Structure of the hard segments in trans,trans-diisocyanato dicyclohexylmethane based PU elastomers

A model for the structure of the hard segments and the hydrogen bonded network in the hard domains of segmented polyurethane elastomers with trans,trans-diisocyanato dicyclohexylmethane (tt-HMDI)/1,4-butanediol (BDO) based hard segments is proposed. The structure of the bis(methylurethane) oftt-HMDI (Me-ttHMDI-Me) has been determined by single crystal x-ray diffraction analysis and the conformation and packing of the polyurethane hard segments are constructed by connecting the successive Me-ttHMDI-Me units via –CH₂–CH₂– groups using the principle of isomorphic substitution. The conformation and hydrogen bonds of the monomer units are retained. The resulting polyurethane structure is highly crosslinked by a three-dimensional hydrogen bond network. The special packing principle may explain the high melting point as compared to the well-known structure of 4,4-diisocyanato diphenylmethane (MDI)-BDO hard segments and the differences in the material properties.     

Preparation and properties of polyesters from diphenylmethane-4,4′-di(methylthiopropionic acid) and aliphatic diols

The new linear polyesters containing sulfur in the main chain were obtained by melt polycondensation of diphenylmethane-4,4′-di(methylthiopropionic acid) with ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propanediol, 1,3-butanediol, and 2,2′-oxydiethanol. Low-molecular weights, low-softening temperatures and, very good solubility in organic solvents are their characteristics. The structure of all polyesters was determined by elemental analysis, FT-IR and ¹H-NMR spectroscopy, and x-ray diffraction analysis. The thermal behavior of these polymers was examined by differential thermal analysis (DTA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The kinetics of polyesters formation by uncatalyzed melt polycondensation was studied in a model system: diphenylmethane-4,4′-di(methylthiopropionic acid) and 1,4-butanediol or 2,2′-oxydiethanol at 150, 160, and 170°C. Reaction rate constants (k₃) and activation parameters (ΔG^≠, ΔH^≠, ΔS^≠) from carboxyl group loss were determined using classical kinetic methods. © 1997 John Wiley & Sons, Inc.     

Compositional effect on the morphology and ionic conductivity of thermoplastic polyurethane based electrolytes

Four thermoplastic polyurethanes (TPUs) were synthesized from poly(ethylene glycol) (PEG), 4,4^′-methylenebis(phenyl isocyanate) (MDI), and 1,4-butanediol (1,4-BDO) with different 1,4-BDO/PEG ratios. The effect of polymer structure on the conductivity of the polymer elelctrolytes was investigated. Fourier transform infrared spectroscopy (FT-ir) and differential scanning calorimetry (DSC) were utilized to monitor changes in the morphology of the TPUs as polymeric solid electrolyte doped with LiClO₄. The structure of the TPUs has been investigated by 1H solution nuclear magnetic resonance spectroscopy. Alternating current (AC) impedance experiments were performed to determine the ionic conductivities of TPU films and their corresponding gel type electrolytes. The conductivity depends on the soft-segment concentration and on the degree of phase separation exhibited by these materials. One of the investigated TPU gel type electrolytes exhibits an ionic conductivity as high as 3×10⁻⁴ S/cm at room temperature.     

Polyterephthalates of 2,3-disubstituted butanediols-1,4: Effect of aliphatic substituents on Tg and Tm of the polyesters

Poly(2,3-dialkylbutanediol-1,4 terephthalates) with the alkyl substituents CH₃, C₂H₅, n-C₃H₇, iso-C₃H₇, n-C₄H₉, and n-C₁₀H₂₁, andn-C₁₆H₃₃ were synthesized from the corresponding 2,3-dialkylbutanediols-1,4 and dimethyl terephthalate or terephthaloyl chloride. The substituents of the butanediol-1,4 portion of the polyterephthalates influence the ¹³C NMR chemical shifts of the carbon atoms near the branching site, the glass transition (T_g), and the crystallizability. Small alkyl substituents do not change the T_g of the polymers, whereas bulky substituents such as the isopropyl group increase the T_g and long normal alkyl groups as substituents decrease the T_g of the polymers. Crystallinity in these polyterephthalates was found only with CH₃ and C₁₆H₃₃ as the 2,3-dialkyl substituents in the butanediol-1,4 portion of the polyester. This crystallinity of polyterephthalate of 2,3-di-C₁₆H₃₃ substituted butanediol-1,4 could be assigned to side-chain crystallization of the paraffinic groups.     

Random thermotropic elastomers. I. Effects of substitution and hard/soft segment lengths on properties

Syntheses of segmented copoly(ether-ester)s with (oxy-2-methyl-1,4-phenyleneoxycarbonyl-1,4-phenylene carbonyl)/(oxy-2-chloro-1,4-phenyleneoxycarbonyl-1,4-phenylene carbonyl) (methyl-/chloro-substituted) hard segments and poly(oxytetramethylene) soft segments, are reported. The methodology consisted of staged addition melt condensation of terephthaloyl chloride, poly(oxytetramethylene)glycol (POTMG; \[ \bar M_n \] = 250, 650, 1000, 2000) and methyl-/chloro-hydroquinone. Lengths of hard and soft segments were varied while the weight ratio of hard to soft segment was maintained constant. Copolymers were characterised for solubility behavior, and by infrared spectroscopy, x-ray diffraction, DSC, and polarizing microscopy. Thermal properties were found to be dependent on length of soft segment as well as on the type of substituent in the mesogenic core. In both methyl- as well as chloro-substituted copoly(ether-ester)s soft segment glass transition temperature (T_gs) was obtained between ?40 and ?50°C. All copoly(ether-ester)s are elastomeric at room temperature (25°C). These polymers exhibit thermotropic liquid crystalline behavior and were easily sheared and aligned in liquid crystalline state. © 1994 John Wiley & Sons, Inc.     

Synthesis and Reactivity of a Bio‐inspired Dithiolene Ligand and its Mo Oxo Complex

An original synthesis of the fused pyranoquinoxaline dithiolene ligand qpdt^2? is discussed in detail. The most intriguing step is the introduction of the dithiolene moiety by Pd‐catalyzed carbon–sulfur coupling. The corresponding Mo^IVO complex (Bu₄N)₂[MoO(qpdt)₂] ( 2 ) underwent reversible protonation in a strongly acidic medium and remained stable under anaerobic conditions. Besides, 2 was found to be very sensitive towards oxygen, as upon oxidation it formed a planar dithiin derivative. Moreover, the qpdt^2? ligand in the presence of [MoCl₄(tBuNC)₂] formed a tetracyclic structure. The products resulting from the unique reactivity of qpdt^2? were characterized by X‐ray diffraction, mass spectrometry, NMR spectroscopy, UV/Vis spectroscopy, and electrochemistry. Plausible mechanisms for the formation of these products are also proposed.     

Synthesis and thermal transition behavior of model thermoplastic polyurethanes containing MDI/butanediol‐based monodisperse hard segments

Amine‐terminated monodisperse hard segments (MDHSs) containing two to four 4,4′‐methylenebis (phenyl isocyanate) extended by 1,4‐butanediol have been synthesized using carboxybenzyl protecting‐deprotecting strategy. Pure MDHSs in large scale were obtained in good yield and their structures were confirmed by ¹H‐, ¹³C‐NMR spectroscopy and GPC‐MALLS. Differential scanning calorimetry (DSC) showed that as the hard segment (HS) size increased, the melting and glass transition temperature and the change of heat capacity at glass transition of ethyl capped MDHSs increased. Model thermoplastic polyurethanes (TPUs) were synthesized using the reaction of bischloroformate of poly (tetramethylene oxide) (PTMO) diol or polyisobutylene (PIB) diol with amine‐terminated MDHSs. X‐ray diffraction results indicated the amorphous structure of model TPUs. DSC revealed HS related endotherms, regardless of SS, which were attributed to the local ordering of the HSs. Additional endotherms in PTMO based model TPUs might arise from the dissociation of hydrogen bonding between PTMO and HSs. The lower T_g in model TPUs compared to the polydisperse analogues observed by dynamic mechanical analysis (DMA) indicated higher microphase separation of monodisperse HSs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3171–3181     

环氧乙烷-四氢呋喃共聚醚基热塑性聚氨酯弹性体氢键体系的定量研究

氢键为热塑性聚氨酯弹性体内的重要键合力特征。该文基于氢键所引起基团的频移,以FTIR为主要的研究手段,并结合通过动态力学性能（DMA）研究所建立的评估硬段与软段之间混溶的定量方程,对所合成的以环氧乙烷－四氢呋喃无规共聚醚、2,4－甲苯二异氰酸酯以及1,4－丁二醇为原料的热塑性聚醚聚氨酯弹性体的氢键体系进行了定量化研究。结果表明,大约有30％的硬段混溶进入炊段相对软段的醚氧产生氢键作用,主要的氢键包括硬段羰基与硬段氨基之间的氢键以及硬段烷氧与硬段氨基之间的氢键,仍发生在硬段岛区内。     

Coordination polymers. VIII. IR spectroscopic studies on the mechanism of the reaction between polyesters and zinc oxide

This article was written for the purpose of investigating the mechanisms of reactions between unsaturated polyester resins and base anhydridelike metal oxides (CaO, MgO, ZnO) which cause an increase in viscosity. As a model system ethyl-hydrogen-succinate (ESH) and ZnO were reacted in CCl₄ and complexes that contained Zn-hydroxocarboxylate units took an essential part in this reaction. Solubility measurements of the model compounds and infrared (IR) spectra of the reaction products led to the conclusion that further molecular associates were formed from the mixed metal-hydroxocarboxylate complex by the carbonyl oxygens of ester groups, which resulted in end products of polymeric structure. It is suggested by IR spectroscopical analogies between the model compounds and reaction products of an adipic acid/butanediol-1,4 polyester with ZnO that similar reactions can account for the polyesters as well.     

Influence of TiO2 particles and APP on combustion behavior and mechanical properties of flame-retardant thermoplastic polyurethane

The experimental investigation on combustion behavior and mechanical properties of flame-retardant thermoplastic polyurethane were performed in the article. By the masterbatch-melt blending technique, the TiO₂ particles were well dispersed in TPU/APP composites. The microscopic morphology structure was observed by TEM and SEM. TEM images of TPU–TiO₂ masterbatch material showed that the grain sizes of TiO₂ particles were 200–400 nm. The SEM result indicated that the TiO₂ particles could enhance compatibility and dispersion of APP in TPU. The mechanical properties of TPU composites were characterized by dynamic mechanical analysis (DMA) and tensile tests, respectively. The DMA results indicated that TiO₂ particles could improve the viscoelastic property of the TPU/APP composites. The tensile strength achieved a significant improvement with addition of TiO₂ particles. APP/TiO₂-5 obtains a better value of 344% than APP-1 (277%). Also, the flame-retardant property and thermal stability of the TPU composites were characterized using cone calorimeter test (CCT) and thermogravimetric analysis (TGA), respectively. The CCT results revealed that TiO₂ particles could enhance the flame-retardant property of APP in TPU. The peak heat release rate of APP/TiO₂-4 containing 0.5% TiO₂ decreased to 157.27 kW m^?2 from 225.5 kW m^?2 of APP-1 sample without any TiO₂. The TiO₂ particles could promote the formation of carbon layers which restrict the diffusion of fuels into combustion zone and access of oxygen to the underlying materials. The TGA results indicated that TiO₂ can improve the thermal stability of TPU/APP composites.

     

Neutron Diffraction and TEM Studies of the Crystal Structure and Defects of Nd4Ni3O8

Powder neutron diffraction and electron microscopy studies confirmed the crystal structure of Nd₄Ni₃O₈(space groupI4/mmm;a=b=3.9168(2) Å,c=25.322(2) Å,Z=4; reliability factorsR_p=0.125,R_wp=0.108,χ²=2.81,R_Bragg=0.043,R_F=0.037) previously determined by powder X-ray diffraction [Ph. Lacorre,J. Solid State Chem.97, 495 (1992)]. It consists in the intergrowth between triple layers of nickel in square planar coordination with Nd in cubic coordination (infinite layer type) and fluorite type layers. Nd₄Ni₃O₈is thus the first known compound with a triple T′ type structure (relative to the single T′ type structure of Nd₂CuO₄). A study of the coherent diffraction lengths and defects in the structure has been carried out. Two kinds of defects have been detected by HREM, for which a model is proposed.     

Syntheses,Structures, and Catalytic Properties of Three Copper(II) Coordination Polymers Based on 2,3,5,6‐Tetrafluoro‐1,4‐bis(triazole‐ylmethyl)benzene and Benzene Carboxylate Ligands

Three new mixed‐ligand coordination polymers of Cu^II, namely, [Cu(Fbtx)(L1)(H₂O)]_n ( 1 ), [Cu(Fbtx)_0.5(HL2)(H₂O)₂]_n ( 2 ), and {[Cu(Fbtx)_1.5(HL3)(H₂O)] · H₂O}_n ( 3 ) [Fbtx = 2,3,5,6‐tetrafluoro‐1,4‐bis(1,2,4‐triazole‐1‐ylmethyl)benenze, H₂L1 = terephthalic acid, H₃L2 = trimesic acid, NaH₂L3 = 5‐sulfoisophthalic acid monosodium salt], were hydrothermally synthesized and structurally characterized by elemental analysis, IR spectra, and single‐crystal and powder X‐ray diffraction techniques. All the complexes have a two‐dimensional (2D) coordination layer structure. Of these, 1 displays a planar 4⁴‐ sql structure whereas both 2 and 3 are highly undulated 6³‐ hcb nets. Moreover, their thermal stability and catalytic behaviors in the aerobic oxidation of 4‐methoxybenzyl alcohol were also investigated as well. The results indicate that the benzene dicarboxylate ligands have an effective influence on the structures and catalytic properties of the resulting coordination polymers.     

Motional heterogeneity and phase separation of functionalized polyester polyurethanes

The polyester polyurethanes, PU based on isophoronediisocyanate, polycaprolactone, and 1,4-butanediol with different amounts of functional groups introduced into the hard segments via second chain extender, 2,2′-bis-(hydroxymethyl) propionic acid, were investigated by electron spin resonance, ESR, spin label method, wide-angle X-ray diffraction, WAXD, optical microscopy and differential scanning calorimetry, DSC. The objective of this study is to clarify the effect of functional groups on the motional heterogeneity, microphase separation and crystallisation of the polyurethanes. The concentration of carboxylic groups varied from 0 to 0.45 mmol g⁻¹. The temperature-dependent ESR spectra of spin labelled PU hard segments chain ends with stable nitroxide radical 2,2,6,6-tetramethyl-4-aminopiperidin-1-yloxyl are sensitive to the amount of functional groups attached to the hard segments. Composite ESR spectra of functionalized PU, with fast and slow component, suggest that PU hard segments are partitioned in two motionally different environments. According to the ratio of fast and slow component motional heterogeneity increases with an increase of functional groups up to 0.35 mmol g⁻¹ and above this concentration slow component decreases indicating higher degree of phase mixing and stronger effect of soft segments. Polarized micrographs and the extent of ordering from WAXD measurements reveal the changes of phase morphology with the carboxylic groups content in a similar way as shown from the motional behaviour of spin label on the segmental level. The degree of crystallinity and the separation of spherulitic rings are decreasing above a certain concentration of functional groups. The effect of functional groups in PU on the hard and soft segment mixing is discussed in terms of additional noncovalent interactions and chain structure which at critical level of interactions lead to a formation of more open hard segment structure accessible to interaction with the soft segment.     

A New Coordination Polymer [Pb(1,4‐BDC)]n Containing a Unique μ6‐Bridging Coordination Mode

A new coordination polymer, [Pb(1,4‐BDC)]_n ( 1 ) (1,4‐H₂BDC = 1,4‐benzenedicarboxylic acid), has been synthesized under solvothermal conditions. Its structure was determined with single‐crystal X‐ray diffraction studies and further characterized by inductively coupled plasma (ICP) spectrometry, elemental analysis, IR spectroscopy, thermogravimetric analysis, and X‐ray powder diffraction studies. The results revealed that complex 1 has a two‐dimensional network with (6, 3) topology observed in the [110] direction. Moreover, the layers are connected into a framework through 1,4‐BDC^2? ligands. The μ₆‐bridging coordination mode adopted by 1,4‐BDC^2? is unprecedented in metal/1,4‐BDC^2? complexes.     

Structure,spectroscopy and magnetism of 1,4-dihydro-1,4-diazine radical cations: Exceptionally stable intermediates related to methylviologen and flavosemiquinone radicals

-1,4-Dialkyl-1,4-dihydro-1,4-diazine radical cations 1–3 have been established in recent years as unusually stable intermediates of corresponding two-step redox systems. The stability is evident from large comproportionation constants K_c > 10¹² and from the isolability of persistent radical cation salts with counter anions such as Br^-, I^-, I₃ ^-, PF₆ ^-, BPh4-, or (TCNQ₂)^-. The structures of several crystalline derivatives have been determined, showing planar π systems and, in one instance, an anion-dependent tendency to form π/π dimers. Effects of dimerization are also evident from comparative magnetic susceptibility measurements of 1,4-diethyl-1,4-dihydroquinoxalinium iodide and tetraphenylborate. UV/Vis absorption spectra of the radical cations have been determined and interpreted with the help of molecular orbital calculations. The most simple member of the series, 1,4-diethyl-1,4-dihydropyrazinum radical cation 1, exhibits a long wavelength forbidden band (²B_1u → ²A_u) with a conspicuous vibrational fine structure. The results obtained for the small but very stable new radical cations 1 and 2 provide clues to the stability of flavosemiquinone oxidation states in pertinent oxidoreductase enzymes and show ways to new components for the design of materials with anisotropic physical properties.     

Synthesis,crystal structure and photophysical properties of 1,4‐bis(1,3‐diazaazulen‐2‐yl)benzene: a new π building block

A dimerized 1,3‐diazaazulene derivative, namely 1,4‐bis(1,3‐diazaazulen‐2‐yl)benzene [or 2,2′‐(1,4‐phenylene)bis(1,3‐diazaazulene)], C₂₂H₁₄N₄, (I), has been synthesized successfully through the condensation reaction between 2‐methoxytropone and benzene‐1,4‐dicarboximidamide hydrochloride, and was characterized by ¹H NMR and ¹³C NMR spectroscopies, and ESI–MS. X‐ray diffraction analysis reveals that (I) has a nearly planar structure with good π‐electron delocalization, indicating that it might serve as a π building block. The crystal belongs to the monoclinic system. One‐dimensional chains were formed along the a axis through π–π interactions and adjacent chains are stabilized by C—H…N interactions, forming a three‐dimensional architecture. The solid emission of (I) in the crystalline form exhibited a 170 nm red shift compared with that in the solution state. The observed optical bandgap for (I) is 3.22 eV and a cyclic voltammetry experiment confirmed the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The calculated bandgap for (I) is 3.37 eV, which is very close to the experimental result. In addition, the polarizability and hyperpolarizability of (I) were appraised for its further application in second‐order nonlinear optical materials.     

Synthesis of Tetraoxygenated Terephthalates via a Dichloroquinone Route: Characterization of Cross‐Conjugated Liebermann Betaine Intermediates

Cross‐conjugated quinoid betaines 4 (2,5‐bis(alkoxycarbonyl)‐3,6‐dioxo‐4‐(1‐pyridinium‐1‐yl)cyclohexa‐1,4‐dien‐1‐olates; Liebermann betaines) were synthesized from 2,5‐dichloro‐3,6‐dioxocyclohexa‐1,4‐diene‐1,4‐dicarboxylates ( 2 ) and pyridines in acetone containing H₂O. Their structure was secured by NMR spectroscopy and by X‐ray diffraction analysis of 4f (alkoxy = EtO, pyridine = 4‐Me₂N–C₅H₄N). Betaines 4 show comparatively high reactivity towards nucleophiles as a consequence of their cross‐conjugated character. Betaine 4a and hydroxy‐3,4‐methylenedioxybenzene (sesamol) condense to give a pyridinium quinolate salt 14 which has a bifurcate H‐bond from a pyridinium N⁺–H donor to both carbonyl (C=O) and olate (C–O⁻) acceptors in the solid state. Betaine 4b hydrolyzes in aqueous solution to give diethyl 2,5‐dihydroxy‐3,6‐dioxocyclohexa‐1,4‐diene‐1,4‐dicarboxylate ( 11 ) as a pyridinium salt, or as polymeric zinc(II) complex of the dianion of 11 in the presence of ZnCl₂. Dihydroxyquinone 11 was analytically differentiated from its independently prepared hydroquinone form, diethyl 2,3,5,6‐tetrahydroxyterephthalate ( 12 ), by NMR analysis in solution and X‐ray crystal structure determination of both compounds.     

Molecular Structure of the Bis[tris(2-aminoethyl)aminecyano]dicobalt(III) Ion and its UV/VIS Spectrum

Formation of μ-peroxodicobalt(III) complexes has been studied in solutions containing tris(2-aminoethyl)aminecobalt(II) and additional monodentate ligands X. Depending n the nature and the concentration of X and on pH, singly bridged [(tren)XCoOOCoX(tren)]⁴⁺ and/or doubly bridged [(tren)Co(C₂OH)Co(tren)]³⁺ are formed. The UV/VIS spectra of these complexes are discussed on the basis of a theoretical model which stresses the importance of the dihedral angle of the CoOOCo-group. [(tren)(CN)CoOOCo(CN)(tren)](ClO₄)₂ has been synthesized and its structure determined by single crystal X-ray diffraction. The CoOOCo-group of the cation is planar. Solutions of the complex as well as the solid show two CT bands in the 300–400 nm region.     

The preferred conformation of cis-1,4-dihydro-4-tritylbiphenyl: A flexible cyclohexa-1,4-diene

X-ray crystallographic and solution ¹H n.m.r. studies of $\text{cis}$-1,4-dihydro-4-tritylbiphenyl (2) both suggest the presence of an almost planar cyclohexa-1,4-diene ring (α_mean = 1975°).⁴     

Copper(I) π‐Complexes with 2‐Butyne‐1,4‐diol. Synthesis and Crystal Structure of Na[CuCl2(HOCH2C≡CCH2OH)]·2H2O

Crystals of anionic Na[CuCl₂(HOCH₂C≡CCH₂OH)]·2H₂O π‐complex have been synthesized by interaction of 2‐butyne‐1,4‐diol with CuCl in a concentrated aqueous NaCl solution and characterized by X‐ray diffraction at 100 K. The crystals are triclinic: space group , a = 7.142(3), b = 7.703(3), c = 10.425(4) Å, α = 105.60(3), β = 99.49(3), γ = 110.43(3)°, V = 495.9(4) ų, Z = 2, R = 0.0203 for 3496 reflections. The structure is built of discrete [CuCl₂(HOCH₂C≡CCH₂OH)]^? anionic stacks and polymeric cations among the stacks. The Cu^I atom adopts trigonal planar coordination of two Cl^? anions and the C≡C bond of 2‐butyne‐1,4‐diol, Cu–(C≡C) distance is equal to 1.903(3) Å. Na⁺ cations environment is octahedral and consists of O and Cl atoms. The crystal packing is governed by strong hydrogen bonds of O–H···Cl and O–H···O types.