccharides and cross-linked aromatic−aliphatic polyesters that regulate water transport and protect the plant tissue from pathogenic attack. Though most of the suberin chemical moieties are rigid, about 20% of its chain-methylene groups exhibit surprising flexibility on the 50-kHz frequency scale. The resulting motional narrowing is propagated rapidly by spin diffusion to other residues within the suberin domain, but much more slowly to the spatially separated cell-wall region. Using a selective spin-diffusion experiment with a dipolar filter, the suberin domain size has been estimated as 50 nm and compared with prior results from electron microscopy. Finally, the resist...

Microphase separation in RIM polyureas as studied by solid-state NMR

The microphase separation (MPS) in polyureas based on methylene diphenyl diisocyanate (MDI) hard segment, diethyltoluenediamine chain extender, and amino-terminated polypropylene glycol soft segment prepared by reaction injection molding (RIM) was studied by advanced solid-state NMR spectroscopy. Incomplete microphase separation leads to the presence of mobilized hard segments dispersed in the soft segment domains as well as immobilized soft segments residing in the hard domains. This is detected by 1H-NMR spectra recorded under spinning at the magic angle (MAS) as well as two-dimensional wide-line separation (WISE) NMR spectra. The sizes of the various domains as well as the interfaces between them are quantified by spin diffusion measurements. In this way the impact of annealing, method of polymerization, and hard segment content on MPS is studied. Whereas annealing at temperatures up to 170°C results in improving the MPS, major changes are observed after annealing at higher temperatures (190°C), where the system changes from “soft-in-hard” to “hard-in-soft” behavior. The MPS decreases with increasing hard segment content. The highest MPS is observed for solution polymerized samples. The various NMR experiments clearly reveal the nonequilibrium nature of RIM systems. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 693–703, 1998

Cross-polarization dynamics and proton dipolar local field measurements in some organic compounds

Hartmann–Hahn inversion–recovery cross-polarization magic-angle spinning experiments were performed for all types of protonated carbons (CHn with n=1, 2 and 3). The resulting non-exponential decays were analyzed using both a simple memory function approach and density matrix calculations. Although the memory function approach provides a useful analytical description of the cross-polarization dynamics, the density matrix method is required to account better for the details of the spin dynamics. 13C-detected dipolar local fields of protons were measured using the wideline separation experiment. It was observed that the resulting local free induction decays may be quantitatively described by their local second moment. Moreover, the local spin diffusion process controlling the second stage of the cross-polarization dynamics is directly related to the strength of the local dipolar field of protons. © 1997 John Wiley & Sons, Ltd.

Structural Correlation Study of Pulsed Plasma-Polymerized Fluorocarbon Solids by Two-Dimensional Wide-Line Separation NMR Spectroscopy

Two-dimensional wide-line separation (WISE) NMR spectroscopy has been applied to obtain structural correlation in fluorocarbon films deposited via a pulsed plasma enhanced chemical vapor deposition...

Structure and Temperature-Dependent Properties of Poly(4-methyl-1-pentene) Fibers

The origin of a dramatic loss of tensile strength in poly(4-methyl-1-pentene) [PMP] above a major dynamic mechanical transition that occurs around 45 °C is explored. The usual mechanisms associated with loss of strength in polymers are shown to be absent in this case. Viscous dissipation disappears almost completely during deformation of PMP above the transition of interest here. A thermodynamic analysis of reversible deformation is shown to provide remarkably good predictions of the work of rupture under such conditions. The thermorheological responses of PMP suggest that the transition of concern here is not accompanied by the onset of rapid backbone motions but by pendant group motions. Indeed, 2D wideline separation (WISE) NMR, which correlates dynamics (via 1H widelines) with structure (via 13C chemical shifts), clearly reveals that this transition is primarily accompanied by the onset of rapid pendant group motions. Such motions, coupled with the relatively large inter-backbone distances in PMP, pro...

Structure and dynamics of polyelectrolyte‐surfactant complexes as revealed by solid state NMR

Abstract13C‐CP/MAS‐NMR (cross‐polarization magic angle spinning), 2D‐WISE (wideline separation experiment) and 1H‐spin diffusion experiments allow to gain new insight into the structure and dynamics of solid polyelectrolyte‐surfactant complexes, a material with pronounced mesophase formation. Experiments were performed on two different complexes of polystyrene sulfonate and octadecyltrimethylammonium or tetradecyltrimethylammonium counterions, PSS‐C18 and PSS‐C14. The strong mobility differences between the ionic and alkyl phase in the lamellar complex PSS‐C18 are reflected in the NMR behavior: in the surfactant tails, a mobility gradient towards the terminal methyl group is observed. This fact as well as a high content of gauche conformations suggest a non‐interdigitating morphology of the tails at room temperature. The behavior changes during cooling below an endothermic transition centered at 255 K where a high trans content and a homogenization of the side chain dynamics is observed. We attribute this transition which is invisible in the X‐ray experiments to the formation of a highly transoid, interdigitated phase of the surfactant tails which is however not crystallized in a classical sense. 1H‐spin diffusion experiments allow to estimate the distance between mobile and immobile regions of the sample. For the complex PSS‐C14, the length scale determined by NMR is essentially that of the primary lamellar structure. For PSS‐C18, a characteristic length of the density fluctuations within the proposed undulated lamellar structure is estimated.

Proton-fluorine wideline separation experiments on poly(vinylidene difluoride)

Two-dimensional heteronuclear proton-fluorine correlation solid-state spectroscopy is demonstrated on a sample of poly(vinylidene difluoride) (PVDF). This allows the correlation of structural information contained in the fluorine chemical shift in one dimension with information on mobility from proton wideline spectra in the second dimension. The effect of the heteronuclear fluorine-proton dipolar coupling on the proton linewidth is investigated separately. The incorporation of magnetization filters into the preparation period enables one to measure the wideline separation (WISE) spectra for the amorphous or the crystalline parts of the sample separately.

Variable-Temperature Solid-State 13C NMR Studies of Nascent and Melt-Crystallized Polyethylene

Nascent and melt-crystallized ultrahigh molecular weight polyethylene (PE) have been studied using solid-state 13 C NMR spectroscopy. Significant differences between the two materials are observed in the CPMAS spectra particularly at elevated temperatures. Three separate resonances are observed in nascent samples when the temperature is raised to near the melting point, the third peak being of an intermediate chemical shift between the crystalline and amorphous resonances that are observed in the spectra of melt-crystallized samples. Based on this chemical shift, the third resonance is likely due to polymer chains which undergo conformational averaging which is intermediate between the rigid all-trans crystalline polymer and very mobile amorphous chains. Evidence is reported which shows that this is material that is present in nascent PE below the melting point and is not created during the melting process. These observations are confirmed by the measurement of 2D wide-line separation (WISE) experiments where the 1 H line width of the amorphous component of melt-crystallized PE is much narrower than that of a nascent sample. Numerous nascent PE samples, including those of low molecular weight, display similar spectral features