DFT, ab initio, NMR, and NBO analyses of N-substituted hydrazino acetamides: Experimental vs theoretical values

We studied the DFT (B3LYP) and HF at 6-31+G/6-31+G^∗∗ levels of theory in order to throw light on the conformation, structure, intramolecular hydrogen bond network, as well as proton and nitrogen NMR (GIAO method) of a series of model primary amides in the gas phase and/or in solution (chloroform, methanol, water, dimethyl sulfoxide, and heptane). In this manner, it was possible to show that the amidic group of these model compounds acts as the H-bond donor and interacts with two different H-bond acceptors, thus stabilizing the C₈ pseudocycle. The study was conducted to gain a better understanding of the conformation (both experimentally and theoretically) adopted by hydrazino acetamides (model compounds for aza-β³-peptides). In the light of this, we were able to explain why aza-β³-peptides develop a different H-bond network in comparison to their isosteric β³-peptide analogues (an extension of the β-peptide concept).     

Diverse Coordination Geometries Derived from Trisaminocyclohexane Ligands with Appended Outer-Sphere Hydrogen Bond Donors

With the aim of constructing hydrogen-bonding networks in synthetic complexes, two new ligands derived from cis,cis-1,3,5-triaminocyclohexane (TACH) have been prepared that feature pendant pyrrole or indole rings as outer-sphere H-bond donors. The TACH framework offers a facial arrangement of three N-donors, thereby mimicking common coordination motifs in the active sites of nonheme Fe and Cu enzymes. X-ray structural characterization of a series of Cu^I-X complexes (X=F, Cl, Br, NCS) revealed that these neutral ligands (H₃L^R, R=pyrrole or indole) coordinate in the intended facial N₃ manner, yielding four-coordinate complexes with idealized C₃ symmetry. The N−H units of the outer-sphere heterocycles form a hydrogen-bonding cavity around the axial (pseudo)halide ligand, as verified by crystallographic, spectroscopic, and computational analyses. Treatment of H₃L^pyrrole and H₃L^indole with divalent transition metal chlorides (M^IICl₂, M=Fe, Cu, Zn) causes one heterocycle to deprotonate and coordinate to the M(II) center, giving rise to tetradentate ligands with two remaining outer-sphere H-bond donors. Further ligand deprotonation is observed upon reaction with Ni(II) and Cu(II) salts with weakly coordinating counteranions. The reported complexes highlight the versatility of TACH-based ligands with pendant H-bond donors, as the resulting scaffolds can support multiple protonation states, coordination geometries, and H-bonding interactions.     

DFT and ab initio potential energy scan and hydrogen bond analysis of N-substituted hydrazino acetamides: Characterization of the “hydrazinoturn” hydrogen bonding pattern

We studied a series of model primary amides in gas phase at the DFT (B3LYP) and HF at 6-31+G/6-31+G** levels of theory in order to shed light on their conformation, structure, and intramolecular hydrogen bonding network. A potential energy scan was performed by rotating around the appropriate bond for each molecule studied in this paper. In this manner, it was possible to show that the amidic group of these model compounds acts as H-bond donor and interacts with two different H-bond acceptors which stabilizes a C₈ pseudocycle, the so called “hydrazinoturn”. This study was addressed theoretically in order to understand the conformation adopted by hydrazino acetamides as model compounds for aza-β³-peptides. We thus investigated the conformational analysis of hydrazinoturns computationally and showed that these systems represent a very stabilizing folding driving force, provided that the neighboring molecular functional groups do not imply other competing hydrogen bonding patterns.     

Cooperative interactions of hydrogen bonds in proton-transfer processes involving water molecules. Simulation of biochemical systems

Quantum-chemical calculations of molecular complexes simulating the proton channel of influenza A virus and the proton-transfer system of the active site of carboanhydrase enzyme were performed. These complexes comprise a proton-donor and a proton-acceptor groups bridged by a chain of water molecules. Calculations of the methylimidazole (H⁺)-H₂O-CH₃COO^? complex as a model of influenza M₂ virus revealed free translation motion of the water molecule between the donor and acceptor, as well as concerted proton transfer in both H bonds. The barrier for proton transfer is independent of the position of the bridging water molecule and varies linearly with the difference in the electrostatic potentials between the donor and acceptor. With elongation of the H-bond bridge between the donor and acceptor groups, the H-bond lengths and proton shifts in the chain links vary periodically. This process can be defined as an H-bond deformation wave (proton wave). It was shown that motion of one proton along the H bond is associated with vibrational motion of protons in other links, which results in wave propagation along the chain. The calculation results allowed the rate of the proton wave and the time of proton transfer from the donor to acceptor to be estimated.     

H-Bonded metallomesogens: preparation, characterization, and mesomorphic studies of (3-hydroxypropylimino)propan-1,2-diols

Two series of new Schiff bases 2 (n=8, 12, 16) derived from (3-hydroxypropyl imino)propan-1, 2-diol with a hydroxyl group at C₁₉/C₂₀-position and their palladium complexes 1 were prepared and their mesomorphic properties investigated by DSC, POM, and XRD. The presence of both hydroxyl groups was found to be crucial in forming the liquid crystalline behavior. All compounds 2a exhibited smectic A or and C phases, in contrast, all compounds 2b formed hexagonal columnar phases. The formation of mesophases in both compounds 1-2 was probably induced by inter-molecular H-bonds. Single crystallographic data in mesogenic compound 2a (n=8) indicated that a dimeric structure with a better linear or rod-like molecular shape was formed by an inter-molecular H-bond (O4-O1′, ∼1.854 Å). Another inter-molecular H-bond (∼1.903 Å) between two dimeric structures was also observed. It crystallizes in a monoclinic space group P2(1)/c. On the other hand, all palladium complexes 1 formed enantiotropic smectic A phases. Single crystallographic data in mesogenic compound 1a (n=8) indicated that the geometry at Pd²⁺ center was coordinated as slightly twisted square planar. It crystallizes in a monoclinic space group P2(1)/n. An inter-molecular H-bond (∼1.799 Å) between neighboring molecules were observed, which might have facilitated the formation of mesophases. Variable-temperature powder XRD experiments confirmed their mesophase structures.     

Hydrogen bonding interactions between <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylformamide and cysteine: DFT studies of structures,properties, and topologies

The hydrogen bonding interactions between cysteine and N,N-dimethylformamide (DMF) were studied at the extended hybrid functional DFT-X3LYP/6-311++G(d,p) level regarding their geometries, energies, vibrational frequencies, and topological features of the electron density. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses were employed to elucidate the interaction characteristics in the complexes. The results show that two intermolecular hydrogen bonds (H-bonds) are formed in one complex except few complexes with one intermolecular H-bond. The H-bonds involving O atom of DMF as H-bond acceptor usually are red-shifting H-bonds, while the blue-shifting H-bond usually involve methyl of DMF or methenyl of cysteine moiety as H-bond donors. Both hydrogen bonding interaction and structural deformation play important roles in the relative stabilities of the complexes. Due to the π-bond cooperativity, the strongest H-bond is formed between hydroxyl of cysteine moiety and O atom of DMF, however, the serious deformation counteract the hydrogen bonding interaction to a great extent. The complex involves a stronger hydrogen bonding interaction as well as the smaller deformation is the most stable one. The electron density (ρ_b) as well as its Laplacian (∇²ρ_b) at the H-bond critical point predicted by QTAIM is strongly correlated with the H-bond structural parameter (δR _H···Y) and the second-perturbation energies E(2) in the NBO scheme.     

Density functional theory and topological analysis on the hydrogen bonding interactions in N-protonated adrenaline–DMSO complexes

In this study, complexes formed via hydrogen bond interactions between N-protonated adrenaline (AdH⁺) and DMSO have been studied by density functional theory (DFT). The relevant geometries, energies, and IR characteristics of the hydrogen bonds (H-bonds) have been systematically investigated. The natural bond orbital (NBO) and the quantum theory of atoms in molecule (QTAIM) analysis have also been applied to understand the nature of the hydrogen bonding interactions in complexes. The H-bonds involving amino or hydroxyls as H-donor are dominant H-bonds in complexes and are attributed to strong H-bonds. The weak H-bonds, such as π H-bonds and H-bonds involving methyl (DMSO) or methenyls (C2H6 and C5H7 of AdH⁺) as H-acceptors, were found in complexes as well. The complexes in which the dominant H-bond involves amino of AdH⁺ as H-donor are more stable than those with the dominant H-bond involving hydroxyls as H-donor. Some relationships between various properties of QTAIM, NBO, geometry as well as frequency were also investigated.     

Silver-Free Au(I) Catalysis Enabled by Bifunctional Urea- and Squaramide-Phosphine Ligands via H-Bonding

A library of gold(I) chloride complexes with phosphine ligands incorporating pendant (thio)urea and squaramide H-bond donors was prepared with the aim of promoting chloride abstraction from Au(I) via H-bonding. In the absence of silver additives, complexes bearing squaramides and trifluoromethylated aromatic ureas displayed good catalytic activity in the cyclization of N-propargyl benzamides, as well as in a 1,6-enyne cycloisomerization, a tandem cyclization-indole addition reaction and the hydrohydrazination of phenylacetylene. Kinetic studies and DFT calculations indicate that the energetic span of the reaction is accounted by both the chloride abstraction step, facilitated by the bidentate H-bond donor via an associative mechanism, and the subsequent cyclization step.     

Trimethylglycine complexes with carboxylic acids and HF: solvation by a polar aprotic solvent

A series of strong H-bonded complexes of trimethylglycine, also known as betaine, with acetic, chloroacetic, dichloroacetic, trifluoroacetic and hydrofluoric acids as well as the homo-conjugated cation of betaine with trifluoroacetate as the counteranion were investigated by low-temperature (120-160 K) liquid-state NMR spectroscopy using CDF(3)/CDF(2)Cl mixture as the solvent. The temperature dependencies of (1)H NMR chemical shifts are analyzed in terms of the solvent-solute interactions. The experimental data are explained assuming the combined action of two main effects. Firstly, the solvent ordering around the negatively charged OHX region of the complex (X = O, F) at low temperatures, which leads to a contraction and symmetrisation of the H-bond; this effect dominates for the homo-conjugated cation of betaine. Secondly, at low temperatures structures with a larger dipole moment are preferentially stabilized, an effect which dominates for the neutral betaine-acid complexes. The way this second contribution affects the H-bond geometry seems to depend on the proton position. For the Be(+)COO(-)···HOOCCH(3) complex (Be = (CH(3))(3)NCH(2)-) the proton displaces towards the hydrogen bond center (H-bond symmetrisation, O···O contraction). In contrast, for the Be(+)COOH···(-)OOCCF(3) complex the proton shifts further away from the center, closer to the betaine moiety (H-bond asymmetrisation, O···O elongation). Hydrogen bond geometries and their changes upon lowering the temperature were estimated using previously published H-bond correlations.     

Synthesis,characterization, molecular and supramolecular structures of nickel(II) complexes derived from α-diketone and α-ketoaldehyde bisaroylhydrazones

A new series of nickel(II) complexes derived from symmetrical diacetyl bisaroylhydrazones [Ni(L¹-R)] and unsymmetric phenylglyoxal bisaroylhydrazones [Ni(L²-R)] have been prepared and characterized. X-ray crystal and molecular structures of [Ni(L¹-H)], [Ni(L¹-pCH₃O)] and [Ni(L¹-pNO₂)] have been determined. In these complexes, the Ni(II) is in a distorted square planar environment and the aroylhydrazone acts as dinegative tetradentate ligand forming a 5,5,5-tricyclic chelate ring. Reaction of [Ni(L¹-R)] with aqueous ammonia afforded the paramagnetic five coordinate [Ni(L¹-R)(NH₃)] while [Ni(L²-R)] gave the diamagnetic square planar [Ni(L²-R)(NH₃)] complexes. Reaction of [Ni(L¹-R)] complexes with imidazole gave the corresponding paramagnetic octahedral bis(imidazole) adducts. X-ray structures of both [Ni(L¹-H)(HIm)₂] and [Ni(L¹-pNO₂)(HIm)₂] suggest a distorted octahedral structure where the bisaroylhydrazone occupies the basal plane while the two imidazoles occupy the axial sites. The molecular units are associated together forming triple stranded helical chains. With imidazole the [Ni(L²-R)] series gave the corresponding diamagnetic mono(imidazole) [Ni(L²-R)(HIm)] complexes, The X-ray structure of {Ni(L²-pCH₃)(HIm)] suggest square planar arrangement around the Ni(II) where the bisaroylhydrazone acts as dinegative NNO tridentate ligand forming with the Ni(II) a 5,6-bicyclic chelate ring the fourth coordination site is occupied by imidazole nitrogen.     

The Role of Ligand Topology in the Decomplexation of Luminescent Lanthanide Complexes by Dipicolinic Acid

In this study, we present the aqueous solution behavior of two luminescent lanthanide antenna complexes (Eu³⁺? 1 , Dy³⁺? 9 ) with different ligand topologies in the presence of dipicolinic acid (DPA, pyridine‐2,6‐dicarboxylic acid). Macrocyclic (1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid, DO3A, 9 ) and acyclic (1,4,7‐triazaheptane‐1,1,7,7‐tetraacetic acid, DTTA, 1 ) ligands have been selected to form a ratiometric pair in which Dy³⁺? 9 acts as a reference and Eu³⁺? 1 acts as a probe for the recognition of DPA. The pair of luminescent complexes in water reveals the capability to work as a DPA luminescent sensor. The change of emission intensity of Eu³⁺ indicates the occurrence of a new sensitization path for the lanthanide cation through excitation of DPA. NMR evidence implies the presence of free 1 and mass spectrometry shows the formation of emitting [EuDPA₂]^? as a result of a ligand exchange reaction.     

Polymer complexes. LXVII: electrical conductivity and thermal properties of polymer complexes of quinoline azo dye

A novel series of divalent transition metals (Cu²⁺, Co²⁺ and Ni²⁺) polymer complexes of azo ligand named 5-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-8-hydroxyquinoline (Q) have been synthesized. The azo quinoline ligand (Q) and polymer complexes are characterized by various physicochemical techniques. The thermal properties of the ligand and its isolated polymer complexes are studied using thermogravimetric analysis. The physicochemical investigations elucidate that the azo ligand acts as a neutral bis(bidentate) ligand. The polymer complexes are found to be octahedral geometry. The change in the ac electrical conductivity, loss tangent and dielectric properties are studied upon heating in temperature region 298–550 K and frequency ranging from 0.1 to 100 kHz, moreover, the mechanism of conduction is determined. The electrical conductivity studies indicate that the ligand (Q) and polymer complexes have the semiconducting behavior. The correlated barrier hopping is the dominant conduction mechanism for all samples.     

Oxorhenium(V) complexes with tetradentate NSNO pyridylthioazophenolates: syntheses, spectral and electrochemical studies

A family of oxorhenium(V) complexes of newly designed pyridylthioazophenolate ligands has been synthesized and isolated in pure form. The solid state structure of an organic compound (HL1) has been established by X-ray crystallography. The molecular structure observed in the solid state is that the two molecules of the ligand (HL1) in the asymmetric unit have similar geometries, except for the orientation of the pyridine ring. This series of organic moieties acts as tetradentate monobasic NSNO donor chelators in oxorhenium(V) complexes which has been characterized by elemental analyses, IR, ¹H-NMR, UV–Vis. The complexes are 1:1 electrolytes in nature in MeOH solution, the counter anion being ClO ₄ ⁻ . The electrochemical studies of the [Re^VO(L)Cl]ClO₄ complexes in MeCN using TBAP as supporting electrolyte exhibit quasi-reversible voltammogram showing one-electron couple for [Re^VIO(L)Cl]²⁺−[Re^VO(L)Cl]⁺ in the 1.11–1.29 V vs SCE range.     

A modular approach toward regulating the secondary coordination sphere of metal ions: differential dioxygen activation assisted by intramolecular hydrogen bonds

Metal ion function depends on the regulation of properties within the primary and second coordination spheres. An approach toward studying the structure-function relationships within the secondary coordination sphere is to construct a series of synthetic complexes having constant primary spheres but structurally tunable secondary spheres. This was accomplished through the development of hybrid urea-carboxamide ligands that provide varying intramolecular hydrogen bond (H-bond) networks proximal to a metal center. Convergent syntheses prepared ligands [(N'-tert-butylureayl)-N-ethyl]-bis(N' '-R-carbamoylmethyl)amine (H(4)1R) and bis[(N'-tert-butylureayl)-N-ethyl]-(N' '-R-carbamoylmethyl)amine (H(5)2R), where R=isopropyl, cyclopentyl, and (S)-(-)-alpha-methylbenzyl. The ligands with isopropyl groups H(4)1iPr and H(5)2iPr were combined with tris[(N'-tert-butylureayl)-N-ethyl]amine (H6buea) and bis(N-isopropylcarbamoylmethyl)amine (H(3)0iPr) to prepare a series of Co(II) complexes with varying H-bond donors. [CoIIH(2)2iPr]- (two H-bond donors), [CoIIH1iPr]- (one H-bond donor), and [CoII0iPr]- (no H-bond donors) have trigonal monopyramidal primary coordination spheres as determined by X-ray diffraction methods. In addition, these complexes have nearly identical optical and EPR properties that are consistent with S=3/2 ground states. Electrochemical studies show a linear spread of 0.23 V in anodic potentials (Epa) with [CoIIH(2)2iPr]- being the most negative at -0.385 V vs [Cp2Fe]+/[Cp2Fe]. The properties of [CoIIH3buea]- (H3buea, tris[(N'-tert-butylureaylato)-N-ethyl]aminato that has three H-bond donors) appears to be similar to that of the other complexes based on spectroscopic data. [CoIIH3buea]- and [CoIIH(2)2iPr]- react with 0.5 equiv of dioxygen to afford [CoIIIH3buea(OH)]- and [CoIIIH(2)2iPr(OH)]-. Isotopic labeling studies confirm that dioxygen is the source of the oxygen atom in the hydroxo ligands: [CoIIIH3buea(16OH)]- has a -(O-H) band at 3589 cm-1 that shifts to 3579 cm-1 in [CoIIIH3buea(18OH)]-; [CoIIIH(2)2iPr(OH)]- has -(16O-H)=3661 and -(18O-H)=3650 cm-1. [CoIIH1iPr]- does not react with 0.5 equiv of O2; however, treating [CoIIH1iPr]- with excess dioxygen initially produces a species with an X-band EPR signal at g=2.0 that is assigned to a Co-O2 adduct, which is not stable and converts to a species having properties similar to those of the CoIII-OH complexes. Isolation of this hydroxo complex in pure form was complicated by its instability in solution (kint=2.5x10-7 M min-1). Moreover, the stability of the CoIII-OH complexes is correlated with the number of H-bond donors within the secondary coordination sphere; [CoIIIH3buea(OH)]- is stable in solution for days, whereas [CoIIIH(2)2iPr(OH)]- decays with a kint=5.9x10-8 M min-1. The system without any intramolecular H-bond donors [CoII0iPr]- does not react with dioxygen, even when O2 is in excess. These findings indicate a correlation between dioxygen binding/activation and the number of H-bond donors within the secondary coordination sphere of the cobalt complexes. Moreover, the properties of the secondary coordination sphere affect the stability of the CoIII-OH complexes with [CoIIIH3buea(OH)]- being the most stable. We suggest that the greater number of intramolecular H-bonds involving the hydroxo ligand reduces the nucleophilicity of the CoIII-OH unit and reinforces the cavity structure, producing a more constrained microenvironment around the cobalt ion.     

Neutral Hexacoordinate Tin(IV) Halide Complexes with 4,4'-Dimethy-2,2'-bipyridine

A series of three neutral, hexacoordinate tin(IV) complexes were synthesized by the reaction of 4,4'-dimethyl-2,2'-bipyridine (DMB) with SnX₄, X = Cl, Br, and I, as starting materials. The complexes (DMB)SnX₄ were characterized in solution by ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy, and in the solid-state by ¹¹⁹Sn MAS NMR spectroscopy. In addition, single-crystal X-ray diffraction and elemental analysis were used to confirm the molecular structures. In these complexes, the tin atom adopts a distorted octahedral arrangement and the DMB acts as a bidentate N,N'-chelate ligand. Computational DFT methods were also employed to gain more insight into the nature of the bonding in these complexes, including the hypothetical complexes (DMB)SnX₄ (X = F, At). Additionally, the validity and reliability of the ¹¹⁹Sn NMR chemical shifts were examined. The calculated values were compared with the experimental signals and the effects of structure and solvent are discussed. Finally, all of the complexes (DMB)SnX₄ were successfully tested for the ring-opening polymerization (ROP) of bulk ε-caprolactone under non-dried and aerobic conditions as precatalyst.     

Conformations of 2-phenylethanol and its singly hydrated complexes: UV–UV and IR–UV ion-dip spectroscopy

The structures of 2-phenylethanol and its 1:1 water complexes have been investigated by UV–UV holeburning and IR–UV ion-dip spectroscopy, coupled with ab initio computation. The most populated molecular conformer is stabilized by an intramolecular π-type H-bond and its rotational band contours suggest the incidence of vibronic coupling involving motion of the side chain. Its 1:1 water complexes are associated with two distinct structures – water binds either as a proton donor or an acceptor. In the latter, the intramolecular H-bond is disrupted and the water molecule inserts between the OH and the aromatic ring. A second, extended anti conformer can also be detected.     

Synthese chiraler Kobalt-Komplexe mit planoid-tetradentatem Ligand-System

Synthesis of Chiral Cobalt Complexes with Planoid-Tetradentate Ligand System The synthesis of a series of Cbl-related, achiral Co^III complexes 9a – c as well as enantiomerically pure, C²-symmetric Co^III complexes 15 and 18 , is reported (Schemes 3, 5, and 7). The crystal structures of 9c and 15 were determined. Complex 18 acts as an enantioselective catalyst in the isomerization of 1,4-epiperoxides to hydroxycycloalkenones.     

An Olefinic 1,2‐Boryl‐Migration Enabled by Radical Addition: Construction of gem‐Bis(boryl)alkanes

A series of in situ formed alkenyl diboronate complexes from alkenyl Grignard reagents (commercially available or prepared from alkenyl bromides and Mg) with B₂Pin₂ (bis(pinacolato)diboron) react with diverse alkyl halides by a Ru photocatalyst to give various gem‐bis(boryl)alkanes. Alkyl radicals add efficiently to the alkenyl diboronate complexes, and the adduct radical anions undergo radical‐polar crossover, specifically, a 1,2‐boryl‐anion shift from boron to the α‐carbon sp² center. This transformation shows good functional‐group compatibility and can serve as a powerful synthetic tool for late‐stage functionalization in complex compounds. Measurements of the quantum yield reveal that a radical‐chain mechanism is operative in which the alkenyl diboronates acts as reductive quencher for the excited state of the photocatalyst.     

Columnar metallomesogens derived from unsymmetrical pyrazoles

The synthesis and mesomorphism for two series of unsymmetrical pyrazoles and their nickel(II) complexes were described. This is the first example of nickel complexes exhibiting columnar phase. The derivatives with two alkoxy chains exhibited smectic A or smectic C phases; however, all derivatives with four alkoxy chains formed hexagonal columnar phases. In contrast, all nickel(II) complexes 1a formed hexagonal columnar phases. The crystal and molecular structures of 1-(4-propyloxyphenyl)-2-(3-(4-propyloxyphenyl)-1H-pyrazol-5-yl)ethanone were determined, and it crystallizes in the triclinic space group P-1. The overall molecular shape is considered as rod-shaped. The pyrazole and one phenyl ring were coplanar, however, they were not coplanar with other phenyl ring by a dihedral angle of ca. 66.2°. A dimeric structure formed by an intermolecular H-bond (2.11 Å) and a weak π-π interaction (3.51 Å) was observed, which was probably attributed to the formation of the mesophase. The XRD experiments confirmed their structures of the mesophases.     

Ring‐opening polymerization and copolymerization of cyclic esters catalyzed by amidinate aluminum complexes

A series of new alkyl mono‐ and bimetallic aluminum complexes supported by novel amidinate ligands has been prepared in very high yields. These complexes were fully characterized by spectroscopic methods. Alkyl aluminum complexes 1 – 6 were investigated as catalysts for the ring‐opening polymerization and copolymerization of ε‐caprolactone and L‐lactide. Under the optimal reaction conditions, complex 5 acts as an efficient single‐component initiator for the ring‐opening polymerization and copolymerization of cyclic esters to yield biodegradable polyester materials with narrow polydispersities. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2397–2407