11 research outputs found
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 (PEO<sub>22</sub>) 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 (PEO<sub>11</sub>–TR–PEO<sub>11</sub>). In crystals of PEO<sub>22</sub>, the characteristic α<sub><i>c</i></sub>-relaxation (helix jumps) is detected and
the activation energy of this process is calculated from the pure
crystalline <sup>1</sup>H FIDs to 67 kJ/mol. PEO<sub>11</sub>–TR–PEO<sub>11</sub> 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 PEO<sub>11</sub>–TR–PEO<sub>11</sub> is in good agreement with PEO<sub>22</sub> since helical
jump motions could also be detected by analysis of the <sup>1</sup>H FIDs and the corresponding values of their second moments <i>M</i><sub>2</sub>. In contrast, the high temperature phase of
PEO<sub>11</sub>–TR–PEO<sub>11</sub> 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 <sup>1</sup>H time-domain technique and in <sup>13</sup>C MAS CODEX NMR spectroscopy,
i.e. the α<sub><i>c</i></sub>-mobility of PEO in the
HTPh of PEO<sub>11</sub>–TR–PEO<sub>11</sub> is completely
suppressed and the PEO<sub>11</sub> 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 PEO<sub>11</sub>–TR–PEO<sub>11</sub> 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 <sup>13</sup>C 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
(CH<sub>2</sub>)<sub><i>n</i></sub> spacers with 2 ≤ <i>n</i> ≤ 4 (PEO<sub>11</sub>-TR-(CH<sub>2</sub>)<sub><i>n</i></sub>-TR-PEO<sub>11</sub>). The degree of crystallinity
obtained by temperature-dependent WAXS measurements indicates that
only one out of the two PEO<sub>11</sub> chains of the three polymers
forms a 7<sub>2</sub> 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 <sup>13</sup>C 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 PEO<sub>11</sub>-TR-(CH<sub>2</sub>)<sub>2</sub>-TR-PEO<sub>11</sub> 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 PEO<sub>11</sub>-TR-(CH<sub>2</sub>)<sub>4</sub>-TR-PEO<sub>11</sub> after melting of the PEO-TR phase. This
phase has complex characteristics; i.e., the typical 7<sub>2</sub> 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 <sup>13</sup>C MAS NMR spectroscopy. At low temperatures, one
out of the two EO chains of EO<sub>9</sub>-<i>meta</i>-EO<sub>9</sub> and EO<sub>11</sub>-TR-EO<sub>11</sub> 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><sub>m</sub>. 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 (PEO<sub>22</sub>) 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 (PEO<sub>11</sub>-TR-PEO<sub>11</sub>) are investigated.
PEO<sub>11</sub>-TR-PEO<sub>11</sub> 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 PEO<sub>22</sub> by SAXS which are discussed
in the context of fractionation caused by the molar mass distribution
obtained from MALDI-ToF data