Catalytic Polymerization of Phthalonitrile Resins by Carborane with Enhanced Thermal Oxidation Resistance: Experimental and Molecular Simulation

Biphenyl phthalonitrile (BPh) resins with good thermal and thermo-oxidative stability demonstrate great application potential in aerospace and national defense industries. However, BPh monomer has a high melting point, poor solubility, slow curing speed and high curing temperature. It is difficult to control the polymerization process to obtain the resins with high performance. Here, a BPh prepolymer (BPh-Q) was prepared by reacting 1,7-bis(hydroxymethyl)-m-carborane (QCB) with BPh monomers. The BPh-Q exhibited much better solubility, faster curing speed and lower curing temperature compared with pure BPh and BPh modified with bisphenol A (BPh-B, a common prepolymer of BPh). Thus, the polymerization process of BPh was greatly accelerated at a low temperature, resulting in a BPh resin with enhanced thermostability and oxidation resistance. The experimental and theoretical models revealed the promotion effect of B-H bond on the curing reaction of phthalonitrile via Markovnikov addition reaction due to the special steric structure of carborane. This study provided an efficient method to obtain low-temperature curing phthalonitrile resins with high thermal and thermo-oxidative resistance, which would be potentially useful for the preparation of high-performance cyanide resin-based composites.

Obtaining and Research of Palladium Complexes with 4-aminopiridine

The obtaining and investigation of various complex compounds of the biologically active aromatic heterocyclic ligands with platinum and palladium are of interest due to their potential medical applications. To that end, 4-amino pyridine containing cyclic and exocyclic nitrogen atoms has been used. The main aim of this work is to clarify which nitrogen atom of the ligand composes stronger and more stable bond. For that purpose, the synthesis of palladium salts with ligand has been accomplished within a wide interval of pH (3-12) and temperature (50-800C). The cation-anion and neutral complex compounds have been obtained depending on stoichiometric ratio of the reacting components, temperature and pH and was further studied. As a result of IR-spectroscopic investigation of synthesized complexes, the acquired information demonstrated that the pyridine nitrogen atom of the ligand is protonated and composes outer sphere as monocharged cation. However, tetraacidoanion is formed in the inner sphere. In the alkaline medium the ligand is monodentately coordinated with palladium through nitrogen atom of pyridine. The exocyclic nitrogen atom of the ligand does not participate in the coordination regardless of pH of the medium and stoichiometric ratio of the taken compounds. As a result of investigation of the thermal stability of the complexes it was determined that the neutral complexes are decomposed without melting at higher temperature than cation-anion complexes. It has been found that one of the factors that affects thermal stability is the steric structure of the complexes. The initial biological probes were accomplished and the correlation between their biological activities, composition and structures of complexes were determined. Despite the fact of taking the same medium and ligand, the cation-anion complexes indicate completely different biological activities than neutral ones.

Complexes of aluminum, iron(III), and gallium(III) chlorides with ethers in synthesis of highly reactive polyisobutylene

In this review, the latest achievements in the field of cationic polymerization of isobutylene catalyzed by the complexes of conventional Lewis acids with ethers are presented. The experimental and computational data on the influence of steric structure and basicity of ether used for the preparation of the Lewis acid-ether complex on the catalyst activity and regioselectivity of β-H abstraction are discussed here. Complexes of metal halides with linear (Bu2O) and moderately branched (iPr2O) ethers of moderate basicity (pKa from –4.3 to –5.4) displayed the highest activity and regioselectivity in the cationic polymerization of isobutylene affording highly reactive polyisobutylene (HR PIB) – the key intermediate in the preparation of motor oil and fuel additives. The review is also focusing on the adaptation of the developed catalytic system to the industry, which consists in using non-polar hydrocarbon solvents, high temperatures and monomer concentrations.

Periphery Decorated and Core Initiated Neutral and Polyanionic Borane Large Molecules: Forthcoming and Promising Properties for Medicinal Applications

A mini-review based on radial growing macromolecules and core initiated Borane periphery decorated with o-carboranes and metallacarboranes that has been developed in the authors laboratories is reported. The review is divided into four sections; three of them are related to the design and synthesis of these large boron-containing molecules and the fourth deals with the unique properties of anionic metallacarborane molecules that provide a glimpse of their potential for their promising use in medicinal applications. Their unique stability along with their geometrical and electronic properties, as well as the precise steric structure of 1,2-closo-C2B10H12 (o-carborane) that has the potential for the incorporation of many substituents: at the carbon (Cc), at the boron and at both carbon and boron vertices, suggests this cluster as an innovative building block or platform for novel applications that cannot be achieved with organic hydrocarbon compounds. Poly(aryl-ether) dendrimers grown from fluorescent cores, such as 1,3,5-triarylbenzene or meso-porphyrins, have been decorated with boron clusters to attain rich boron containing dendrimers. Octasilsesquioxane cubes have been used as a core for its radial growth to get boron-rich large molecules. The unique properties of cobaltabisdicarbollide cluster, which include: i) self-assembly in water to produce monolayer nano-vesicles, ii) crossing lipid bilayer membranes, iii) interacting with membrane cells, iv) facilitating its visualization within cells by Raman and fluorescence techniques and v) their use as molecular platform for “in vivo” imaging are discussed in detail.

Effects of End-Caps on the Atropisomerization, Polymerization, and the Thermal Properties of ortho-Imide Functional Benzoxazines

A new type of atropisomerism has recently been discovered in 1,3-benzoxazines, where the intramolecular repulsion between negatively charged oxygen atoms on the imide and the oxazine ring hinders the rotation about the C–N bond. The imide group offers a high degree of flexibility for functionalization, allowing a variety of functional groups to be attached, and producing different types of end-caps. In this work, the effects of end-caps on the atropisomerism, thermally activated polymerization of ortho-imide functional benzoxazines, and the associated properties of polybenzoxazines have been systematically investigated. Several end-caps, with different electronic characteristics and rigidities, were designed. 1H and 13C nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations were employed to obtain structural information, and differential scanning calorimetry (DSC) and in situ Fourier transform infrared (FT-IR) spectroscopy were also performed to study the thermally activated polymerization process of benzoxazine monomers. We demonstrated that the atropisomerization can be switched on/off by the manipulation of the steric structure of the end-caps, and polymerization behaviors can be well-controlled by the electronic properties of the end-caps. Moreover, a trade-off effect were found between the thermal properties and the rigidity of the end-caps in polybenzoxazines.