Dynamic mechanical properties of extruded rods of poly(dimethylsilylene‐co‐methyl‐n‐propylsilylene)

Tractable polysilanes were prepared by the copolymerization of a methyl‐n‐propylsilylene (MP) unit into poly(dimethylsilylene), which neither dissolves in common solvents nor melts before decomposition. Although poly(dimethylsilylene‐co‐methyl‐n‐propylsilylene) has poor solubility in the composition range of the dimethylsilylene (DM) unit to the MP unit (DM/MP = 7/3 ∼ 9/1), the copolymers form the columnar mesophase at elevated temperatures. Highly oriented rods were prepared via the extrusion of the copolymers with a circular tube die in a temperature range in which the transition to the columnar mesophase began to occur (70°C when DM/MP = 7/3 and 8/2 and 120°C when DM/MP = 9/1). The extruded rods were characterized in detail by dynamic viscoelasticity and wide‐angle X‐ray diffraction (WAXD) to clarify the structure–mechanical‐property relationship. The orientation functions of the extruded rods were determined by the azimuthal intensity distribution of the WAXD reflection. The orientation function and dynamic storage modulus increased with an increasing extrusion ratio. The dynamic storage modulus at −150°C was 8 ∼ 10 GPa at the highest extrusion ratio and correlated well with the crystal orientation function. The dynamic storage modulus at room temperature was lowered by the structural relaxations at −100 ∼ +30°C, which corresponded to the molecular motion of the rigid molecular chains of the copolymer and the local molecular motion of the MP unit. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 698–706, 2000     

Suppression of Thermochromism in a Poly(di‐n‐hexylsilane)‐Zirconia Hybrid

Summary: Poly(di‐n‐hexylsilane) (PDHS)‐containing zirconia hybrid thin films were prepared by a sol‐gel reaction of PDHS copolymers and zirconium alkoxide, and it was found that the thermochromic properties of PDHS due to the transformation of the Si Si main chain were suppressed in the PDHS‐zirconia hybrid thin film.

Structure of poly(di‐n‐hexylsilane)‐zirconia hybrid.     

Packing Studies on Poly(di‐n‐alkylsilylenemethylene)s

The packing of poly(di‐n‐alkylsilylenemethylene) (PDASMs) chains was studied by using X‐ray, electron diffraction, and molecular modeling methods. X‐ray and electron diffraction measurements revealed unit cells in which the PDASMs were efficiently packed. The PDASM with the longer alkyl side chains, such as poly(di‐n‐propylsilylenemethylene) (PDPrSM), showed packing with the alkyl side chains interlocked with each other like cross‐shaped gears in the two‐dimensional monoclinic unit cell. The PDASM with the shorter ethyl substituent, poly(di‐n‐ethylsilylenemethylene) (PDESM), showed a lack of ability to interlock its side chains due to the short length of the alkyl groups. In these studies, we found that the length of the alkyl side chains could change the packing arrangement of PDASMs from monoclinic to orthorhombic to hexagonal with only short‐range order as the alkyl side chain length decreases at room temperature.

The ab projection of a 4 × 4 chain array of poly(di‐n‐propylsilylenemethylene) (PDPSM) in the monoclinic unit cell.     

Crystallographic report: Phenyl(N,N‐di‐n‐propyldithiocarbamato)mercury(II)

The structure of PhHg(S₂CNPr₂) shows a distorted linear geometry about mercury defined by a sulfur and a carbon atom. Centrosymmetric molecules aggregate via Hg?S interactions to form loosely associated dimers. Copyright © 2003 John Wiley & Sons, Ltd.     

Engineering a sharp physiological transition state for poly(n‐isopropylacrylamide) through structural control

Poly(N‐isopropylacrylamide) (pNIPAAm), a well‐studied, biologically inert polymer that undergoes a sharp aqueous thermal transition at 32 °C, has been a subject of widespread interest for possible biological applications. A major hindrance to its successful application is due to the difficulty of maintaining a sharp transition when the polymer is modified for a physiological transition temperature, especially in isotonic solutions. Current copolymer blends raise the transition temperature but also make the transition significantly broader. We have combined the use of reversible addition‐fragmentation chain transfer (RAFT) polymerization with tacticity control to synthesize well‐defined pNIPAAm that demonstrates sharp transitions under physiological conditions. By selecting a RAFT agent with appropriate end groups, controlling molecular weight, and increasing the racemo diad content, we were able to increase the thermal transition temperature of pure pNIPAAm to a sharp transition at 37.6 °C under isotonic conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of polyethylene oxide graft polysilylenes and networks based on poly(di‐n‐pentylsilylene/n‐pentyloct‐7‐enyl) copolymers

Poly(dipentylsilylene) copolymers containing n‐pentyl‐n‐oct‐7‐enylsilane units were prepared by reductive coupling of the corresponding dichlorosilanes. Linear high molecular weight and some crosslinked polymer were obtained. The soluble products exhibited optical and thermal properties like poly(dipentylsilylene). Differential scanning calorimetry was used to investigate crystallization and to monitor thermal crosslinking. Vinyl functionalized side chains were hydrosilylated with dipentylsilane and dimethylchlorosilane and crosslinked via the side chains. Hydrosilylation with di‐n‐pentyl(trimethylsiloxypropyl)silane led to a partial hydroxy functionalization of the polysilylene and enabled anionic PEO grafting of the poly(dipentylsilylene). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2306–2318, 2000     

Crystalline structure of poly(methyl-n-propylsilane)

The thermal behavior and physical structure of atactic poly(methyl-n-propylsilane) (PMPrS) have been investigated by complementary techniques. Temperature-dependent wide-angle X-ray scattering as well as thermal analysis clearly indicate that atactic PMPrS crystallizes below 40°C in a monoclinic lattice with PMPrS adopting an all-trans planar zigzag conformation. Above 40°C, the polymer is in the isotropic amorphous state. A restricted analysis of the structure factors of PMPrS has been performed, indicating that the zigzag planes most probably lie in (1 10) planes. The chains pack with little interpenetration, and the crystals may be considered as bundles of long, closely packed prisms. The restricted interlocking of neighboring chains results, in turn, in a poor register of the chains along the c-axis. Moreover, transmission electron microscopy reveals that the crystallized polymer adopts a lamellar microstructure, with parallel lamellae tending to form tight bundles. Both electron microscopy and small-angle X-ray scattering indicate crystal thicknesses of about 60 Å. Finally, PMPrS was found to crystallize with a nucleation-controlled type of kinetics. Avrami exponents were calculated as n ≈ 1, suggesting a fibrillar growth geometry compatible with the absence of spherulitic superstructure. A double-melting behavior is also observed for PMPrS. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1533–1543, 1997     

Two polymorphs of N‐(2‐methoxyphenyl)‐4‐oxo‐4H‐chromone‐3‐carboxamide

The title compound, C₁₇H₁₃NO₄, crystallizes in two polymorphic forms, each with two molecules in the asymmetric unit and in the monoclinic space group P2₁/c. All of the molecules have intramolecular hydrogen bonds involving the amide group. The amide N atoms act as donors to the carbonyl group of the pyrone and also to the methoxy group of the benzene ring. The carbonyl O atom of the amide group acts as an acceptor of the β and β′ C atoms belonging to the aromatic rings. These intramolecular hydrogen bonds have a profound effect on the molecular conformation. In one polymorph, the molecules in the asymmetric unit are linked to form dimers by weak C—H...O interactions. In the other, the molecules in the asymmetric unit are linked by a single weak C—H...O hydrogen bond. Two of these units are linked to form centrosymmetric tetramers by a second weak C—H...O interaction. Further interactions of this type link the molecules into chains, so forming a three‐dimensional network. These interactions in both polymorphs are supplemented by π–π interactions between the chromone rings and between the chromone and methoxyphenyl rings.     

Synthesis of poly(γ-methoxypropylmethylsilylene) and poly(γ-methoxypropylmethylsilylene-co-di-n-hexylsilylene)

The synthesis of γ;-methoxypropylmethyldichlorosilane, and its subsequent polymerization and copolymerization with di;-n;-hexyldichlorosilane through the reductive coupling with sodium has been accomplished. The resulting polymers contain methyl ether side groups that allow further synthetic transformations on the polysilane backbone. For poly (γ;-methoxypropylmethylsilylene) these groups impart solubility characteristics different than typical alkyl and aryl substituted polysilanes. These new polymers and copolymers have been characterized by GPC and ¹H-, ¹³C-, and ²⁹Si-NMR. © 1994 John Wiley & Sons, Inc.     

Viscoelastic and damping characteristics of poly(n‐butyl acrylate)‐poly(n‐butyl methacrylate) semi‐IPN latex films

This article reports the synthesis, characterization, and damping characteristics of semi‐interpenetrating (semi‐IPN) latex systems composed of poly n‐butyl acrylate (PBA) core and poly n‐butyl methacrylate (PBMA) shell. The IPN's were prepared by seeded emulsion polymerization using crosslinked PBA seeds with varying crosslinker (m‐diisopropenyl benzene) concentration. The polymer weight ratio in the first and second stage polymerization is maintained at 1:1 in all the cases. The particle size determined by dynamic light scattering shows a decrease in the shell thickness with increasing crosslinker concentration of the seed. The mechanical properties, like Shore A hardness of the films, increased from 18 to 65 when the crosslinker concentration is increased from 0 to 4.8 mol%. The dynamic mechanical studies show that the modulus value of the IPN's is below that of non‐crosslinked films, and the value depends upon the crosslink density of the seed. Mechanical models, such as the Kerner's model and the Takayanagi's model, were used to explain the variation in the dynamic mechanical properties with the degree of seed crosslinking. The study indicates lower bound (rubbery) behavior for the films with lightly crosslinked cores. The study also shows that, at lower crosslinker concentration enhanced phase separation and better damping properties are achieved but at higher cross linker concentration (>2 mol%) greater interpenetration of the shell monomer to the cores takes place and tough films, with reduced damping properties are formed. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of n‐type doping on the hole transport in poly(p‐phenylene vinylene)

N‐type doping of poly(2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene vinylene) (MEH‐PPV) with decamethylcobaltocene (DMC) strongly improves the electron transport due to filling of the electron traps. Unexpectedly, the n‐type doping simultaneously suppresses the hole transport in MEH‐PPV. We demonstrate that this strong reduction of the hole transport originates from unionized DMC molecules that act as hole traps. This hole trapping effect explains why the current of a DMC‐doped MEH‐PPV polymer light‐emitting diode is orders of magnitude lower than that of the undoped device. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Degradation of poly(methylphenylsilylene) and poly(di-n-hexylsilylene)

Degradation of poly(methylphenylsiylene) and poly(di-n-hexylsilylene) was studied by chemical and mechanical methods at ambient and higher temperatures. Purely thermal degradation in solid state starts as a slow process at 150°C and provides soluble and insoluble products which include cyclosilanes as well as various siloxanes. Sonication at ambient temperatures leads to the mechanical degradation of high molecular weight polymers by homolytic cleavage induced by shear forces. No cyclics are formed under these conditions. Polysilanes in the presence of strong nucleophiles degrade exclusively to cyclic oligomers. Rate of this back-biting chain reaction depends on substituents at silicon atom, alkali metal, solvents, and temperature. Electrophiles degrade polysilanes to various α,ω-difunctional oligosilanes. © 1993 John Wiley & Sons, Inc.     

Molecular composites made of ionic poly(p‐phenylene terephthalamide) and poly(4‐vinylpyridine): Deformation modes

Deformation modes were examined on strained thin films of a series of molecular composites containing ionically modified rodlike molecules of poly(p‐phenylene terephthalamide) (PPTA) dispersed in a polar polymer matrix. The rigid molecules were a modified form of PPTA in which the H atom of the amide group was replaced, on 30 mol % of the monomer units, by an ionic propane sulfonate group. The polar polymer matrix of these composites was the flexible‐coil polymer, poly(4‐vinylpyridine). Ionic interactions between the two components increased the effective entanglement strand density and produced changes in the deformation modes. The observed changes were dependent on the relative concentration of the two components and on the nature of the counterion. With K⁺ as the counterion, the induced deformation mode changed from pure crazing, as in the matrix polymer, to combined crazing and shear deformation at 5 wt % of the ionic polymer and to essentially pure shear deformation as the concentration increased to 15 wt %. However, when Ca²⁺ was the counterion, pure shear deformation developed at a concentration of only 5 wt %. This effect was attributed to a greater ionic interaction and to a higher effective strand density of the composites, when monovalent K⁺ was replaced by divalent Ca²⁺. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 429–436, 2003     

Different molecular conformations co‐exist in each of three 2‐aryl‐N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)acetamides: hydrogen bonding in zero,one and two dimensions

4‐Antipyrine [4‐amino‐1,5‐dimethyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐one] and its derivatives exhibit a range of biological activities, including analgesic, antibacterial and anti‐inflammatory, and new examples are always of potential interest and value. 2‐(4‐Chlorophenyl)‐N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)acetamide, C₁₉H₁₈ClN₃O₂, (I), crystallizes with Z′ = 2 in the space group P, whereas its positional isomer 2‐(2‐chlorophenyl)‐N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)acetamide, (II), crystallizes with Z′ = 1 in the space group C2/c; the molecules of (II) are disordered over two sets of atomic sites having occupancies of 0.6020 (18) and 0.3980 (18). The two independent molecules of (I) adopt different molecular conformations, as do the two disorder components in (II), where the 2‐chlorophenyl substituents adopt different orientations. The molecules of (I) are linked by a combination of N—H…O and C—H…O hydrogen bonds to form centrosymmetric four‐molecule aggregates, while those of (II) are linked by the same types of hydrogen bonds forming sheets. The related compound N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)‐2‐(3‐methoxyphenyl)acetamide, C₂₀H₂₁N₃O₃, (III), is isomorphous with (I) but not strictly isostructural; again the two independent molecules adopt different molecular conformations, and the molecules are linked by N—H…O and C—H…O hydrogen bonds to form ribbons. Comparisons are made with some related structures, indicating that a hydrogen‐bonded R₂²(10) ring is the common structural motif.     

2,2′‐Bi(9,9‐di‐n‐propyl­fluorene)

The central part of the title mol­ecule, C₃₈H₄₂, is planar, all the rings being in the same plane; the lateral chains (excluding H atoms) are also planar, with each pair almost perpendicular to the ring plane. In the dimer, the two alkyl‐substituted fluorene moieties are head‐to‐foot. The mol­ecule is on a special position of the space group, a centre of symmetry.     

Structure and thermochromic solid-state phase transition of poly (3-alkylthiophene)

In order to clarify the structural changes that occur in the thermochromic phase transition of poly (3-dodecylthiophene) [P3DT] and poly (3-hexylthiophene) [P3HT], the temperature dependence of x-ray diffraction and Fourier transform infrared spectra was measured. (1) Orthogonal unit-cell parameters were determined at room temperature: a=25.83 Å, b=7.75 Å, c (fiber axis)=7.77 Å for P3DT and a=16.63 Å, b=7.75 Å, and c=7.77 Å for P3HT. A large variation of the a-axis length between P3DT and P3HT indicates the extended trans conformation for the alkyl side chains which are oriented along the lateral a-axis direction. (2) The interplanar spacing, intensity, and integral width of the x-ray (h00) and (00l) reflections were found to change drastically in the transition region. (3) Polarized infrared measurements at high temperature revealed a marked increase of the gauche band intensity for the alkyl side group modes followed by a decrease in the band intensity of the thiophene ring modes. (4) The layer reflections of the x-ray fiber diagram become diffuse at high temperatures, indicating that the transition occurs in a liquidcrystalline manner with the orientation of the main chain axes preserved but with almost no axial correlation between the neighboring main chains. These results provide experimental support for the structural model proposed earlier: as the temperature increases, the trans-type side chains begin to disorder by introduction of gauche bonds. This disordering disrupts the regularity of the main chain conformation and decreases the effective length of the polythiophene conjugated system.     

Factors influencing the electroreductive polymerization of di‐n‐hexyldichlorosilane

This paper reports the study of the effects of solvent, support electrolyte and the nature of the electrodes on the electroreduction of di‐n‐hexyldichlorosilane. The work performed involved the use of different types of sacrificial anode (magnesium, aluminium and zinc) and cathode (magnesium, aluminium, zinc, stainless steel, nickel, carbon and palladium) in tetrahydrofuran containing lithium perchlorate (LiClO₄). Monomodal poly(di‐n‐hexyldichlorosilane) was obtained with Al/Al and Mg/Mg electrode pairs, but the polymer yield was about ten times higher with Al/Al (11%) than with Mg/Mg (1%). From the solvents and co‐solvents used (tetrahydrofuran, hexamethylphosphorotriamide, acetone, hexane, toluene, 1,1,3,3‐tetramethylurea, tris(3,6‐dioxaheptyl)amine, 1,2‐dimethoxyethane, N,N‐dimethylacetamide and dimethylformamide) with LiClO₄, only the system tetrahydrofuran + hexamethylphosphorotriamide, tetrahydrofuran + N,N‐dimethylacetamide and tetrahydrofuran + toluene have given monomodal poly(di‐n‐hexyldichlorosilane) using an aluminium anode and stainless‐steel cathode. Copyright © 2001 John Wiley & Sons, Ltd.     

The interplay of solvation,molecular conformation and supramolecular assembly in 1,1′‐({[(ethane‐1,2‐diyl)dioxy](1,2‐phenylene)}bis(methanylylidene))bis(thiosemicarbazide) and its N,N‐dimethylformamide disolvate

The wide diversity of applications of thiosemicarbazones and bis(thiosemicarbazones) has seen them used as anticancer and antitubercular agents, and as ligands in metal complexes designed to act as site‐specific radiopharmaceuticals. Molecules of 1,1′‐({[(ethane‐1,2‐diyl)dioxy](1,2‐phenylene)}bis(methanylylidene))bis(thiosemicarbazide) {alternative name: 2,2′‐[ethane‐1,2‐diylbis(oxy)]dibenzaldehyde bis(thiosemicarbazide)}, C₁₈H₂₀N₆O₂S₂, (I), lie across twofold rotation axes in the space group C2/c, with an O—C—C—O torsion angle of −59.62 (13)° and a trans‐planar arrangement of the thiosemicarbazide fragments relative to the adjacent aryl rings. The molecules of (I) are linked by N—H...S hydrogen bonds to form sheets containing R²₄(38) rings and two types of R²₂(8) ring. In the N,N‐dimethylformamide disolvate, C₁₈H₂₀N₆O₂S₂·2C₃H₇NO, (II), the independent molecular components all lie in general positions, but one of the solvent molecules is disordered over two sets of atomic sites having occupancies of 0.839 (3) and 0.161 (3). The O—C—C—O torsion angle in the ArOCH₂CH₂OAr component is −75.91 (14)° and the independent thiosemicarbazide fragments both adopt a cis‐planar arrangement relative to the adjacent aryl rings. The ArOCH₂CH₂OAr components in (II) are linked by N—H...S hydrogen bonds to form deeply puckered sheets containing R²₂(8), R²₄(8) and two types of R²₂(38) rings, and which contain cavities which accommodate all of the solvent molecules in the interior of the sheets. Comparisons are made with some related compounds.     

Dual‐emissive polydiphenylsilane nanocomposite: effect of N,N′‐bis(4‐hydroxysalicylidene)‐1,2‐phenylenediamine‐Zn complex

The fluorescence properties of polysilane can be strongly influenced by creating new excited states that involve electronic transitions and the relaxation to the ground state. This work presents the optical effects obtained by doping a specially designed polydiphenylsilane copolymer with Zn complex of N,N′‐bis(4‐hydroxysalicylidene)‐1,2‐phenylenediamine. The nanocomposites have been prepared in solution by mixing the polymer with low amounts of Zn–salophen and using tetrahydrofuran as solvent. The ultraviolet–visible spectrum has shown the occurrence of an intermolecular charge transfer between polysilane and the metal complex. Photoluminescence studies have revealed an interesting dual emission profile of nanocomposite. The origin of this phenomenon has been evidenced by molecular modeling and simulation of the electronic transitions. The modeling results have unveiled a new low‐lying excited state due to intermolecular interactions. The thin films of nanocomposites have been drop‐casted from solutions. The obtained films have been studied by Transmission Electron Microscopy (TEM)‐Scanning Transmission Electron Microscopy (STEM)‐Energy Dispersive X‐ray analysis (EDX) to gain information on the film‐forming capacity and surface morphology. The results have revealed a high potential of such materials for fluorescence sensing applications. Copyright © 2015 John Wiley & Sons, Ltd.