Reduced-mobility layers with high internal mobility in poly(ethylene oxide)-silica nanocomposites

© 2017 Author(s). A series of poly(ethylene oxide) nanocomposites with spherical silica was studied by proton NMR spectroscopy, identifying and characterizing reduced-mobility components arising from either room-temperature lateral adsorption or possibly end-group mediated high-temperature bonding to the silica surface. The study complements earlier neutron-scattering results for some of the samples. The estimated thickness of a layer characterized by significant internal mobility resembling backbone rotation ranges from 2 nm for longer (20 k) chains adsorbed on 42 nm diameter particles to 0.5 nm and below for shorter (2 k) chains on 13 nm particles. In the latter case, even lower adsorbed amounts are found when hydroxy endgroups are replaced by methyl endgroups. Both heating and water addition do not lead to significant changes of the observables, in contrast to other systems such as acrylate polymers adsorbed to silica, where temperature- and solvent-induced softening associated with a glass transition temperature gradient was evidenced. We highlight the actual agreement and complementarity of NMR and neutron scattering results, with the earlier ambiguities mainly arising from different sensitivities to the component fractions and the details of their mobility

Ion Transport Properties and Ionicity of 1,3-Dimethyl-1,2,3-Triazolium Salts with Fluorinated Anions

1,2,3-Triazolium salts are an important class of materials with a plethora of sophisticated applications. A series of three novel 1,3-dimethyl-1,2,3-triazolium salts with fluorine, containing anions of various size, is synthesized by methylation of 1,2,3-triazole. Their ion conductivity is measured by impedance spectroscopy, and the corresponding ionicities are determined by diffusion coefficients obtained from 1H and 19F pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy data, revealing that the anion strongly influences their ion conductive properties. Since the molar ion conductivities and ionicities of the 1,3-dimethyl-1,2,3-triazolium salts are enhanced in comparison to other 1,2,3-triazolium salts with longer alkyl substituents, they are promising candidates for applications as electrolytes in electrochemical devices

Polymer Networks Synthesized from Poly(Sorbitol Adipate) and Functionalized Poly(Ethylene Glycol)

Polymer networks were prepared by Steglich esterification using poly(sorbitol adipate) (PSA) and poly(sorbitol adipate)-graft-poly(ethylene glycol) mono methyl ether (PSA-g-mPEG12) copolymer. Utilizing multi-hydroxyl functionalities of PSA, poly(ethylene glycol) (PEG) was first grafted onto a PSA backbone. Then the cross-linking of PSA or PSA-g-mPEG12 was carried out with disuccinyl PEG of different molar masses (Suc-PEGn-Suc). Polymers were characterized through nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The degree of swelling of networks was investigated through water (D2O) uptake studies, while for detailed examination of their structural dynamics, networks were studied using 13C magic angle spinning NMR (13C MAS NMR) spectroscopy, 1H double quantum NMR (1H DQ NMR) spectroscopy, and 1H pulsed field gradient NMR (1H PFG NMR) spectroscopy. These solid state NMR results revealed that the networks were composed of a two component structure, having different dipolar coupling constants. The diffusion of solvent molecules depended on the degree of swelling that was imparted to the network by the varying chain length of the PEG based cross-linking agent

Molecular Dynamics in the Crystalline Regions of Poly(ethylene oxide) Containing a Well-Defined Point Defect in the Middle of the Polymer Chain

The chain mobility in crystals of a homopolymer of poly­(ethylene oxide) (PEO) with 22 monomer units (PEO₂₂) is compared with that of a PEO having the identical number of monomer units but additionally a 1,4-disubstituted 1,2,3-triazole (TR) point defect in the middle of the chain (PEO₁₁–TR–PEO₁₁). In crystals of PEO₂₂, the characteristic α_<i>c</i>-relaxation (helix jumps) is detected and the activation energy of this process is calculated from the pure crystalline ¹H FIDs to 67 kJ/mol. PEO₁₁–TR–PEO₁₁ exhibits a more complex behavior, i.e. a transition into the high temperature phase HTPh is noticed during heating in the temperature range between −5 and 10 °C which is attributed to the incorporation of the TR ring into the crystalline lamellae. The crystal mobility of the low temperature phase LTPh of PEO₁₁–TR–PEO₁₁ is in good agreement with PEO₂₂ since helical jump motions could also be detected by analysis of the ¹H FIDs and the corresponding values of their second moments <i>M</i>₂. In contrast, the high temperature phase of PEO₁₁–TR–PEO₁₁ shows a completely different behavior of the crystal mobility. The crystalline PEO chains are rigid in this HTPh on the time scale of both, the ¹H time-domain technique and in ¹³C MAS CODEX NMR spectroscopy, i.e. the α_<i>c</i>-mobility of PEO in the HTPh of PEO₁₁–TR–PEO₁₁ is completely suppressed and the PEO₁₁ chains are converted into a crystal-fixed polymer due to the incorporation of the TR rings into the crystal structure. However, the TR defect of PEO₁₁–TR–PEO₁₁ shows in the HTPh characteristic π-flip motions with an Arrhenius type activation energy of 223 kJ/mol measured by dielectric relaxation spectroscopy. This motion cannot be observed by corresponding ¹³C MAS CODEX NMR measurements due to an interfering spin-dynamic effect

Chain Dynamics and Segmental Orientation in Polymer Melts Confined to Nanochannels6215

We study changes in the dynamics of polymer chains confined to cylindrical nanochannels within aluminum oxide membranes. Specifically, a proton time-domain NMR technique is used to assess the effect of transient wall contacts on the time-averaged orientational order of poly(butadiene) segments in melts with different molecular weights (MW). Previous work has evidenced that the weakly interacting polymer, residing in ∼100 μm long, 20 and 60 nm wide channels, shows no significant confinement-related changes in the segmental (α) relaxation time and only weak (less than a factor of 2) changes in the micrometer-scale diffusivity. In the relevant temperature range above 340 K, we here use samples with pores oriented at different angles with respect to the main magnetic field to study the macroscopic anisotropy of segmental rotations and the effect of slower motions in regimes III and IV of the tube model up to the milliseconds time scale. We show that the pore walls exert a significant orientation effect on the chains, measured in terms of a time-averaged order parameter with a related length scale of one to a few nanometers, coexisting for high molecular weight (MW) inhomogeneously with bulk-like behavior in the pore center. Low MW with fewer than about 10 entanglements as well as low MW liquids exhibit a homogeneous response, with an overall residual orientation that represents a diffusively averaged quantity reflecting the pore geometry. We support our findings by a simulation model based upon one-dimensional curvilinear chain diffusion along the primitive path. The study is complemented by deuterium NMR experiments on a labeled poly(dimethylsiloxane) sample, in which strong surface contacts prevent full diffusive averaging

Solid State Phase Transitions in Poly(ethylene oxide) Crystals Induced by Designed Chain Defects

We have used Cu­(I)-catalyzed azide–alkyne cycloaddition to synthesize a new series of poly­(ethylene oxide)­s having in the center of their chains two 1,2,3-triazole (TR) rings separated by (CH₂)_<i>n</i> spacers with 2 ≤ <i>n</i> ≤ 4 (PEO₁₁-TR-(CH₂)_<i>n</i>-TR-PEO₁₁). The degree of crystallinity obtained by temperature-dependent WAXS measurements indicates that only one out of the two PEO₁₁ chains of the three polymers forms a 7₂ helix upon cooling to −10 °C and crystallizes into a monoclinic unit cell known from PEO homopolymer. A solid-state phase transition occurs for all samples during heating below their melting temperature. Solid-state ¹³C MAS cross-polarization and single-pulse NMR spectroscopy indicate the complete incorporation of the chain defects into the PEO crystals (PEO-TR phase) during this transition. The 2D WAXS pattern of an oriented PEO₁₁-TR-(CH₂)₂-TR-PEO₁₁ sample generates a structural model where the crystal lattice of the initial PEO phase becomes highly distorted during the solid-state phase transition due to C–H···π interactions of the aromatic TR rings. Furthermore, an additional phase transition occurs for PEO₁₁-TR-(CH₂)₄-TR-PEO₁₁ after melting of the PEO-TR phase. This phase has complex characteristics; i.e., the typical 7₂ helix of PEO forms, but the two TR rings and the methylene groups of the alkyl spacer are in different chemical environments

Chain Tilt and Crystallization of Ethylene Oxide Oligomers with Midchain Defects

Many text books and publications do not focus on the necessity of chain tilting in crystalline lamellae of oligomers and polymers, a fundamental aspect of their crystallization already discussed by Flory. Herein we investigate the chain tilt of ethylene oxide oligomers (EOs) containing various midchain defects by WAXS, SAXS and solid state ¹³C MAS NMR spectroscopy. At low temperatures, one out of the two EO chains of EO₉-<i>meta</i>-EO₉ and EO₁₁-TR-EO₁₁ containing a 1,3-disubstituted benzene or a 1,4-disubstituted 1,2,3-triazole defect in central position of the oligomer chain forms crystals and the other EO chain as well as the defect remain in the amorphous phase. The aromatic midchain defect of these two oligomers can be incorporated into the crystalline lamella upon heating below <i>T</i>_m. Then, the adjoining amorphous EO chain crosses from the lamellae to the amorphous regions at an angle ξ, which is preordained by the substitution pattern of the aromatic defect, revealing that the chain tilt angle ranges between 36° ≤ ϕ ≤ 60°

Crystallization of Poly(ethylene oxide) with a Well-Defined Point Defect in the Middle of the Polymer Chain

Poly­(ethylene oxide) (PEO) is a polymer of great interest due to its prevalence in biomedical, pharmaceutical, and ion conductive systems. In this study, the crystallization behaviors of a PEO with 22 monomer units (PEO₂₂) and a PEO having the same degree of polymerization but with an additional 1,4-disubstituted 1,2,3-triazole ring in central position of the chain (PEO₁₁-TR-PEO₁₁) are investigated. PEO₁₁-TR-PEO₁₁ shows one type of lamella crystal after cooling to <i>T</i> = 0 °C, but structural changes during heating below their final melting are detected by WAXS, DSC, POM, and solid-state NMR spectroscopy. The lamella thickness increases, but simultaneously the helix–helix distance decreases and an additional Bragg reflection appears at 2θ = 22.1°. A model is proposed which explains these structural changes by incorporation of the TR ring into the crystals which are additionally stabilized by attractive C–H···π interactions of the TR rings. Additionally, two different types of extended chain lamella crystals are found in PEO₂₂ by SAXS which are discussed in the context of fractionation caused by the molar mass distribution obtained from MALDI-ToF data