Hydrogen Bonds In Poly Research Articles

An Extremely Stretchable and Self-Healable Supramolecular Polymer Network.

The construction of a single polymer network with extreme stretchability, relatively high mechanical strength, and fast and facile autonomous room-temperature self-healing capability still remains a challenge. Herein, supramolecular polymer networks are fabricated by synergistically incorporating metal-ligand and hydrogen bonds in poly(propylene glycol) (PPG). The representative specimen, PPG-Im-MDA-1.5-0.25-Cu, shows a combination of notable mechanical properties involving an extreme stretching ratio of 346 ± 14× and a Young's modulus of 2.10 ± 0.14 MPa, which are superior to the previously reported extremely stretchable polymeric materials. Notably, the destroyed specimen can fully recover mechanical performances within 1 h. The tunability of mechanical properties and self-healing capability has been actualized by merely tailoring the content of a chain extender. The application of the as-prepared supramolecular PPG network in constructing a flexible and self-healable conductor has been demonstrated. This strategy provides some insights for preparing extremely stretchable and self-healable polymeric materials.

Thermocontrol of solute permeation across polymer membrane composed of poly(N,N-dimethylaminoethyl methacrylate) and its copolymers

Polymer membranes composed ofN,N-dimethylaminoethyl methacrylate (DMAEMA) and acrylamide (AAm) (or ethyl acrylamide (EAAm)) were prepared to demonstrate the thermocontrol of solute permeation. Poly DMEMA has a lower critical solution temperature (LCST) at around 50°C in water. With the copolymerization of DMAEMA with AAm (or EAAm), a shift in the LCST to a lower temperature was observed, probably due to the formation of hydrogen bonds between the amide andN,N-dimethylamino groups. However, the temperature-induced phase transition of poly (DMAEMA-co-EAAm) did not show a similar trend to that of poly (DMAEMA-co-AAm) in the gel state. The hydrogen bonds in poly (DMAEMA-co-EAAm) were significantly disrupted with the formation of a gel network, which led to a difference in the swelling behavior of polymer gels in response to temperature. To apply these polymers to temperature-sensitive solute permeation, polymer membranes were prepared. The permeation pattern of hydrocortisone, used as the model solute, was explained based on the temperature-sensitive swelling behavior of the polymer membranes.

Studies on Different Types of Hydrogen Bonds in Poly(vinyl alcohol) Films by 1H CRAMPS and Solid-State Two-Dimensional 1H-13C Heteronuclear Correlation Analyses

Different hydrogen-bonded states of OH groups in poly(vinyl alcohol) (PVA) films with different tacticities have been characterized by 1H combined rotation and multiple pulse spectroscopy (CRAMPS), solid-state 13C NMR and two-dimensional (2D) 1H-13C heteronuclear correlation (HETCOR) analyses. The newly developed line shape analysis for the 1H CRAMPS spectra reveals the existence of three types of OH groups in different hydrogen-bonded states below Tg; intramolecular and intermolecular hydrogen bonded OH (OHintra, OHinter) groups and OH (OHf) groups free from hydrogen bonding. Above Tg, another resonance line which can be assigned to highly mobile OH (OHr) groups in the noncrystalline region appears as a result of the reduction in mole fractions of the OHintra and OHinter groups, in good accord with the confirmation of the rubbery component by the solid-state 13C NMR line shape analysis. In contrast, the mole fraction of the OHf groups stays constant at −60-160°C, indicating that these OH groups are preferentially distributed in the crystalline region. In order to examine the correlations of the results obtained by 1H CRAMPS and solid-state 13C NMR analyses, 2D 1H-13C HETCOR spectra have been also measured at room temperature for atactic and main-chain deuterated atactic PVA films. As a result, evident correlations between 1H OH and 13C CH constituent lines are observed at a cross polarization (CP) contact time of 120 μs, indicating the validity of the assignments for the 1H OH and 13C CH resonance lines made previously as well as in this work.

Hydrogen bonds in poly(methyl methacrylate)-poly(4-vinyl phenol) blends: 2. Quantification near the glass transition temperature

Changes in the proportion of hydrogen bonds of poly(4-vinyl phenol) (PVPh) and poly(methyl methacrylate) (PMMA) blends have been investigated by FTi.r. spectroscopy both above and below the glass transition temperature T g. Changes in three spectral regions, namely the carbonyl, hydroxyl and aromatic ring vibration regions, are attributed to variations in hydrogen bonding with increasing temperature. Both hydrogen bonded OH and CO stretching vibrations shift to higher frequencies, indicating a weakening of interassociated hydrogen bonds at higher temperatures. A clear transition is observed in the absorbance behaviour of these vibrations at T g. The reduction in total area of OH and CO vibration regions is attributed not only to the breaking of hydrogen bonds at T g, but also to the decrease of absorption coefficients of hydrogen bonded OH and CO stretching vibrations. Quantification of the decrease in concentration ratio of hydrogen bonds between carbonyl groups vs. total carbonyl groups showed a decrease of 0.5% in the number of hydrogen bonds was occuring at T g + 30, when T g is taken as the midpoint of the transition as determined by DSC, for the 30 wt% PVPh composition. For higher compositions, this percentage increased, reaching 3.5% for the 80 wt% PVPh composition, which is related to the increase in T g of the blend.

Hydrogen bonds in poly(methyl methacrylate)-poly(4-vinyl phenol) blends: 1. Quantitative analysis using FTi.r. spectroscopy

FTi.r. was used to investigate quantitatively hydrogen bonds in poly(methyl methacrylate) (PMMA) and poly(4-vinyl phenol) (PVPh) blends. An absorption coefficient of free (or non-hydrogen bonded) carbonyl vibration of 750 ± 40 cm −1 m 2 mol −1 was determined from pure PMMA using the Beer-Lambert law, along with precise measurements of film thickness and density. By making the approximation that this value is the same for pure PMMA and for PMMA in blends, the absorption coefficient of the hydrogen bonded carbonyl vibration was calculated as 910 ± 50 cm −1m 2 mol −1. Using these values, it was deduced that less than 45% of carbonyl groups are involved simultaneously in hydrogen bonding for a blend where the PVPh to PMMA mole ratio was 1 to 1. In pure PVPh, OH groups exist as n-mers, with a predominance of shorter mers such as trimers or tetramers. Upon addition of PMMA to PVPh, the fraction of intra-associated OH bonds remains, within experimental error, constant whereas inter hydrogen bonds between PVPh and PMMA chains increase, resulting in a decrease in free OH groups. Above 45.5 wt% PMMA, almost all ‘free’ OH groups have disappeared, and intra- and inter-associated hydrogen bonds are distributed among the available OH groups. Finally, at high PMMA content (90 wt% PMMA, or 10 wt% PVPh), the probability of two PVPh chains to be close enough to allow intra-hydrogen bond formation is small, and only inter-hydrogen bonds between PVPh and PMMA are observed.

Proton transfer involving nucleic acids: A temperature-jump study of the systems sulphonephthaleins-double stranded poly(A) and sulphonephthaleins-double stranded poly(C)

The kinetics of proton transfer between poly(A—AH) (partially protonated double-stranded polyadenylic acid) and CPR (chlorophenol red), and between poly(C—H—C) (partially protonated double-stranded polycytidylic acid) and the indicators CPR, BCP (bromocresol purple), and BCG (bromocresol green) have been investigated at 25°C and ionic strength 0.1 M (NaClO4) by the temperature-jump method. The acidic proton of poly(C—H—C) is engaged in a hydrogen bond (N3H+––––N3) which is believed to contribute to stabilizing the double-strand conformation, whereas the acidic proton of poly(A—A—H) does not form hydrogen bonds. The analysis of the dependence of the relaxation times on the concentrations of the reactants has enabled the evaluation of the rate constants for the direct proton transfer and for the protolysis paths. The rate constants for proton recombination with the deprotonated forms of the polynucleotides and the indicators are of the order of magnitude expected for diffusion controlled processes involving oppositely charged ions (k2=(0.2−1.6)×1010 M−1s−1). The direct proton transfer from poly(C—H—C) to BCG is thermodynamically disfavored and its rate constant, k1, is lower than k2 by about three orders of magnitude. The (thermodynamically favored) proton transfers from poly(A—A—H) to CPR and from poly(C—H—C) to CPR and BCP are characterized by similar values of k1. This result indicates that the hydrogen bonds in poly(C—H—C) are very weak and suggests that the stabilization of the double-stranded conformation of this polynucleotide could be ascribed to the large number of hydrogen bonds rather than to their specific strength. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 161–169, 1998.

Hydrogen bonds in poly(ester amide)s and their model compounds

The hydrogen bonds in poly(ester amide)s and their model compounds were investigated using infra-red spectroscopy in the temperature range from 20 to 240°C. It was found that in the polymers investigated both amide—amide and amide—ester hydrogen bonds were formed, while in the corresponding model compounds only amide-amide hydrogen bond formation was observed.