Triazine-cored dendritic molecules containing multiple o-carborane clusters

A series of C₃-symmetricaltriazine-cored small dendritic molecules containing three to nine peripheral o-carborane clusters were synthesized through Cu(I)-catalyzedazide–alkyne cycloaddition reactions. The newly synthesized molecules containing multiple o-carborane moieties were characterized using nuclear magnetic resonance and matrix-assisted laser desorption/ionization-time of flight mass spectral analysis. The biological evaluation of these three to nine cage dendrimers was performed using breast cancer cells (Michigan Cancer Foundation 7). All these dendritic compounds showed cytotoxicity toward breast cancer cells, and the toxicity increased as the number of peripheral o-carboranes increased. The 9-cage molecule showed the highest cytotoxicity, and the half maximal inhibitory concentration (IC₅₀) value was found to be 80.67 ng/ml. Its cytotoxicity was significantly higher than the common chemotherapy agent cisplatin. As expected, the boron-richo-carborane-appended molecules showed high thermal stability. The thermal stability increased as the number of peripheral o-carborane moieties increased.     

Thermal and thermo-oxidative stabilities of some poly(siloxane-azomethine)s

Thermal and thermo-oxidative stability of some poly(siloxane-azomethine)s obtaining starting from bis(formyl-p-phenoxymethyl)tetramethyldisiloxane and different organic diamines have been investigated by TG+DTG+DSC simultaneous analyses performed in argon flow and air static atmosphere, respectively. TG, DTG and DSC curves of each polymer showed three or four successive degradation steps at different temperatures according to the composition of the sample and the gaseous atmosphere in which the thermal analysis was performed. For each process, the following parameters were evaluated: total mass loss, temperature corresponding to the maximum reaction rate, maximum reaction rate, temperature corresponding to certain mass loss. In order to determine the thermal and thermo-oxidative stabilities of investigated polymers, the following values were determined: T _x% — temperature corresponding to x% mass loss, and %Δm _T — mass loss at a given temperature T. The obtained orders of stability were correlated with the structure of investigated polymers.     

Carborane polymers. IV. Polysiloxanes

Carboranes attached to silicon through straight-chain alkyl groups were prepared and characterized for thermal stability by TGA and molecular weight change on heating. The monomers for these polymers were prepared generally by platinum-catalyzed addition of a silylhydride to an alkenyl or dialkenyl carborane. Polymerization was effected by hydrolysis-condensation of chlorosilanes, ring opening of cyclosiloxanes, and condensation of alkoxy and chlorosilanes. Two types of polymer structures were prepared, one contained m-carborane in the chain backbone, the other contained o-carborane as pendant alkylcarborane groups. Both types were obtained as elastomers; however, higher proportions of carborane in the polymers reduced elasticity and finally resulted in nonelastomers. TGA of the backbone carborane siloxane polymer indicated degradation at 370°C. in nitrogen and at 235°C. in air. Chain scission, as determined by molecular weight decrease, was observed on heating in nitrogen at 350°C. TGA of the pendant carborane siloxane polymer indicated that degradation in nitrogen and in air occurred at greater than 400°C. However, chain scission, as determined by molecular weight decrease, was observed upon heating at 300°C. in nitrogen.     

Thermal behavior of poly-p-xylylene-m-carborane

Thermal analysis, infrared spectroscopy, and gel-permeation chromatography studies were undertaken to determine the behavior of poly(p-xylylene-m-carborane) at elevated temperature. Results show that the polymer softened at about 200°C, probably because of polymorphism. Chlorine atoms from chain ends also ruptured at this temperature. This initiated subsequent hydrogen abstraction and thermal oxidation reactions that resulted in the decomposition of the polymer. The process of degradation closely parallels the thermal oxidation of polybenzyl and other polymers with readily activated methylene groups. The volatile products that formed at 300 and 400°C were produced because of the cleavage of methylene groups and their oxidation products. Larger polymer segments containing phenylene and m-carborane groups were evolved at higher temperatures. Some crosslinking occurred when the polymer was heated in air at temperatures above 200°C. The degree of polydispersity of the polymer fraction that remained soluble in organic solvents increased with corresponding increase of temperature.     

Icosahedral carboranes. XVI. Preparation of linear poly-m-carboranylenesiloxanes

The first members of the series of poly-m-carboranylenesiloxanes were synthesized by the ferric chloride-catalyzed condensation of methoxy- and chloro-terminated monomers and generally obtained as insoluble crosslinked gums It has now been discovered that long-chain, linear polymers can be prepared by simple hydrolytic condensation of m-B₁₀H₁₀C₂(SiMe₂OSiMe₂Cl)₂ and m-B₁₀H₁₀C₂(SiMe₂OSiMe₂OSiMe₂Cl)₂ at ice bath temperature, as well as by acid-catalyzed condensation of the corresponding silanols. In addition, phenyl-substituted copolymers have been obtained which show outstanding thermo-oxidative stability at elevated temperature. These linear polymers are soluble waxes and liquids with molecular weights between 16,000 and 30,000; they are potentially useful as high-temperature liquids and coatings and can be cured at room temperature to form elastomers.     

A new series of organoboranes. VII. The preparation of poly-m-carboranylenesiloxanes

This paper describes the preparation of the first members of a new series of polysiloxanes characterized by having m-carborane nuclei in the backbone of the polymers. Although neither hydrolysis of 1,7-bis(chlorodialkylsilyl)-m-carborane monomers nor catalytic dehydration of the corresponding dihydroxy compounds would proceed to give the type of polysiloxanes desired, the polymers were readily prepared by the ferric chloridecatalyzed elimination of an alkyl halide from equimolar mixtures of dichloro- and dialkoxysilanes. This technique allowed the systematic introduction of dialkylsiloxy groups between m-carborane nuclei. Characterization of the polymers is described as well as differential scanning calorimetry studies which show the prime members of the series to be thermally stable to 500°C. and oxidatively stable to about 350°C.     

Synthesis of (m-Carborane-9,10-diyl)diacetic Acids and Their Derivatives

(m-Carborane-9,10-diyl)diacetic acids were obtained by oxidation of 9,10-diallyl-m-carborane which, in its turn, was synthesized by palladium-catalyzed cross coupling of 9,10-diiodo-m-carborane with allylmagnesium bromide.     

Synthesis and characterization of new poly(arylene ether)s containing heterocyclic units. II.

A series of new poly(arylene ether)s, containing naphthalene, pyridine, and quinoline units have been prepared by solution condensation polymerization. The synthesis involves nucleophilic displacement of aromatic dihalides with aromatic potassium bisphenates in an anhydrous dipolar aprotic solvent at elevated temperatures. The polymers, having inherent viscosity from 0.24 to 1.32 dL/g, were obtained in quantitative yield, have excellent thermal stability as shown by 10% weight loss temperatures in nitrogen and air (above 450 and 430°C, respectively) and high glass transition temperatures (in the range of 150–220°C). The introduction of quinoline moieties in the polymer backbone positively influences the thermal properties, such as high T_g/T_m ratios. © 1995 John Wiley & Sons, Inc.     

Wholly aromatic polyamide-hydrazides. IV. Structure–property relationships for polymers containing p-phenylene and m-phenylene units

A series of wholly aromatic polyamide-hydrazides was investigated in order to acquire clear understanding of the influence exerted by controlled structural variations in these polymers upon some of important properties, such as chain flexibility, membrane permselectivity, and thermal as well as thermo-oxidative stability. For that reason, the content of para and meta phenylene units was varied within this series so that the changes in the latter were 12.5 mol % from polymer to polymer, starting from an overall content of 0–50 mol %. The polymers were prepared by a low-temperature solution polycondensation reactin of p-aminobenzhydrazide (ABH) and terephthaloyl chloride (TCI), isophthaloyl chloride (ICI), and their appropriate combinations in N,N-dimethylacetamide (DMA) as solvent and all of these preparations were monitored viscometrically in order to prepare the products with as similar as possible average molecular weights. Polymer structures were characterized by elemental analysis, infrared spectrometry, and ¹³C NMR spectroscopy, while their molecular weights were determined by light scattering and dilute-solution viscometry. Polymer properties were evaluated by solution viscometry, reverse osmosis tests, and thermal gravimetric analysis. The results obtained during the preparation of these materials, their subsequent structural characterization, and their property evaluations are discussed. They clearly indicate that substitution of m-phenylene units for p-phenylene ones within this polymer series led to an increase in polymer chain flexibility (from what is usually referred to as semiflexible or semirigid to typically flexible macromolecules), disrupted selectivity of the asymmetric thin membranes under reverse osmosis conditions and decreased stability at elevated temperatures in inert as well as in oxidative atmospheres.     

Impact of fullerenes on the thermal stability of melt processed polystyrene and poly(methyl methacrylate) composites

The impact of the two fullerenes C₆₀ and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on the thermal and thermo-oxidative stability of the corresponding melt processed composites with the two polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA), was studied using both dynamic and isothermal thermogravimetric analysis (TGA). For each polymer, three different composites with C₆₀ loadings of 1.0 wt% and 3.0 wt% and PCBM loadings of 1.0 wt% were considered. The aim of this work was to compare the stabilization effect of both fullerenes on PS and PMMA. The results obtained show unequivocally that, although PCBM has lower thermal and thermo-oxidative stability than C₆₀, the PS-PCBM and PMMA-PCBM composites have higher thermal and thermo-oxidative stability than the corresponding PS-C₆₀ and PMMA-C₆₀ composites. These results corroborate our previous reports, on showing that PCBM is better than C₆₀ at improving the thermal and thermo-oxidative stability of polymers which degrade through radical degradation mechanisms.     

Synthesis of (m-carboran-9-yl)ferrocene and (m-carboran-9-yl)cymantrene

Cross-coupling reactions of 9-iodo-m-carborane with ferrocenylzinc chloride or cymantrenylzinc chloride catalyzed by (Ph₃P)₂PdCl₂ result in the formation of (m-carbo ran-9-yl)ferrocene and (m-carboran-9-yl)cymantrene, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 542–543, March, 1998.     

D2-m-carborane-siloxanes. III. Preparation and properties of trifluoropropyl-modified polymers

Linear D₂-m-carborane-siloxanes with one, two, and three trifluoropropyl moieties per repeat unit were prepared by the condensation reaction between bisureidosilanes and carborane disilanol. Molecular weights between 100,000 and 220,000 were obtained. Compared to fluorosilicones, the trifluoropropyl-modified carborane-siloxanes exhibited greater thermal and oxidative stability and in certain cases comparable solvent resistance. The swelling index for carborane-siloxane elastomers decreased with increasing trifluoropropyl content, although this fluorocarbon moiety did compromise the thermal stability of the carborane system.     

Synthesis and radical polymerization of acrylate and methacrylate bearing an isocyanurate core with adamantyl bisurethane moieties

In this article, we report the synthesis of acrylate and methacrylate bearing an isocyanurate core with two adamantyl urethane moieties and their radical homo- and copolymerization with n-butyl methacrylate (BMA). The synthesized polyacrylate exhibits higher 5% weight loss and glass transition temperatures (T_d5 and T_g) than those of the comparative polyacrylate, synthesized from the isocyanurate-based acrylate with two hexyl urethane moieties, suggesting that the rigid adamantane core incorporated in the side chains of polymer largely contributes to increase in thermal stability of polymer. Similarly, the obtained copolymers show higher T_g values than that of homopolymer derived from BMA, leading to the synthesized monomers are useful as a comonomer to enhance thermal property of polymer.     

Solid-State Photochromism by Molecular Assembly of Bis-o-carboranyl Siloles

A new type of solid-state photochromism was observed in an AB₂-type molecular assembly comprising a central silole and two peripheral o-carborane units, and in this assembly, depending on the assembling positions of those units at the adjoining benzene ring, two different regioisomers were formed: Si-m-Cb and Si-p-Cb . Each isomer showed different solid-state photochromism depending on its solid-state molecular conformation and was either in the crystalline or amorphous state. The crystals of each meta- or para-isomer, C_Si-m-Cb or C_Si-p-Cb, showed yellow or blue emission, and mechanically grinding those crystals into amorphous powders of A_Si-m-Cb and A_Si-p-Cb, switched their emissions to blue and yellow, respectively. Photophysical studies revealed that the electronic interaction between silole and o-carborane units determined the emission color. The crystal and DFT-optimized structures each account for the crystalline and amorphous structures, respectively, and are correlated well with the electronic interactions in the molecular assembly in the solid state, thus enabling the prediction of the solid-state molecular conformational change.     

Investigation of zwitterionic 7-ammonium-7,9-nido-m-carborane

Zwitterionic ammonium-substituted nido m-carborane (7-NH₃-7,9-nido-carborane), a novel boron moiety for boron neutron capture therapy, was synthesized and its chemical properties were investigated. This boron cluster system showed unique properties by reacting with carbonyl groups of ketones and aldehydes to generate the corresponding iminium-substituted nido m-carboranes.     

Benzocyclobutene in polymer synthesis. I. Homopolymerization of bisbenzocyclobutene aromatic imides to form high-temperature resistant thermosetting resins

A series of new bisbenzocyclobutene-terminated aromatic imide monomers has been synthesized from the condensation reaction of 4-aminobenzocyclobutene and the perspective dianhydride in refluxing acetic acid/toluene. The differential scanning calorimetric studies of the foregoing monomers indicated that polymerization exotherms began at 229–250°C and reached their maxima at 258–263°C. The cured samples (250–254°C; N₂; 8 h) were surprisingly stable toward thermo-oxidative degradation; only 7–10% weight loss was observed after 200 h (in air) at 314°C (600°F). At higher temperatures (650 and 700°F), the most rigid structure was the most thermo-oxidatively stable. An approach to enhance both the final glass-transition temperature (T_g cure) and the thermo-oxidative stability of the bisbenzocyclobutene system was to dilute the cure-site density since the cure-site structure is the weakest part of the polymeric structure. Therefore, a series of bisbenzocyclobutene-terminated aromatic imide oligomers were prepared, using various aromatic amines as the chain-extending agents. Meta-phenylenediamine was apparently the most effective in the advancement of both the T_g (cure) and thermo-oxidative stability.     

9-Allyl-1,7-dicarbadodecaborane as a dienophile in aza Diels-Alder reactions of 1,2,4-triazines: synthesis of pyridines bearing a carborane cage

The synthesis of pyridine and bipyridine derivatives of m-carborane via aza Diels-Alder reaction of 1,2,4-triazines with 9-allyl m-carborane and their structural characterization and photophysical properties are described. The products 3- and 4-(m-carborane-9-ylmethyl)-2,2′-bipyridines form Zn(II) complexes on reaction with ZnCl₂, which increases significantly their fluorescence intensity.     

Catalyst‐Sidearm‐Induced Stereoselectivity Switching in Polymerization of a Racemic Lactone for Stereocomplexed Crystalline Polymer with a Circular Life Cycle

Construction of robust, stereocomplexed (sc) crystalline material, based on a recently discovered infinitely recyclable polymer system, requires blending of enantiomeric polymer chains produced from respective enantiopure, fused six‐five bicyclic lactones. Herein, the stereoselective polymerization of the racemic monomer by yttrium catalysts bearing tetradentate ligands is reported, where the tethered donor sidearm switches the heteroselectivity of the catalyst to isoselectivity when it is changed from the β‐OMe to β‐NMe₂ sidearm. The latter catalyst produces an isotactic stereoblock polymer (P_m up to 0.95) that forms the crystalline sc‐material with a T_m of up to 171 °C. This sc‐material can be fully depolymerized back to rac‐monomer in a quantitative yield and purity, thus establishing its circular life cycle.     

Structure-property relationships for novel wholly aromatic polyamide-hydrazides containing various proportions of para-phenylene and meta-phenylene units: I. Synthesis and characterization

A series of novel wholly aromatic polyamide-hydrazides was synthesized by a low temperature solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either terephthaloyl chloride (TCl), isophthaloyl chloride (ICl), or mixtures of various molar ratios of TCl and ICl in anhydrous N,N-dimethylacetamide (DMAc) as a solvent. Polymer structures were identified by elemental analysis and infrared spectroscopy. All the polymers have the same structural formula except the way of linking phenylene units inside the polymer chain. The content of para- and meta-phenylene moieties was varied within this series so that the changes in the latter were 10 mol % from polymer to polymer, starting from an overall content of 0-100 mol %. The prepared polymers were characterized for their properties in order to acquire clear understanding of the influence exerted by controlled structural variations in these polymers upon some of important properties, such as solubility, intrinsic viscosity, moisture regain, mechanical properties and thermal as well as thermo-oxidative stability. The polymers were readily soluble in several organic polar solvents such as DMAc, N,N-dimethylformamide, dimethyl sulphoxide, N-methyl-2-pyrrolidone and hexamethyl phosphoramide and could be cast into flexible films. Their solubilities were found to increase remarkably with introduction of meta-phenylene moieties into the polymer chains. Their intrinsic viscosities ranged from 0.73 to 4.83 dl g⁻¹ in DMAc at 30 °C and increased with the increase of para-phenylene units content. Mechanical properties of the films produced from these polymers are improved markedly by substitution of para-phenylene units for meta-phenylene units. Thermogravimetric studies revealed that the completely para-oriented type of polymer has better thermal and thermo-oxidative stability relative to that of the other polymers. Moreover, the results reveal that the prepared polymers have a great affinity to water sorption. The hydrophilic character increases as a function of meta-oriented phenylene rings incorporated into the polymer chains.     

Anchoring of hydrophobically modified poly(sodium acrylate)s into DDP vesicle bilayers: hydrophobic match and mismatch

 Differential scanning microcalorimetric thermograms have been recorded for aqueous solutions containing vesicles formed by sodium di-n-dodecyl phosphate, in the presence of different concentrations of poly(sodium acrylate-co-n-alkyl methacrylate), where n-alkyl= C₉H₁₉, C₁₂H₂₅, C₁₈H₃₇. The mole fraction of hydrophobic moieties in the copolymer is 0.04. The main phase transition temperature (T _m) is hardly affected by the presence of poly(sodium acrylate)s bearing n-dodecyl chains, whereas the anchoring of polymers bearing n-nonyl or n-octadecyl groups reduces the main phase transition temperature significantly from ca. 34 °C to ca. 32 °C. In parallel, the enthalpy of transition per mole of DDP monomer (Δ_m H _int) is lowered upon adding polymer. Again, the polymer containing n-dodecyl moieties hardly affects Δ_m H _int. These patterns are explained by the notion that the extent of the disruptive effect of alkyl chains incorporated into the bilayer depends on the extent of the mismatch between the chain lengths of the intruding alkyl chains and the hydrophobic moieties composing the vesicle bilayer. Added hydrophobically modified polymers increase the cooperativity of the melting process, as shown by the increase of n _DDP. We suggest that the anchoring poly(sodium acrylate-co-n-alkyl methacrylate) relieves the strain in the curved outer monolayer of a pure DDP bilayer by allowing the presence of larger “patches” characterized by low curvature. Received: 12 May 1997 Accepted: 20 October 1997