Changes in the Electronic Transitions of Polyethylene Glycol upon the Formation of a Coordinate Bond with Li⁺, Studied by ATR Far-Ultraviolet Spectroscopy

This study investigates the electronic transitions of complexes of lithium with polyethylene glycol (PEG) by the absorption bands of solvent molecules via attenuated total reflectance spectroscopy in the far-UV region (ATR–FUV). Alkali-metal complexes are interesting materials because of their functional characteristics such as good ionic conductivity. These complexes are used as polymer electrolytes for Li batteries and as one of the new types of room-temperature ionic liquids, termed solvation ionic liquids. Considering these applications, alkali-metal complexes have been studied mainly for their electrochemical characteristics; there is no fundamental study providing a clear understanding of electronic states in terms of electronic structures for the ground and excitation states near the highest occupied molecular orbital–lowest occupied molecular orbital transitions. This study explores the electronic transitions of ligand molecules in alkali-metal complexes. In the ATR–FUV spectra of the Li–PEG complex, a decrease in intensity and a large blue shift (over 4 nm) were observed to result from an increase in the concentration of Li salts. This observation suggests the formation of a complex, with coordinate bonding between Li+ and the O atoms in PEG. Comparison of the experimental spectrum with a simulated spectrum of the Li–PEG complex calculated by time-dependent density functional theory indicated that changes in the intensities and peak positions of bands at approximately 155 and 177 nm (pure PEG shows bands at 155, 163, and 177 nm) are due to the formation of coordinate bonding between Li+ and the O atoms in the ether molecule. The intensity of the 177 nm band depends on the number of residual free O atoms in the ether, and the peak wavelength at approximately 177 nm changes with the expansion of the electron clouds of PEG. We assign a band in the 145–155 nm region to the alkali-metal complex because we observed a new band at approximately 150 nm in the ATR–FUV spectra of very highly concentrated binary mixtures

Infrared Spectroscopy and X-ray Diffraction Studies of Thermal Behavior and Lamella Structures of Poly(3-hydroxybutyrate-<i>co</i>-3-hydroxyvalerate) (P(HB-<i>co</i>-HV)) with PHB-Type Crystal Structure and PHV-Type Crystal Structure

Thermal behavior and lamella structures of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), hereafter P(HB-co-HV) (HV = 9, 15, 21, 28.8, 58.4, 73.9, and 88.6 mol %), were investigated using infrared (IR) spectroscopy, wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). Temperature-dependent IR and WAXD measurements revealed that P(HB-co-HV) with low HV content (HV = 9, 15, and 21 mol %) has a PHB-type crystal structure with CH3···OC hydrogen bonds, whereas P(HB-co-HV) with high HV content (HV = 73.9 and 88.6 mol %) has a PHV-type crystal structure with CH2···OC hydrogen bonds. The results of IR measurements showed that the strength of the CH3···OC hydrogen bonds in the P(HB-co-HV) (HV = 9, 15, and 21 mol %) copolymers is almost the same as that in PHB, whereas in the P(HB-co-HV) (HV = 28.8 mol %) copolymer, the hydrogen bonds become weaker. In the case of P(HB-co-HV) with higher HV content (HV = 73.9 and 88.6 mol %), the effect of lamella packing on CH2···OC hydrogen bonding in the PHV crystal is not considerable because the side chain of the HB unit is shorter than that of the HV unit. Additionally, it seems that in the crystal structure of P(HB-co-HV) (HV = 58.4 mol %) there are only very weak intermolecular interactions between a CO group and either a CH2 group or a CH3 group because the region of transition of the crystal structure of P(HB-co-HV) from the PHB type to the PHV type occurs at around 50 mol % HV content. Therefore, it is very much possible that with increasing temperature the crystal structure of P(HB-co-HV) (HV = 58.4 mol %) is more likely to collapse than other P(HB-co-HV) copolymers

Effects of Hydrogen Bond Intermolecular Interactions on the Crystal Spherulite of Poly(3-hydroxybutyrate) and Cellulose Acetate Butyrate Blends: Studied by FT-IR and FT-NIR Imaging Spectroscopy

The crystal melting behaviors of poly­(3-hydroxybutyrate) (PHB) and cellulose acetate butyrate (CAB) blends were studied using infrared (IR) and near-infrared (NIR) imaging, which provided information about spherulite growth in dynamic blend systems. By analyzing the changes in the IR and NIR imaging spectra in the regions of the first and second overtones of the CO stretching vibrations of PHB and CAB, the evolution of heterogeneous spherulite during the time-resolved isothermal crystallization process was explored. Time-resolved IR and NIR imaging and polarized microscopic studies detected the PHB domains are able to separate from the PHB/CAB blends early in the process. Principal component analysis (PCA) was used to classify the distribution of the different morphologies of spherulite. The first principal component suggests that the discrimination of the imaging spectra relies largely upon the crystallinity, while the second principal component indicates the variations in the amorphous portion of PHB, the CAB contents, and the intermolecular hydrogen bonding of PHB and CAB. The PC1–PC2 scores of different parts of the spherulite suggest that the areas of low crystallinity in the blend spherulite contain both PHB and CAB

sj-pdf-1-asp-10.1177_00037028221086913 – Supplemental Material for A Study of C=O…HO and OH…OH (Dimer, Trimer, and Oligomer) Hydrogen Bonding in a Poly(4-vinylphenol) 30%/Poly(methyl methacrylate) 70% Blend and its Thermal Behavior Using Near-Infrared Spectroscopy and Infrared Spectroscopy

Supplemental Material, sj-pdf-1-asp-10.1177_00037028221086913 for A Study of C=O…HO and OH…OH (Dimer, Trimer, and Oligomer) Hydrogen Bonding in a Poly(4-vinylphenol) 30%/Poly(methyl methacrylate) 70% Blend and its Thermal Behavior Using Near-Infrared Spectroscopy and Infrared Spectroscopy by Harumi Sato, Yusuke Morisawa, Satoshi Takaya and Yukihiro Ozaki in Applied Spectroscopy</p

Thermally Induced Exchanges of Hydrogen Bonding Interactions and Their Effects on Phase Structures of Poly(3-hydroxybutyrate) and Poly(4-vinylphenol) Blends

Effects of various hydrogen bondings (HBs) and thermally induced exchanges of them on cold crystallization and melting of poly(3-hydroxybutyrate) (PHB) and poly(4-vinylphenol) (PVPh) blends were explored as a function of the PVPh weight fraction (wPVPh) by using Fourier transform infrared spectroscopy. The HBs investigated in this work include intramolecular HBs within PHB crystals (intra PHB) as observed in the CO and CH stretching band regions, intramolecular HBs within PVPh (intra PVPh) as observed in the OH stretching band region, and intermolecular HBs (inter) between the CO groups of PHB in amorphous phase and the OH groups of PVPh. The results elucidated the following pieces of evidence. (i) Inter and intra PVPh suppress the rate of the crystallization and hence the crystallinity of PHB crystals in the blend via formation of physical cross-links in PHB and PVPh chains in the amorphous phase or melt. The crystallization and melting occur in two steps: (ii) the crystallization involves the dissociation of inter and intra PVPh, followed by the association of intra PHB and the reassociation of intra PVPh; (iii) the melting involves the dissociation of intra PHB, followed by the association of inter. (iv) Among CO groups of PHB in the melt blends existing in either free CO or inter, the fraction of inter linearly increases with wPVPh, which in turn suppresses the PHB crystallinity under given crystallization conditions to a greater extent due to an increased number of physical cross-links and hence due to the suppressed crystallization rate

Quantum Mechanical Interpretation of Intermolecular Vibrational Modes of Crystalline Poly‑(<i>R</i>)‑3-Hydroxybutyrate Observed in Low-Frequency Raman and Terahertz Spectra

Low-frequency vibrational bands observed in the Raman and terahertz (THz) spectra in the region of 50–150 cm–1 of crystalline powder poly-(R)-3-hydroxybutyrate (PHB) were assigned based on comparisons of the Raman and THz spectra, polarization directions of THz absorption spectra, and their congruities to quantum mechanically (QM) calculated spectra. This combination, Raman and THz spectroscopies and the QM simulations, has been rarely adopted in spite of its potential of reliable assignments of the vibrational bands. The QM simulation of a spectrum has already been popular in vibrational spectroscopies, but for low-frequency bands of polymers it is still a difficult task due to its large scales of systems and a fact that interactions among polymer chains should be considered in the calculation. In this study, the spectral calculations with the aid of the Cartesian-coordinate tensor transfer (CCT) method were applied successfully to the crystalline PHB, which include the explicit consideration of an intermolecular interaction among helical polymer chains. The agreements between the calculations and the experiments are good in both the Raman and THz spectra in terms of spectral shapes, frequencies, and intensities. A Raman active band at 79 cm–1 was assigned to the intermolecular vibrational mode of the out-of-plane CO + CH3 vibration. A polarization state of the corresponding far-infrared absorption band at ∼82 cm–1, perpendicular to the helix-elongation direction of PHB, was reproduced only under the explicit correction, which indicates that this polarized band originates from the interaction among the polymer chains. The calculation explored that the polarization direction of this band was along the a axis, which is consistent with the direction in which weak intermolecular hydrogen bonds are suggested between the CO and CH3 groups of two parallel polymer chains. The results obtained here have confirmed sensitivity of the low-frequency vibrational bands to the weak hydrogen bonds among the polymer chains

Low-Frequency Vibrational Modes of Poly(glycolic acid) and Thermal Expansion of Crystal Lattice Assigned On the Basis of DFT-Spectral Simulation Aided with a Fragment Method

Low-frequency vibrational modes of lamellar crystalline poly­(glycolic acid) (PGA) were measured on Raman and far-infrared (FIR) spectra. Among the observed bands, an FIR band at ∼70 cm–1 and a Raman band at 125 cm–1 showed a gradual lower-frequency shift with increasing temperature from 20 °C to the melting point at ∼230 °C. Their polarization direction was perpendicular to the chain axis of PGA. Both spectra were quantum-mechanically simulated with the aid of a fragment method, the Cartesian-coordinate tensor transfer, which enabled an explicit consideration of molecular interactions between two adjacent polymer chains. Good agreement was achieved between the experiment and theory in both spectra. The temperature-sensitive bands at ∼70 cm–1 in FIR and at 125 cm–1 in Raman comprise the out-of-plane CO bending motion. The temperature-dependent shifts of the low-frequency bands were successfully simulated by the DFT-spectral calculation, exploring that the main origin of the shifts is the thermal expansion of the crystal lattice. This result indicates that the thermally shifted bands may be used as an indicator of the lattice expansion of PGA. Possible changes in intermolecular interactions of PGA under temperature rising were ascribed on the basis of natural bond orbital theory. The steric repulsion between the carbonyl O atom in one chain and the H–C bond in the adjacent chain will be a dominant interaction in the lattice-expanding process, which would cause the observed thermal shifts of the bending modes. Comparisons of the spectral assignment for PGA obtained in this study and that for poly-(R)-3-hydroxybutyrate (PHB) reported by us suggest that crystalline polyesters give vibrational modes composed of out-of-plane bending motion of CO groups between ∼70 and ∼125 cm–1, the modes of which are sensitive to the thermal expansion of crystal lattice and its concomitant changes in their intermolecular interactions

Rydberg and π–π* Transitions in Film Surfaces of Various Kinds of Nylons Studied by Attenuated Total Reflection Far-Ultraviolet Spectroscopy and Quantum Chemical Calculations: Peak Shifts in the Spectra and Their Relation to Nylon Structure and Hydrogen Bondings

Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 145–260 nm region were measured for surfaces (thickness 50–200 nm) of various kinds of nylons in cast films to explore their electronic transitions in the FUV region. ATR-FUV spectra show two major bands near 150 and 200 nm in the surface condensed phase of nylons. Transmittance (Tr) spectra were also observed in particular for the analysis of valence excitations. Time-dependent density functional theory (TD-DFT/CAM-B3LYP) calculations were carried out using the model systems to provide the definitive assignments of their absorption spectra and to elucidate their peak shifts in several nylons, in particular, focusing on their crystal alignment structures and intermolecular hydrogen bondings. Two major bands of nylon films near 150 and 200 nm are characterized as σ-Rydberg 3p and π–π* transitions of nylons, respectively. These assignments are also coherent with those of liquid <i>n</i>-alkanes (<i>n</i> = 5–14) and liquid amides observed previously. The Rydberg transitions are delocalized over the hydrocarbon chains, while the π–π* transitions are relatively localized at the amide group. Differences in the peak positions and intensity were found in both ATR- and Tr-FUV spectra for different nylons. A red-shift of the π–π* amide band in the FUV spectra of nylon-6 and nylon-6/6 models in α-form is attributed to the crystal structure pattern and the intermolecular hydrogen bondings, which result in the different delocalization character of the π–π* transitions and transition dipole coupling

Combined X‑ray Reflectivity and Infrared Study of the Effect of Hydrogen Bonding of the OH Group on the Relaxation Behavior in Ultrathin Polyvinylphenol Films on SiO₂

Utilizing X-ray reflectivity and infrared reflection absorption spectroscopy (IR-RAS), we have investigated the thermal expansion and contraction of ultrathin polyvinylphenol (PVPh) films supported on a silicon (100) substrate capped with an amorphous SiO2 layer. Despite being known to form strong interactions with the SiO2 surface, the thin PVPh films showed a reduction in the glass-transition point Tg, similar to the behavior of polystyrene thin films deposited on SiO2. We explored the relationship between thermal expansivity and film thickness using well-annealed films and found that it decreases with film thickness in the range below twice the radius of gyration of a polymer chain (2Rg) in the glassy state. Thickness expansion in the glassy state and contraction in thickness at temperatures higher than Tg bulk (melt state) showed the presence of two competing relaxation processes. The reported negative thermal expansion in PVPh thin films, which was discovered to be one of the inherent properties, may have been caused by the fast relaxations that take place at the free polymer surface. IR-RAS was utilized to investigate the effect of thickness on hydrogen bonding in PVPh, and it was confirmed that with decreasing thickness, hydrogen bonding becomes weak, and the number of free OH groups increases. Therefore, thinner PVPh samples exhibit lower Tgs as an effect of easier molecular motions