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Solid-state NMR spectroscopy is used to monitor the layer-by-layer (L-B-L) growth of polyelectrolyte multilayers on colloidal silica. The dynamics and conformation of polyelectrolyte multilayers comprised of the weak polycation, poly(allylamine) hydrochloride, and the strong polyanion, poly(sodium-4-styrene sulfonate), assembled at pH 7 and pH 10 were studied by a combination of ¹H and ¹³C NMR measurements. NOESY spectra detect the association of water to the polyanion, while relaxation measurements show that the outermost layer and the water content influence the mobility of the polyelectrolytes and the adsorbed water. Differences in mobility for films assembled at high and neutral pH are explained by the conformation of the polycation during the assembly process. Finally, the strong−weak polyelectrolyte multilayers are compared to a previous NMR study of strong−strong polyelectrolyte multilayers.

Branch contents in sparsely short-chain branched polyethylenes (<C28) and end-group concentrations in linear polyethylenes were investigated by solid- and melt-state ¹³C NMR using model copolymers of 1-octene, 1-octadecene, 1-hexacosene, and linear PE standards. Benchmark measurements were established for single-pulse acquisition under MAS on these melts at 423 K, using 7 mm ceramic rotors and commercially available solid-state probes at 300 and 500 MHz ¹H Larmor frequency. Signal improvement by a factor of 3−4 was observed, corresponding to a factor 10 reduction in measurement time, when compared to a reference solution-state (400 MHz ¹H) measurement. Transient NOE effects due to proton decoupling during FID acquisition were found to affect significantly the accuracy of branch content determination and end-group analysis in the melt spectra, even at moderate pulse repetition rates. ¹³C T1 and NOE buildup rates and intensity variations were established at 423 K and correlated to the local packing of the branched chain architecture. CP/MAS spectra at and below room temperature on the solid-state polyethylenes showed good agreement with reference spectra, providing an alternative method for sensitivity improvement, with about a factor of 10 saving in measurement time as compared to the melt measurements. Using an optimized parameter set, molecular weight determination of a linear polyethylene standard with Mn>100 000 g/mol was shown to be feasible in both solid-state and melt measurements in less than a one-day measurement, obtained on a 500 MHz spectrometer and 4 mm rotor. Using this enhanced signal intensity, NMR relaxation times were investigated in the melt with respect to their inherent sensitivity to the branching architecture. These measurements included T1ρ, T1, and T1^NOE. It was found that T1^NOE seems to have the best sensitivity to determine the approximate length of the side chain branches for n > 6.

Bicomponent nanophase-separated poly(2-hydroxyethyl methacrylate)-linked-polyisobutylene (PHEMA-l-PIB) amphiphilic conetworks were synthesized by radical copolymerization of methacrylate−telechelic polyisobutylene (MA−PIB−MA) and different amounts of 2-(trimethylsilyloxy)ethyl methacrylate (SEMA) followed by quantitative hydrolysis of the trimethylsilyl protecting groups. The PIB content of the resulting conetworks, determined by elemental analysis and solid-state ¹H NMR under fast magic-angle spinning (MAS), varied between 17 and 63% w/w. Phase separation and morphology of these conetworks were investigated by DSC, small-angle X-ray scattering (SAXS), and for the first time by ¹H spin diffusion solid-state NMR. Two Tg values were observed by DSC in all samples. The observed Tg values were close to the literature values of both homopolymers (110 °C for PHEMA and −67 °C for PIB), indicating a strong phase-separated morphology in these conetworks. Parameters were optimized for the ¹H spin diffusion NMR experiments, and the measurements were carried out with six filtering cycles and a 10 μs delay between pulses at 90 °C. The NMR and SAXS measurements prove strong phase-separated morphology. The sizes of the hydrophilic (PHEMA) and hydrophobic (PIB) nanodomains were determined to be in the 5−15 nm range. The spin diffusion experiments also indicate strongly separated phases without a detectable interface with mixed components. The long period of our system seems to depend weakly on the volume fraction whereas the morphology of the nanophases depends on the volume fraction.

Counterion condensation of multivalent, charged spin probes to highly charged cationic and anionic polyelectrolytes is characterized by CW and FT EPR spectroscopy. Line broadening and deviation from Lorentzian line shape in the EPR spectra of the spin probes are observed upon addition of the polyelectrolyte. These effects are due to dynamic electrostatic attachment of the counterions with exchange between the condensed and free states on a subnanosecond time scale. The spectral changes can be separated into a contribution due to slowdown of rotational dynamics and a contribution due to enhanced spin exchange. A drastic increase of the spin-exchange contribution is observed upon increasing the concentration of two anionic spin probes in aqueous solutions of the cationic polyelectrolyte poly(diallyldimethylammonium chloride), PDADMAC. This can be traced back to a counterion-induced chain collapse which is, however, not observed in mixtures of water with organic solvents of either higher (N-methylpropionamide) or lower (ethanol) permittivity. Simple polyelectrolyte theory, which considers solvents only as a dielectric continuum, cannot explain these findings. Screening of hydrophobic interactions between repeat units of the chain by the organic solvents is suggested as an explanation.

High-resolution proton double-quantum (DQ) magic-angle spinning (MAS) NMR is used as a new technique that is capable of revealing complex motional processes in entangled polymer melts. Theoretical analysis shows the connection of quantities relating anisotropic polymer dynamics to data obtained from our DQ-MAS NMR experiment. With this technique, dynamic chain ordering as well as scaling laws consistent with the reptation model was previously observed for polybutadiene (PB). Here, the influence of rigid confinements represented by immobile moieties attached to one or both chain ends of the PB block on chain dynamics and ordering are investigated. Symmetric poly(styrene-b-butadiene) diblock copolymers (PS-b-PB) with varying molecular weights are examined as systems with one anchored chain end. As materials with two tethered chain ends PS-b-PB-b-PS triblock copolymers are studied. In these systems, the effects of rigid confinements on the polymer dynamics in the melt are analyzed. We find that dynamic order parameters are increased by more than a factor of 2 for block copolymers compared to homopolymers. Furthermore, on account of the chemical constraints imposed on the PB block, the lack of the motional regime that involves diffusive reptation motion is experimentally confirmed. Correspondingly, the scaling law pattern differs qualitatively from those observed for PB homopolymers.

¹⁹F NMR experiments are used to study the aggregation behavior of two telechelic polymer systems. These polymer systems consist of a water−soluble chain, here poly(ethylene glycol), with two hydrophobic endgroups. Because of the hydrophobic interaction of the fluorocarbon endgroups, these polymer chains associate in water to form aggregates at low concentrations. The aggregate comprises a core formed from the insoluble hydrophobic endgroups that are surrounded by a corona of long water-soluble polymer chains. With increasing polymer concentration, the polymer chains start bridging so that a three-dimensional, physical network with fluorinated aggregate cores as cross-link points is formed. This effect can be substantially enhanced by replacing the hydrophobic endgroup C6F13 with C8F17, a consequence of the stronger association of C8F17 in aqueous solution. By different ¹⁹F NMR parameters, i.e., ¹⁹F transverse relaxation and ¹⁹F chemical shift, we can distinguish aggregated and nonaggregated chain ends. This enables us to follow the formation of an infinite network.

Solid-state ¹H NMR spin diffusion experiments are useful tools for the elucidation of domain sizes of heterogeneous polymers. For quantitative determination of domain sizes, however, reliable values of the spin diffusion coefficients are required. In this paper, spin diffusion coefficients are calibrated for mobile polymers through the transverse relaxation rate T2^-1 of ¹H magnetization measured by a Carr−Purcell−Meiboom−Gill sequence. Different regimes were observed for T2^-1 below and above 1 kHz.

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, provide the conditions necessary for elimination of viscous dissipation. These findings require refinement of the previously held view that the transition around 45 °C in PMP denotes a glass transition associated with the onset of rapid backbone segmental motions.

Core−shell latexes based on poly(butyl acrylate) and poly(methyl methacrylate) and latexes of poly(butyl acrylate) and polystyrene were synthesized at high and low temperatures. In both cases the shell content was 33% in weight. Transmission electron microscopy and advanced NMR techniques have been used to investigate the structure of the system, and particular emphasis was put on the characterization of the interface between the two components. This interface can sensitively be analyzed using ¹H spin-diffusion techniques. Dynamic gradients at the interface are detected with varying filter strengths of the dipolar filter selecting mobile components and 2D wideline separation (WISE) NMR spectra in which structural and dynamic information are correlated. These experiments show distinct differences in the interface structure of systems synthesized at different temperatures and those with poly(methyl methacrylate) or polystyrene in the shell, respectively.