Adjacent Molecular Chains Research Articles

Synthesis and properties of novel biobased poly(hexamethylene 2,5-furandicarboxylate)-b-poly(diethylene glycol 2,5-furandicarboxylate) multiblock copolyesters

Two poly(hexamethylene 2,5-furandicarboxylate)-b-poly(diethylene glycol 2,5-furandicarboxylate) multiblock copolyesters were synthesized using two hydroxyl-terminated poly(hexamethylene 2,5-furandicarboxylate) (PHF-diol) and poly(diethylene glycol 2,5-furandicarboxylate) (PDEGF-diol) prepolymers in the presence of a chain extender hexamethylene diisocyanate. A series of techniques were employed to fully characterize the thermal, mechanical, and crystallization properties of the obtained multiblock copolyesters. 1H NMR results confirmed the expected multiblock structures. The combination of the two segments significantly improved the elongation at break of PHF without sacrificing the tensile strength. Moreover, the melt crystallization temperatures and melt points of the multiblock copolyesters only slightly decreased, due to the excellent crystallizability of the PHF segment. In addition, the PDEGF segment significantly influenced the tensile strength and hydrophilicity by forming hydrogen bonds between the adjacent molecular chains.

Facile Preparation of Lightweight Natural Rubber Nanocomposite Foams with High Wear Resistance.

The light weight and excellent mechanical properties of rubber foam means that it is widely applied in the aerospace, automobile, and military industries. However, its poor wear resistance contributes directly to a short service life and a waste of resources. Therefore, the design and development of high-wear-resistance rubber foam are of great importance. In this work, some nanoclay/rubber composite foams were prepared by blending NR/EPDM with different kinds of nanoclays containing layered double hydroxide (LDH), montmorillonite (MMT), and attapulgite (ATP) to indicate the effects of the kinds of nanoclays on the wear resistance and mechanical properties of nanoclay/rubber composite foams. The kinds of nanoclay/rubber composite foams were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The results showed that nanoclay has heterogeneous nucleation in composite foamed materials. The wear resistance of the composite foam materials with added nanoclay was significantly improved, and the MMT of the lamellar structure (increased by 43.35%) and LDH (increased by 38.57%) were significantly higher than the ATP of the rod-like structure (increased by 13.04%). The improvement in the wear resistance of the matrix was even higher. Compared with other foams, the wear resistance of the OMMT-NR/EPDM foam (increased by 58.89%) with a lamellar structure had the best wear resistance. Due to the increase in the lamellar spacing of the modified OMMT, the exfoliation of worn rubber molecular chains has little effect on the adjacent molecular chains, which prevents the occurrence of crimp wear and further improves the wear resistance of composite foaming materials. Therefore, this work lays the foundation for the manufacturing of rubber foams for wear-resistant applications.

Synthesis and crystal structure of N-(5-acetyl-4-methyl-pyrimidin-2-yl)benzene-sulfonamide.

N-(5-Acetyl-4-methyl-pyrimidin-2-yl)benzene-sulfonamide, C13H13N3O3S, was sythesized and characterized by single-crystal X-ray diffraction. In the crystal, π-π inter-actions between the phenyl and pyrimidine groups of neighbouring mol-ecules form mol-ecular chains parallel to [010]. Adjacent mol-ecular chains are linked by N-H⋯N hydrogen-bonding inter-actions between the pyrimidine and amine groups of neighbouring mol-ecules, resulting in a three-dimensional network.

The effect of cellulose molecular weight on internal structure and properties of regenerated cellulose fibers as spun from the alkali/urea aqueous system

The low-temperature alkali/urea aqueous system has received wide public attention since it is a better method to reduce pollution by preparing the regenerated cellulose fiber through the green dissolution system. Since molecular weight has a significant impact on the solubility and mechanical property of regenerated cellulose fiber; thus, we designed this experiment that cellulose materials with molecular weight ranging between 6.8 × 104 to 13.5 × 104 were employed for wet-spinning in alkali/urea aqueous system. It is found that as molecular weight of cellulose increases, cellulose solution decreases in solubility but cellulose molecular chain aggregates increase. However, bath the stability and viscosity of cellulose solutions almost remain unchanged with the change of molecular weight. As for the spun fibers, it is found that the orientation and crystallinity are relatively high when the molecular weight is low (6.8 × 104–9 × 104). These are excellent mechanical properties However, unlike conventional polymers, when molecular weight further increases to 9 × 104–13.5 × 104, the degree of orientation and crystallinity gradually decreases. This is due to a large number of entanglements between adjacent molecular chains, thereby hindering the molecular chain orientation along with reduced mechanical property. Our work demonstrates that the considerable molecular weight of cellulose is neither good for dissolution nor spun fibers' mechanical property. The choice of cellulose with relatively low molecular weight is essential not only for the excellent dissolution but also for fiber property.

A synthesized semi‐aromatic copolyamaide through synergy of three different kinds of monomers: Toward high transparency, excellent heat resistance and melt flowing property

AbstractTo fabricate the low‐cost transparent polyamide with high heat resistance and good melt flowing property simultaneously is a huge challenge in many high‐end fields due to the contradiction between these two properties. In order to balance this contradiction, in this paper, by using isophthalic acid (IPA, aromatic monomer), 4,4′‐methylenebis(cyclohexylamine) (PACM, alicyclic monomer) as rigid stereoscopic monomers, 1,6‐hexanediamine (HMD, aliphatic monomer) as the flexible monomer, a series of transparent poly(hexamethylene isophthalamide/poly(m‐benzoyl4,4′‐methylenebis(cyclohexylamine)) (PA6I/PACMI) with rigid and stereoscopic structure (corresponding to the large distance between adjacent molecular chains) were successfully synthesized. The results indicated that the newly synthesized PA6I/PACMI copolymer has an intrinsically amorphous structure and high optical transparency, which could reach as high as 90%. Furthermore, the highest glass transition temperature (Tg) of the copolymer is over 153.9°C, at the same time, the copolymer also possesses excellent melt flowing property, which can be melt processed easily. Therefore, the newly synthesized copolymer has great advantages in many fields, and it can also shed light on the design and fabrication of high‐performance materials.

Thermoelectric properties improvement in quasi-one-dimensional organic crystals

The charge and energy transport in highly conducting quasi-one-dimensional organic crystals of p-type tetrathiotetracene-iodide, TTT2I3, and of n-type tetrathiotetracene-tetracyanoquinodimethane, TTT(TCNQ)2, is studied. Two electron-phonon interactions are considered simultaneously. One interaction is of the acoustic deformation potential type and the other one is of polaronic character. Charge transport along the conducting molecular chains is bandlike, whereas in the transversal directions, it is of the hopping type. It is shown that due to a partial compensation of these interactions for a narrow interval of states in the one-dimensional conduction band, the relaxation time is of Lorentzian shape and shows a distinct dependence on carrier energy with a pronounced maximum. The scattering of charge carriers on adjacent molecular chains and by impurities and structural defects limits the height of this maximum. However, rather high relaxation times might be anticipated in the case of perfect single crystals. As the carriers in these states show an enhanced mobility, this will lead to a simultaneous increase of electrical conductivity and Seebeck coefficient. It is proposed that, if the above-mentioned crystals could be accomplished by means of sufficient purification and by optimization of the carrier concentration, so that the Fermi level is close to energetic states for which the relaxation time has a maximum, one might achieve values for the thermoelectric figure of merit ZT∼5 in crystals of tetrathiotetracene-iodide and ZT∼1.5 in those of tetrathiotetracene-tetracyanoquinodimethane.

Contact-induced stiffening in ultrathin amorphous polystyrene films

Ultrathin polystyrene (PS) films ranging from 14 nm to 316 nm were measured by atomic force microscopy (AFM) based nanomechanical mapping. Both supported and freestanding films were investigated to estimate the possible effect of the substrate. The as prepared supported ultrathin PS films show evident increase of Young's moduli and heterogeneities when the film thickness is reduced to less than 40 nm, whereas no clear thickness dependence can be found for ultrathin films after annealing. Besides, as prepared freestanding PS films thinner than 40 nm also show increased Young's moduli as decrease of the film thickness. The observed increased Young's moduli could be associated with the nano-confined film and contact load of the hard cantilever probe, where the adjacent molecular chains are perturbed and form a mechanically confined phase at the probe/polymer interface. Moreover, since as prepared and annealed ultrathin PS films show different thickness dependence in Young's moduli, it implies residual stress, confinement state of polymer chains, chain conformation, etc., which can be changed by annealing, affect the observed contact stiffening.

Thermal degradation behavior of collagen from sea cucumber (Stichopus japonicus) using TG-FTIR analysis

Collagen is the main protein of sea cucumber, and its structure and thermal properties were analyzed, which were related to the storage stability of sea cucumber. Collagen molecules (SCC) and collagen fiber from sea cucumber showed the similar amino acid composition. Fourier transform infrared (FTIR) spectra of SCC revealed amide A and I band shifted slightly when the temperature ranged from 20°C to 100°C, and X-ray diffraction indicated the distance between adjacent molecular chains decreased from 11.85Å to 11.07Å as the temperature increased from 20°C to 100°C. Thermal degradation behavior was analyzed by thermogravimetric analysis (TG) coupled with FTIR, and the degradation mechanism function of SCC could be described by G(α)=[−ln (1−α)]2/3, and the thermal degradation activation energy was in the range of 163–173kJ/mol. As the temperature increased, the amino acids in the SCC began to degrade. CO2, NH3, H2O, CH4, NO2 and HCN were released respectively along with various chemical reactions at different temperatures.

Evaluation for most probable distance between adjacent amorphous molecular chains taking preferred orientation with respect to a spinning fiber

Abstract Most probable distance between adjacent molecular chains was evaluated as the first trial for oriented amorphous polymers, using the two-dimensional radial distribution function formulated by a series expansion of Bessel and Legendre functions of coherent X-ray intensity curves. Poly(phthalazinone ether ketone) (PPEK) was selected as the test specimen, since PPEK dissolved in some solvents was one of typical amorphous polymers with high impact strength and high-temperature resistance and PPEK could produce fine fibers by dry spinning in spite of amorphous polymer. Non-crystallization of PPEK chains were analyzed in comparison with chain structure of undrawn amorphous poly(ethylene terephthalate) triggering oriented crystallization. Additionally, the strain between adjacent PPEK chains under external stress along the fiber axis was measured by a homemade instrument in relation to the chain orientation degree. These results indicated that the amorphous chains were connected with strong intermolecular force between adjacent PPEK chains, and the force could achieve fiber spinning.

A novel kind of coordination polymers employing 2,5-diamino-1,4-benzenedithiol as a bridging ligand: synthesis, structure, optical and magnetic properties

A serials of organo-soluble transition metal–DABDT coordination polymers were successfully synthesized by the coordination of transition metal ions and DABDT. These coordination polymers were characterized by FTIR, TGA, XRD, UV-Vis spectroscopy, fluorescence spectroscopy, TEM, and vibrational sample magnetometry. Results showed that DABDT coordinated transition metal ions by its amino and sulfydryl groups. The coordination polymers of Co–DABDT, Ni–DABDT, Cu–DABDT and Zn–DABDT exhibited crystal or semi-crystal characteristics, while Fe–DABDT was almost amorphous. The synthesized coordination polymers were soluble in the mixed solvent of DMF and DMSO (volume ratio, 1:1). The main UV-Vis absorptions of the as-synthesized transition metal–DABDT coordination polymers were below 400 nm in the ultraviolet region. These coordination polymers emitted cyan light in the DMF and DMSO mixed solution, especially for Zn–DABDT, which emitted obviously stronger cyan light than the other coordination polymers. Fe–DABDT exhibited superparamagnetic character in the approximate range of −5000 G to +5000 G and simple paramagnetic character in the other fields. Co–DABDT and Ni–DABDT followed simple paramagnetic behavior. TEM analysis showed that Ni–DABDT were porous nanospheres with an average diameter of about 69 nm. The rigid molecules of Ni–DABDT arrayed in parallel in the coordination polymer sphere. And Co–DABDT also showed a lamellar structure. The rigid coordination polymer molecules arrayed in parallel due to the formation of hydrogen bond between the –SH and –NH2 groups of adjacent molecular chains in the same plane. And the arrangement between different molecular layers was stacked layer upon layer on account of the π–π stacking of the coordination polymer chains. The solubility of the prepared coordination polymers enabled us to carry out a first-time study on their photophysical behavior. What's more, this is the first time to report the planar and lamellar structure of the transition metal-DABDT coordination polymers through TEM analysis.

2-(5,7-Dihydroxy-4-oxo-4H-chromen-3-yl)-5-methoxy-1,4-benzoquinone (isoflavonequinone)

In the title mol­ecule, 5,7-di­hydroxy-4′-methoxy­isoflavone­quinone, C16H10O7, the dihedral angle between the chromene moiety and the cyclo­hexa-1,4-diene ring is 51.72 (5)°. The molecular structure is stabilized by an intramolecular O—H⋯O hydrogen bond. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link the mol­ecules to form chains along the c axis. Adjacent molecular chains are linked along the b axis by C—H⋯O hydrogen bonds to form a network.

Twisted topological solitons and dislocations in a polymer crystal

Topological defects and dislocations in strongly anisotropic crystals consisting of parallel molecular chains are investigated. Our study is focused on the defects in crystalline polyethelyne, which are formed by transverse displacements of chain molecules (mutual substitutions and interlacings of adjacent molecular chains in the polymer crystal). It is shown that some of these defects called ``twisted topological solitons'' can propagate with a stationary profile and velocity. To describe the dynamics of these solitons, a model that accounts for the three components of the molecular displacements is suggested. Linear topological defects---dislocations---that incorporate the bending of molecular chains in the crystal are also studied.

Comparison of the high-pressure and low-temperature structures of ethanol and acetic acid

We have determined the high-pressure crystal structures of ethanol and acetic acid, including the positions of the hydrogen atoms, using a combination of single-crystal x-ray-diffraction techniques and ab initio pseudopotential calculations. We find that in the high-pressure structure of ethanol the molecules are arranged in infinite hydrogen-bonded chains that adopt a structural conformation that is distinctly different from that of the low-temperature form. The hydrogen-bond lengths and bond angles within the chains are equal by symmetry and, as the molecules also have an alternating alignment to the chains, the molecular chains are relatively unstrained. It is proposed that this uniformity and lack of strain within the chains enables ethanol to crystallize much more readily than methanol at high pressure. For acetic acid we find that the molecules are also arranged in infinite hydrogen-bonded chains that are essentially identical to those in the low-temperature structure. However, they adopt markedly different relative orientations, which leads to a more efficient molecular packing and a radically different methyl-methyl contact motif between adjacent molecular chains. The calculated enthalpies of the high-pressure and low-temperature structures show that the high-pressure phase is the most energetically favorable. We find a relatively small 0.056 eV/molecule enthalpy difference between the two structures and this is reflected in the very low freezing pressure of approximately 0.2 GPa at room temperature compared to the freezing temperature of $16\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ at ambient pressure.

Low-temperature piezoelectric and dielectric properties of aromatic polyureas prepared by vapour deposition polymerization

Thin films of aromatic polyurea were prepared by vapour deposition of a diisocyanate tmonomer and a diamine monomer. Three kinds of aromatic polyurea were synthesized by combining 4,4'-dipheny Lnethane diisocyanate (MDI) with 4,4'-diamino-3,3'-dimethyldiphenylmethane (MeMDA), 4,4'-diaminodiphenylether (ODA), and 4,4'-diamino-diphenylmethane (MDA). After poling, for example applying a field of 120 MV m -I at 210C for 10 min, these films acquired piezoelectric activity. The piezoelectric constant (13-26 x 10 3 C m' 2) and dielectric constant (3-4) were almost constant over a temperature range between -150C and 50 C. Infrared spectra observed for as-deposited, poled and annealed films indicated that CO and NH dipoles were oriented along the poling field and that hydrogen bonds were formed between adjacent molecular chains.

The Molecular Structure and Properties of Rubber

Abstract The molecular structure of rubber resembles that of liquids, which have a characteristic distribution of linear-chain molecules, united by transverse van der Waals forces. The x-ray diffraction diagram of undeformed rubber shows a diffuse ring, the characteristic diffraction spectrum of liquids, and this is accepted as experimental proof of the similarity between rubber and liquids. The theory that the structure of rubber involves reactive bonds in the adjacent molecular chains at short distances apart is not in accord with the relatively free rotation of these chains, which is manifest by the elastic properties of rubber, and the theory in no way distinguishes unvulcanized rubber from straight-chain paraffins. A straight-chain molecular system in which most of the links of adjacent chains are cross-bridged by van der Waals forces is a fairly rigid system, with relatively little molecular motion. The rotation of the links is equivalent to rupture of the van der Waals bonds, and in no way corresponds to the observed high degree of motion of the molecular chains in rubber, as reflected in the high elasticity of the latter. The results of the experimental study which is described in the present paper and which is concerned with the x-ray diffraction spectra of amorphous rubber and of rubber which has become crystalline by stretching, lead to the conclusion that amorphous rubber contains fragments of molecular chains, the links of which do not scatter x-rays in the form of an amorphous ring. Futhermore, the experiments offer proof of the absolutely essential role of the above-mentioned molecular structure of rubber in determining a number of properties of the rubber.

Molecular Aggregation in Amorphous Polymers

Abstract We have already established the existence of two types of packing of the links of neighboring molecular chains in amorphous rubber. The association of the links whose packing is characterized by a relatively dense distribution, similar to the packing of the molecules in low-molecular liquids, constitutes the liquid phase of amorphous rubber. In an x-ray diffraction diagram, this phase of the rubber shows an outer interference maximum caused by the intermolecular interference of the x-ray radiation which is coherently scattered by the adjacent links and corresponds to the average intermolecular spacing. Another phase of amorphous rubber, formed by the association of the segments of adjacent molecular chains, of quite disordered distribution, was called the gaseous phase. The links of the molecular chains which make up this phase of the rubber, because of their irregular distribution, scatter x-rays and show no intermolecular interference effect, so the scattering is like that in molecular gases. The dense background usually observed in diffraction diagrams of rubber, the intensity of which increases in the region of small scattering angles, can be explained by the effect of the independent scattering of the disordered links of the molecular chains of the rubber. It has the nature of scattering by a gas. The presence of such a type of molecularly disordered gaseous component is a peculiarity of the aggregation of molecules in amorphous high-molecular substances. Its existence is shown by the x-ray diffraction diagrams of amorphous high-molecular substances, in which, in the absence of low-molecular liquids, a background of independent scattering is always observed, besides the outer interference maximum which corresponds to the intermolecular spacing. The intensity I of the scattered (monochromatic) x-rays at any angle is, according to the theories developed, determined by the sum of the scattering intensities of the gaseous (Ig) and liquid (Il) phases of the amorphous substance.