Showing papers in "Journal of Inorganic and Organometallic Polymers and Materials in 2007"

Nanoparticles in Liquid Crystals: Synthesis, Self-Assembly, Defect Formation and Potential Applications

Abstract: Revolutionary developments in the fabrication of nanosized particles have created enormous expectations in the last few years for the use of such materials in areas such as medical diagnostics and drug-delivery, and in high-tech devices. By its very nature, nanotechnology is of immense academic and industrial interest as it involves the creation and exploitation of materials with structural features in between those of atoms and bulk materials, with at least one dimension limited to between 1 and 100 nm. Most importantly, the properties of materials with nanometric dimensions are, in most instances, significantly different from those of atoms or bulk materials. Research efforts geared towards new synthetic procedures for shape and size-uniform nanoscale building blocks as well as efficient self-assembly protocols for manipulation of these building blocks into functional materials has created enormous excitement in the field of liquid crystal research. Liquid crystals (LCs) by their very nature are suitable candidates for matrix-guided synthesis and self-assembly of nanoscale materials, since the liquid crystalline state combines order and mobility at the molecular (nanoscale) level. Based on selected relevant examples, this review attempts to give a short overview of current research efforts in LC-nanoscience. The areas addressed in this review include the synthesis of nanomaterials using LCs as templates, the design of LC nanomaterials, self-assembly of nanomaterials using LC phases, defect formation in LC-nanoparticle suspensions, and potential applications. Despite the seeming diversity of these research topics, this review will make an effort to establish logical links between these different research areas.

Schiff Base Complexes in Macromolecules

Abstract: Schiff base metal complexes are a class of compounds that have been studied extensively because of their attractive chemical and physical properties, and their wide-ranging applications in numerous scientific areas. Researchers have incorporated Schiff base complexes into polymers, generating new materials with useful mechanical, thermal, chemical, and electronic properties. This work comprehensively reviews the developments in macromolecules containing Schiff base metal complexes, emphasizing new synthetic strategies and characterization techniques that were used to prepare and study these polymers.

In Vitro and In Vivo Characterization of Biodegradable Poly(organophosphazenes) for Biomedical Applications

Abstract: The need and the growing interest in polymers as biomaterials have led to the synthesis of new polymers with a variety of physico-chemical properties. Biomedical application of such materials not only depends on their physical properties but also on biocompatibility and biodegradability. Polyphosphazenes are a family of ‘hybrid inorganic–organic polymers’ with inorganic elements in the backbone and organic side-groups. The polyphosphazenes constitute a family of greatly diverse performance materials with a broad spectrum of properties. The present review focuses on the biodegradable polyphosphazenes, their biocompatibility, and degradation behavior both in vitro and in vivo. This review also covers the use of biodegradable polyphosphazenes as controlled release devices.

Metallo-supramolecular polymerization: A route to easy-to-process organic/inorganic hybrid materials

Abstract: The self-assembly polymerization of ditopic macromolecules via metal–ligand binding is a facile route for the preparation of metallo-supramolecular polymers (MSPs). We herein review our recent work focused on the synthesis and investigation of metallo-supramolecular polymers based on 2,6-bis(1′-methylbenzimidazolyl)pyridine endcapped poly(p-phenylene ethynylene) and poly(p-xylene) macromonomers. These materials are readily solution-processable and display appreciable mechanical properties as well as other attractive properties such as specific opto/electrical functions or high thermal stability. Our work illustrates that metallosupramolecular polymerization offers an attractive approach to assemble high-molecular-weight macromolecules from well-defined, easy to process precursors. Variation of the ditopic ligands and metal ions allows one to easily tailor the desired properties.

A Perspective of Polyphosphazene Research

Abstract: The development of polyphosphazene science and technology is traced from its beginnings in the 1960’s to the present day, with a focus on synthesis methods, model compound research, and evolving studies in biomedicine, photonics, energy storage and generation, and aerospace materials. Emphasis is placed on understanding the relationship between molecular structure and properties and drawing lessons from this research that may apply to the challenges of the future.

Ionic Conductivity of Cross-linked Polymethacrylate Derivatives/Cyclophosphazenes/Li+ Salt Complexes

Abstract: The role of cyclophosphazenes with oxyethylene chains (N3P3(OCH2CH2)nOCH3, (n = 3, 3, n = 7.2, 4) and N4P4[OC6H4O(CH2CH2O)7.2CH3]8 (8) for the synthesis and ionic conductivity in polymethacrylate networks was studied. Reflecting the structural features of cyclophosphazenes, the 7Li NMR spectra of the mixture of 3 and LiN(SO2CF3)2 showed that more than 40% of the Li+ salt could exist as a free ion at room temperature. Similar values were obtained for 4 and 8. Cross-linked methacrylate polymers (12–14, and 16–18) were prepared from the reaction of poly(ethylene glycol) methyl ether methacrylate and poly(ethylene glycol) dimethacrylate both in the presence of these cyclophosphazenes which act as molecular imprinting molecules (method II, M-II) and without the cyclophosphazene (method I) DSC studies of the imprinted polymer, 12(20)/3/Li+ system after removal of the cyclophosphazene showed that the glass transition temperature range (ΔTg) becomes significantly narrower compared to that of the unimprinted 11(20)/3/Li+ system, where cross-linked polymer 11(20) was prepared in the absence of the cyclophosphazenes (method I, M-I). The ionic conductivity of the Li+/cross-linked polymer system was improved by the subsequent readdition of the cyclophosphazenes. The 12(20)/3/Li+ complex showed a conductivity of 1.1 × 10−3 S/cm at 90 °C, which was two times higher than that of the 11(20)/3/Li+ complex. The effectiveness of the small molecule imprinting technique for the preparation of cross-linked polyelectrolytes with high conductivity and mechanical stability is discussed.

Vapochromism and Crystallization-Enhanced Emission of 1,1-Disubstituted 2,3,4,5-Tetraphenylsiloles

Abstract: Effects of solvent vapor on the photoluminescence (PL) of 2,3,4,5-tetraphenylsiloles carrying different 1,1-substituents [(PhC)4SiRR′, R = Ph, R′ = CH3 (2); R = Ph, R′ = C≡CH (3); R = R′ = C≡CH (4)] were investigated. The emission of the silole spots on the TLC plates can be turned “off” and “on” continuously and reversibly by wetting by, and de-wetting from, vapors of organic solvents, respectively. After fumigation by solvent vapor, the thin film of 4 coated on the quartz substrate emits stronger and bluer PL owing to the transformation of film morphology from the amorphous to the crystalline phase. Analysis by X-ray diffraction reveals that the molecular conformations of the crystals of 2–4 are locked and stabilized by multiple C–H···π hydrogen bonds. This structural rigidification has made the silole crystals stronger emitters.

Synthesis, Structural Characterization, and Ability to Inhibit Cancer Growth of a Series of Organotin Poly(ethylene glycols)

Abstract: A series of organotin poly(ethylene glycols) were synthesized including the first water soluble organotin polymers. These products are all polymeric with weight average molecular weights about 105. Infrared spectroscopy shows the presence of moieties from both reactants and the formation of the Sn–O linkage. F MALDI MS shows the presence of up to over a hundred units and by isotopic abundance the presence of one, two, and three tin-containing ion fragments. The polymers inhibit the growth of cancer cell lines from bone, prostate, colon, breast, and lung cancers. In a number of instances chemotherapeutic index values of two and greater are found consistent with these polymers being more active against cancer cells than non-cancerous healthy cells. Thus, some of these polymers show good promise as a new family of anticancer drugs including the water-soluble organotin-containing polymers.

Water-Soluble Polyphosphazenes for Biomedical Applications

Abstract: Water-soluble polyphosphazenes are an emerging class of biologically important synthetic polymers. Rapid advancements in the field have been facilitated with the discovery of potent polyphosphazene immunoadjuvants, use of hydrophilic polyphosphazenes in mild microencapsulation processes, and synthesis of water-soluble biodegradable polyphosphazenes – analogs of the well known pharmaceutical carriers. Present review summarizes the most recent advances in the synthesis of water-soluble polyphosphazenes, studies on their degradation and biological performance.

Synthesis, Structure and Thermal Properties of Copper and Silver Polyynides and Acetylides

Abstract: Polyynes or oligoynes having general formula H–(C≡C)n–H with n = 1,2,3,4,…, are a class of molecules that has become easily accessible in recent years due to new synthetic approaches. These molecules form copper and silver salts, which have been called, respectively, Cu-polyynides and Ag-polyynides. Here we show the synthesis of these salts and discuss their FT-IR spectra and thermal behaviour, which is studied by Differential Scanning Calorimetry (DSC). These properties are compared to the spectra and thermal behaviour of Cu2C2 and Ag2C2. It is shown that Cu2C2 can be oxidized to Cu-polyynides thereby loosing its original structure and becoming a polymeric coordinative structure. The structural changes make Cu-polyynides no more explosive than the parent Cu2C2. Similarly, Ag-polyynides, which decompose exothermally when heated, are not explosive compared to Ag2C2. The explosive decomposition of Cu2C2 occurs at 127 °C (DSC) whereas Ag2C2 decomposes explosively at 169 °C under the same conditions. Conversely, Cu-polyynides, when heated in the DSC, show a broad exothermal peak at about 243 °C. Ag-polyynides decompose near 94 °C and the release of energy is sufficiently gradual that no explosion is detected.

Oligomer and Polymer Formation in Hexamethylcyclotrisiloxane (D3) – Hydrosilane Systems Under Catalysis by tris(pentafluorophenyl)borane

Abstract: Reactions of hexamethylcyclotrisiloxane, D3, with 1,1,3,3-tetramethyldisiloxane, HMMH, 1,1,1,3,3-pentamethyldisiloxane, HMM, phenyldimethylsilane and phenylmethylsilane catalyzed by tris(pentafluorophenyl)borane were studied. These reactions lead to ring opening of D3 by the SiH reactant producing open chain oligomers with hydrosilane functionality at one or both chain ends. The reactivity of the hydrosilanes toward D3 decreases in the series: PhMeSiH2 > HMMH > PhMe2SiH > HMM. Competitive self-oligomerization of HMMH and HMM also occurs. Primary products of these processes are able to enter into reactions with the SiH and D3 reactants; some also undergo cyclization. Thus, consecutive and competitive processes lead to a series of various oligohomologues. Gas chromatography in conjunction with chemical ionization mass spectroscopy permitted identification of structure and determination of the basic directions of these oligomerization processes. Polysiloxanes of higher molecular weight may be also formed in some of these systems. The reactions, which occur in the systems studied, are rationalized on the basis of the mechanism involving the hydride transfer from silicon to trivalent boron. This includes the transient formation of tertiary trisilyloxonium borate which decomposes by the hydride transfer to one of the silicon atoms of the trisilyloxonium center.

New approaches to hybrid polymers that contain phosphazene rings

Abstract: New methods are described for the incorporation of cyclophosphazene rings into macromolecules. These include polynorbornenes with cyclophosphazene side units produced by ROMP reactions, polystyrenes linked to phosphazene rings by azide coupling processes, and cyclolinear polymers by ADMET and Heck coupling reactions. These last species are wavelength-emission tailored electroluminescent materials.

The Biocompatibility of Biodegradable Glycine Containing Polyphosphazenes: A Comparative study in Bone

Abstract: Polyphosphazenes have gained considerable attention as biomaterials for use in tissue engineering and orthopaedic reconstruction. In this paper we examined the polyphosphazenes’ in vivo biocompatibility and degradation by studying their ability to repair bone in a rabbit metaphyseal distal femur defect model. Matrices constructed from poly[(50% p-methylphenoxy)-(50%ethyl glycinato) phosphazene] (PPHOS-50) and poly[bis(ethyl glycinato) phosphazene] (PPHOS-100), were surgically implanted into a metaphyseal rabbit defect of the distal femur as constructs for tissue regeneration. Poly(lactide-co-glycolide) (PLAGA) implants, which are the biodegradable polymers most widely used clinically, and defects without polymers were used as controls in this experiment. Histological studies demonstrated that both PPHOS-50 and PPHOS-100 appeared to support bone growth comparable to the control PLAGA. By 12 weeks, femurs with polyphosphazene implants showed evidence of bone in-growth and a mild fibrous response. The PPHOS-50 implants were found to have a local tissue response that was more favorable than PPHOS-100 and similar to PLAGA. Biodegradable polyphosphazenes are a novel class of polymers which have been observed to facilitate bone growth in vivo.

Phenolic Resin/Octa(aminophenyl)-T8-Polyhedral Oligomeric Silsesquioxane (POSS) Hybrid Nanocomposites: Synthesis, Morphology, Thermal and Mechanical Properties

Abstract: Octa(aminophenyl)-T8-polyhedral silsesquioxane, 1, can serve as a cross-linking agent for organic polymeric resins. Amino functional groups of 1 can form chemical bonds or hydrogen-bonds to appropriate matrix polymers or resins. Various resole phenolic resin/1 nanocomposites (0, 1, 3, 6, and 12 wt% 1) were prepared. Hydrogen bonding between phenolic hydroxyls and the amino groups of 1 in these nanocomposites were investigated by FT-IR. The aggregation morphologies of 1 within these samples were examined using SEM, TEM, and Wide Angle X-ray Diffraction (WAXD) studies. Small quasispherical nanometer-sized POSS particles which were further aggregated into clusters, like individual grapes in a bunch, formed into phase-separated domains as large as 400 nm in diameter as the loading of 1 increased. These particles exhibited a broad 2θ = 5.8° WAXD peak indicating the presence of some crystalline order within the nanoparticles of 1 making up the aggregates. This corresponds to an average crystalline plane lattice distance of 17.5 A. However, extraction of the finely powdered nanocomposites by refluxing THF failed to remove 1 indicating the vast majority of 1 must be chemically bound. Thus, the aggregates must have resin within their structure. The storage modulus (E') in both the glassy and rubbery regions, thermal stability, and glass transition temperature of the composites were improved by 1 wt% 1. However, at high loadings of 1, these properties gradually decreased. Surface extractions by THF removed only a portion of the 1 in the surface regions based on X-EDS analyses for Si, suggesting that a portion of 1 might chemically bond into the phenolic resin matrix during the cure. As the loading of 1 increased, the content of 1 at specific surface locations gradually tends to increase and confirmed excellent dispersion of 1 in the micron size-scale at all locations.

Antibacterial Thin Films on Glass Substrate by Sol–Gel Process

Abstract: Submitted June 16, 2006; Accepted October 16, 2006 Antibacterial transparent thin films, containing different amounts of silver ion, have been prepared on a glass substrate by the sol–gel process. Thin films were obtained from inorganicorganic hybrid sols derived from 3-(glicydiloxypropyl)trimethoxy silane, N-(2-aminoethyl)3-aminopropyl-trimethoxysilane and aluminium-sec-butoxide/ethylaceto-acetate complex and doped with silver ions. The films were characterized by Scanning Electron Microscopy and Raman Spectroscopy. The physical properties of the films were studied by solar-box, taber abraser, hardness test pencil, scratch-adhesion test and spectroscopy. The antibacterial activity of the coatings were investigated against gram negative Escherichia coli and gram positive Staphylococcus aureus. The results showed that 1% doping of the transparent hybrid thin film with silver ions resulted in high antibacterial properties of the film.

Synthesis, Structural Characterization, and Initial Evaluation as Anticancer Drugs of Dibutyltin Polyamines Derived from Various 4,6-Diaminopyrimidines

Abstract: A number of diaminopyrimidines have been incorporated into dibutyltin polyamines with molecular weights ranging from 3.5 × 104 to 3.7 × 106 and product yields from 47 to 88%. Infrared spectroscopy is consistent with the inclusion of the diaminopyridines into the polymer backbone with the IR spectroscopy showing the formation of the Sn–N bond as well as the presence of bands from both reactants being present in the polymer. F MALDI MS is also consistent with the products being polymeric and containing units from both the dibutyltin and pyrimidine reactants. The products exhibit good inhibition of cancer cell lines including those derived from human lung, bone, breast, prostrate, and colon cancers. Inhibition occurs within the same concentration range, and lower than that of the most widely employed chemotherapeutic drug, cisplatin.

Gas Diffusion and Solubility in Poly(organophosphazenes): Results of Molecular Simulation Studies

Abstract: A combination of quantum chemistry, molecular dynamics, and Monte Carlo methods have been used to investigate gas diffusion and solubility in three isomeric poly[di(butoxyphosphazenes)] and in amorphous and crystalline states of poly[bis(2,2,2-trifluoroethoxyphosphazene)] (PTFEP). In this review of recently published studies reported from our laboratory, conclusions are reached in regards to the relationship between polymer structure and gas diffusion and sorption in poly(organophosphazenes). These conclusions also serve to validate our current understanding of the nature of gas transport in other polymers. Specifically, gas diffusivity has been shown to increase with increasing side-chain and main-chain mobility as determined from vectorial autocorrelation function analysis; however, high diffusivity is accompanied by a loss in diffusive selectivity resulting in decreasing permselectivity with increasing permeability. Simulation of crystalline supercells of PTFEP indicate that gas diffusion is unrestricted in the crystalline state as has been reported only for a few other polymers, principally poly(4-methyl-1-pentene). Gas solubility in poly(organophosphazenes) correlates well with gas condensability as measured by the Lennard–Jones potential well depth parameter, ɛ/k. Exceptions are cases where specific interactions can occur between gas molecules and the polymer chain such as is the case of CO2 and PTFEP. High-level ab initio calculations of the interaction of CO2 with low-molecular-weight fluoroalkanes indicate the presence of a weak quadrupole–dipole interaction. Association of CO2 with the trifluoromethyl groups of the trifluoroethoxy side chain of PTFEP has been confirmed by radial distribution function (RDF) analysis of MD trajectories. Comparison between solubility coefficients obtained from Grand Canonical Monte Carlo (GCMC) simulations of amorphous cells with experimental values of microcrystalline PTFEP indicates that gas solubility in polyphosphazenes such as PTFEP that exhibit a mesophase/crystalline state is greatly reduced.

Quaternary Ammonium Salts (QAS) Modified Polysiloxane Biocide Supported on Silica Materials

Abstract: Three types of silica particles modified with vinyl groups were obtained: (i) xerogel formed by hydrolytic polycondensation of the mixture of tetramethoxysilane (TMOS) and 1,1,1,7−tetramethoxy-3,5,7-trimethyl-3,5,7-trivinyltetrasiloxane, (ii) mesoporous silica obtained from the same precursors in the presence of the cetyltrimethylammonium bromide (CTAB), and (iii) commercial Fluka silica gel 60A with a vinyltriethoxysilane-treated surface. Vinyl groups on these silica materials were transformed into silyl chloride by hydrosilylation with HMe2SiCl. These groups were used to graft living polysiloxane that was synthesized by anionic ring-opening polymerization of 2,4,6-tri(3-chloropropyl)-2,4,6-trimethylcyclotrisiloxane and initiated by BuLi. Chloropropyl groups on the grafted polymer were used to quaternize N,N-dimethyl-n-octylamine. Silica particles with grafted polysiloxane having quaternary ammonium salt (QAS) groups pendant to polymer chains were obtained. Silica material with QAS groups directly attached to the surface were generated by the action of N,N-dimethyl-n-octylamine on particles obtained by the sol–gel process involving tetraethoxysilane (TEOS) with 3-chloropropyltriethoxysilane. The bacteriocidal properties of all these materials were tested in water suspension against five representative strains for Gram-positive and Gram-negative bacteria. Some of the silica–polysiloxane hybrid materials have good antibacterial properties against Gram-positive strains, but not as good as the non-tethered QAS-substituted polysiloxane in water solution. The QAS groups that are directly bonded to the silica material surface are inactive.

Synthesis, Optical Properties, and Photoluminescence of Organometallic Acetylide Polymers of Platinum Functionalized with Si and Ge-Bridged Bis(3,6-Diethynyl-9-butylcarbazole)

Abstract: A series of light-emitting group 14 element-containing organometallic platinum polyynes of the form trans-[–Pt(PBu3)2C≡ CArC≡ C(ER2)C≡ CArC≡ C–] n (Ar = 9-butylcarbazole-3,6-diyl, ER2 = SiMe2, SiPh2, GeMe2, GePh2) were synthesized and spectroscopically characterized. The solution properties and regiochemical structures of this new structural class of organosilicon- and organogermanium-based metallopolyynes were studied by IR and NMR (1H, 13C, 29Si, and 31P) spectroscopies. The optical absorption and photoluminescence spectra of these metallopolymers were examined and compared with their well-defined dinuclear model complexes trans-[Pt(Ph)(PEt3)2C≡ CArC≡ C(ER2)C≡ CArC≡ CPt(Ph)(PEt3)2]. The influence of the heavy platinum atom and the group 14 silyl or germyl structural unit possessing different side group substituents on the thermal and phosphorescence properties were investigated in detail. We have also established the goal for studying the evolution of the lowest singlet and triplet excited states with the nature of ER2 unit in these metallopolymers. The present work indicates that the phosphorescence emission efficiency harnessed through the heavy-atom effect of platinum in the main chain changes significantly with the identity of ER2 in the general orders GeR2 > SiR2 (R = Me, Ph) and EMe2 > EPh2 (E = Si, Ge).

Synthesis and Characterization of Ceramic Precursor Aluminum-Containing Polycarbosilane and its Pyrolysis

Abstract: The aluminum-containing polycarbosilane (Al-PCS) was synthesized by reaction of an aluminum alkoxide with polycarbosilane (PCS). The Al-PCS product was characterized by element analysis, gel permeation chromatography (GPC), as well as Fourier transform (FT-IR) and nuclear magnetic resonance (1H, 29Si, 13C, and 27Al NMR) spectroscopy. The results show that Al-PCS is very similar to PCS in structure. This preceramic precursor is described as a dispersion of Al(AcAc)3-based particles in the PCS chain matrix. The pyrolysis process of Al-PCS was investigated by thermogravimetry (TG), FT-IR, and X-ray diffraction (XRD). The pyrolysis of Al-PCS includes three sequential stages: First, the condensation and thermal decomposition into the inorganic state; second, the transition toward the third stage involving the thermal decomposition of the side chains into an amorphous state; third, the crystallization of β-SiC.

Recent Advances in Organometallic Polymers as Highly Efficient Electrophosphorescent Emitters

Abstract: Recent progress and development of organometallic electrophosphorescent polymers, which attracted increasing interest of researchers in the field of phosphorescent light-emitting devices, has been reviewed The synthesis, structural characterization, photoluminescence, electroluminescence and possible application of electrophosphorescent polymers are surveyed and discussed

Synthesis of Ferrocene-containing Polyacetylenes by Click Chemistry

Abstract: Ferrocene-containing polyacetylenes are synthesized in good yields by Cu-catalyzed click reactions of azido moieties of poly[(6-chloro-1-phenyl-1-hexyne)-co-(6-azido-1-phenyl-1-hexyne)] and poly{1-[(4-azidohexyloxy)phenyl]-2-phenylacetylene} with ethynylferrocene. All the organometallic polymers are completely soluble in common organic solvents such as chloroform, THF and toluene. Spectroscopic analyses reveal that all the azido functional groups have cyclized with ethynylferrocene. With the incorporation of ferrocene rings into the polyacetylene structure, the resulting polymers show enhanced thermal stability and redox activity.

Electrostatic Assembly with Poly(ferrocenylsilanes)

Abstract: New frontiers in polymer science involve the incorporation of functional species into material systems. The electrostatic layer-by-layer (LBL) self-assembly technique constitutes a versatile tool for nano- and microscale fabrication of devices and novel material structures. Although a rapidly growing attention has been paid to this area, most of the studies conducted were based on organic polymeric electrolytes. Due to synthetic developments, new polymeric structures with inorganic elements and transition metals incorporated in the main chain have become accessible. With the development of new synthesis routes, organometallic poly(ferrocenylsilane) polycations and polyanions emerged. Their charged nature and water-solubility made them excellent candidates for the extension of electrostatic multilayer assembly to organometallic polymeric materials. The present review gives a concise summary on the LBL fabrication of organometallic thin films and microcapsules based on water-soluble poly(ferrocenylsilane) polyions. The unique functions of these structures come from the molecular structure of poly(ferrocenylsilanes), in which silicon atoms and redox-active ferrocene units are present. In this context, the diverse application potentials of these organometallic multilayer structures are also discussed

Ferrocene-containing Liquid Crystalline Polymers

Abstract: This article is one of a number of reviews in a special issue to honor Prof. Dr. Ian Manners of the University of Bristol, UK, for his outstanding contributions in the field of organometallic polymers. The focus of this review is on the syntheses, properties, and characterization of ferrocene-containing liquid crystalline polymers in which ferrocene moieties are in or pendent to the backbone and also dendrimers and [60]fullerene-ferrocene liquid crystalline materials.

Factors Controlling the Rate of Photodegradation in Polymers: The Effect of Temperature on the Photodegradation Quantum Yield in a PVC Polymer Containing Metal–Metal Bonds in the Polymer Chain

Abstract: The effect of temperature on the degradation quantum yield of a poly(vinyl chloride) polymer with Cp2Mo2(CO)6 units incorporated into its chains was studied (Cp = cyclopentadienyl). The polymer is photochemically reactive in the absence of oxygen because the CpMo(CO)3 radicals formed by photolysis of the Mo–Mo bonds react with C–Cl bonds to form CpMo(CO)3Cl units. Quantum yields as a function of temperature were obtained for this polymer and for two control systems, Cp′2Mo2(CO)6 dispersed in PVC and Cp′2Mo2(CO)6 in hexane/CCl4 solution (Cp′ = η5-C5H4CH3). The quantum yields of the two control systems showed only slight increases with an increase in temperature. For the reaction in hexane/CCl4, this temperature dependence is attributed to the decrease in viscosity of the solution and the subsequent decrease in the radical-radical recombination efficiency. For the Cp′2Mo2(CO)6 dispersed in PVC, the small temperature dependence is attributed to an increase in free volume as the temperature increases. In contrast to these results, the temperature dependence of the quantum yield of the PVC polymer with Cp2Mo2(CO)6 units along its chains is relatively large. It is proposed that an increase in temperature facilitates the polymer chain relaxation processes (involving recoil and rotation) following photolysis of the Mo–Mo bond. The radical–radical recombination efficiency is subsequently decreased, which leads to a net increase in chain cleavage and degradation efficiency.

Self-Recognition of 3D Porous Frameworks: Fourfold Diamondoid or Threefold Cuboidal Interpenetrating Nets Formed by Varying Pillar Motifs

Abstract: Compound [Ni(2,6-ndc)(bpe)(H2O)] n (1) was prepared by the hydrothermal reaction of 2,6-naphthalenedicarboxylic acid (2,6-H2ndc) and trans-1,2-bis(4-pyridyl)ethylene (bpe) with Ni(NO3)2·6H2O under alkaline (NaOH) conditions. Treatment of 2,6-H2ndc, 4,4′-bipyridine (4,4′-bpy) with M(NO3)2·6H2O (M = Ni or Co) under similar conditions afforded compounds [Ni2(2,6-ndc)2(4,4′-bpy)] n (2) and [Co2(2,6-ndc)2(4,4′-bpy)] n (3), respectively. A single-crystal X-ray diffraction study revealed that compound 1 adopts a 3D fourfold interpenetrating diamondoid network stabilized by inter-net OH···O hydrogen bonds. The anionic 2,6-ndc ligand presents two different bonding characteristics, bis(monodentate) and bis(chelating bidentate) modes. A solid-state structural analysis revealed that compounds 2 and 3 are isomorphous and isostructural. Both present a 3D threefold interpenetrating cuboidal framework, consisting of a 2D (4,4)-net of interconnected [M 2(O2C)4] (M = Ni, Co) paddle-wheel dinuclear units, and pillared by 4,4′-bpy ligands. The degree of interpenetration of these compounds could be adjusted successfully by varying only the organic pillar motifs.

Formation of Polymeric Lewis Acid–Lewis Base Complexes with Well-defined Organoboron Polymers

Abstract: The binding of Lewis bases to organoboron polymeric Lewis acids has been studied and the parameters that determine the complexation equilibrium have been investigated, which include (i) the strength of the individual Lewis acids and Lewis bases, (ii) concentration, and (iii) temperature. While the strongly Lewis acidic borane polymers poly(4-bis(pentafluorophenyl)borylstyrene) (PS-BPf) and poly(4-(di-2-thienylboryl)styrene) (PS-BTh) form isolable complexes with strong Lewis bases such as 4-t-butylpyridine (tPy), a temperature dependent equilibrium is established with weaker bases such as THF. Similarly, the weakly Lewis acidic boronate polymer poly(4-diethoxyborylstyrene) (PS-BOEt) undergoes a temperature dependent equilibrium with the strong Lewis base 4-dimethylaminopyridine (DMAP), while poly(4-pinacolatoborylstyrene) (PS-BPin) does not significantly bind to pyridine bases. Decomplexation of PS-BTh· t Py is achieved by treatment with the stronger Lewis acid, B(C6F5)3, thereby confirming the reversible nature of the polymeric Lewis acid–base adducts.

New Preparation and Purification Methods for Metallo-Supramolecular Block Copolymers

Abstract: The bis-complex formation of two terpyridine-modified polymers using microwave assisted reaction conditions was investigated in detail. In order to construct a heteroleptic block copolymer polystyrene, which was prepared by nitroxide-mediated radical polymerization (NMRP), and a commercial available poly(ethylene oxide) were used. These studies include the influence of temperature, reaction time, concentration and the use of different solvent mixtures on complexation. The conversion was determined by GPC measurements. The amphiphilic metallo-supramolecular block copolymers were investigated towards their formation of micellar aggregates in water. Other characterization techniques include 1H-NMR, UV/vis spectroscopy, dynamic light scattering (DLS), atomic force spectroscopy (AFM) and transmission electron microscopy (TEM) techniques.

Elastomeric properties of polysiloxane networks: birefringence measurements on bimodal elastomers that are presumed to be spatially inhomogeneous

Abstract: In-situ measurements of birefringence during simple extension were performed on a series of end-linked bimodal poly(dimethylsiloxane) elastomers that were templated to possess high cross-link density nanostructures. The strain birefringence showed marked deviations from predictions of linearized Gaussian rubber-like elasticity theory for a bimodal elastomer with well-developed structure (nanoscale to microscale). However, the stress-birefringence relation for this same network seemed to be described by Gaussian rubber-like elasticity theory. Reinforced bimodal networks that were macroscopically homogenous (although potentially possessing nanoscale structure) were observed to have strain birefringence scaling similar to theoretical predictions, although the magnitude was below the Gaussian prediction. Analysis of the strain birefringence shows that a non-linear, non-Gaussian effect (likely limited chain extensibility) can occur. However, in all cases the birefringence was found to have a significant linear regime over a large range of strains which suggests that limited chain extensibility may not be the sole contributor towards the well known “bimodal” reinforcement.

Transamination Reactivity of Ti(NMe 2 ) 4 and Zr(NMe 2 ) 4 with 1,3,4,5,6-Pentamethyl-2-aminoborazine and Aryl Amines. Model Chemistry for the Formation of Metalloborazine Preceramic Polymers and MN/BN (M = Ti, Zr) Ceramic Composites

Abstract: The transamination reactions between Ti(NMe2)4 and 1,3,4,5,6-pentamethyl-2-aminoborazine, (Me)3N3(Me)2B3(NH2), and diphenylamine (Ph2NH) and between [Zr(NMe2)4]2 and 1,3,4,5,6-pentamethyl-2-aminoborazine, aniline (PhNH2) and diphenylamine have been studied and the molecular product species have been isolated, spectroscopically characterized and single crystal X-ray structure analyses completed. The results of these studies have been used to interpret the outcome of reactions of Ti(NMe2)4 and Zr(NMe2)4 with borazinylamine preceramic polymers that, upon pyrolysis, produce TiN/BN, ZrN/BN and ZrH0.6N/BN composite powders.