A Versatile Equilibrium Method for the Synthesis of High-Strength, Ladder-like Polyphenylsilsesquioxanes with Finely Tunable Molecular Parameters

A versatile equilibrium method for synthesizing ladder-like polyphenylsilsesquioxanes (L-PPSQs) with various molecular weights (from 4 to 500 kDa) in liquid ammonia was developed. The effect of diverse parameters, such as temperature, monomer concentration, reaction time, addition or removal of water from the reaction medium, on the polycondensation process was determined. The molecular weight characteristics and structure of the L-PPSQ elements obtained were determined by GPC, 1H, 29Si NMR, IR spectroscopy, viscometry, and PXRD methods. The physicochemical properties of L-PPSQs were determined by TGA and mechanical analyses.

Light-Induced Reactions within Poly(4-vinyl pyridine)/Pyridine Gels: The 1,6-Polyazaacetylene Oligomers Formation

Cyclic 6-membered aromatic compounds such as benzene and azabenzenes (pyridine, pyridazine, and pyrazine) are known to be light-sensitive, affording, in particular, the Dewar benzene type of intermediates. Pyridine is known to provide the only Dewar pyridine intermediate that undergoes reversible ring-opening. We found that irradiation of photosensitive gels prepared from poly(4-vinyl pyridine) and pyridine at 254 or 312 nm leads to pyridine ring-opening and subsequent formation of 5-amino-2,4-pentadienals. We show that this light-induced process is only partially reversible, and that the photogenerated aminoaldehyde and aminoaldehyde-pending groups undergo self-condensation to produce cross-linked, conjugated oligomers that absorb light in the visible spectrum up to the near-infrared range. Such a sequence of chemical reactions results in the formation of gel with two distinct morphologies: spheres and fiber-like matrices. To gain deeper insight into this process, we prepared poly(4-vinyl pyridine) with low molecular weight (about 2000 g/mol) and monitored the respective changes in absorption, fluorescence, 1H-NMR spectra, and electrical conductivity. The conductivity of the polymer gel upon irradiation changes from ionic to electronic, indicative of a conjugated molecular wire behavior. Quantum mechanical calculations confirmed the feasibility of the proposed polycondensation process. This new polyacetylene analog has potential in thermal energy-harvesting and sensor applications.

Synthesis of Monolithic TiO2 Aerogels With Relatively Low Shrinkage and Improved Formability Assisted by CTAB

Monolithic TiO2 aerogels without severe shrink were obtained by the sol-gel method with the addition of the surfactant cetyltrimethylammonium bromide (CTAB) to control the hydrolysis and polycondensation process and acetonitrile solvent as the solvent to improve the crystallinity. After CO2 supercritical drying, the shrinkage ratio of monolithic TiO2 aerogels modified by CTAB decreased by up to ∼26.9%, compared with the pure TiO2 aerogel. Their apparent densities were all lower than 300 g/cm3. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR) and BET Specific Surface Area Analysis were used to analyze the as-synthesized samples. The results revealed that all the samples were anatase-TiO2 phase with nanoporous network structures. The specific surface areas reached 250.2 m2/g confirmed by the BET (Brunaur–Emmett–Teller method) analysis. However, TiO2 aerogels without the addition of CTAB showed evident agglomeration and collapse of the network in comparison with CTAB-added samples. To further study the structure-property relationship, the photocatalysis performance of as-synthesized and 300°C-calcined aerogels was carried out contrastively. Interestingly, the influences of the CTAB adding amount of as-synthesized and calcined TiO2 aerogels are negative and positive, respectively, which is probably due to the synergistic effect of CTAB hindrance and grain refinement. Potentially, This kind of TiO2 aerogels assisted by CATB with low density, small shrinkage, improved formability, high specific surface area and fine crystalline grain may be applied in various applications, such as electrochemistry, photocatalysis, etc.

Thermal Polycondensation Process and Oil Furnace Production

The article discusses the methods of obtaining petroleum pitch of thermal polycondensation. The main attention is paid to the characteristics of petroleum pitch, its properties, its comparison with coal-tar pitch, the advantages of petroleum pitch in comparison to coal-tar pitch, the processes of production of petroleum pitch by thermal polycondensation are given. Three promising technologies for the production of petroleum pitch have been identified: thermal polycondensation of cracking residue, high-temperature thermal polycondensation of petroleum feedstock and thermal polycondensation of pyrolysis resin according to a two-stage scheme. Methods of obtaining petroleum pitch in laboratory conditions, such as thermal polycondensation under pressure and heat treatment under reduced pressure, are presented. The urgency and feasibility of developments for the creation of petroleum pitch and the introduction of thermopoly-condensation processes in Russia is emphasized.

STUDY OF POLYCONDENSATION PROCESS OF CARBAMIDE WITH FORMALDEHYDE TO RECEIVE BIODEGRADABLE POLYMERS

Biodegradation of polymers of spatial structure is complicated at the impact of soil destructive microorganisms and biodegradation requires long time. We have implemented target-oriented synthesis of a polymer to receive linear structure polymers where labile peptide bonds are preserved.To implement target-oriented synthesis of a polymer and to determine optimal conditions for reaction mechanism we studied the process of kinetics and its regularities – reaction temperature, duration, components ratio, concentration, reaction speed constant and activation energy. The Arrhenius factor and succession of introduction of initial components to the reaction medium were computed, catalyst nature and other properties were determined.High effect of prolongation was achieved, when carbamide and formaldehyde molar ratio was 1:1. In this case linear structure polymer is formed where peptide -CH2 – NH – are preserved.The simplified structure of linear polymer is expressed as followed: – HNCONHCH2[ NHCONHCH2 ]n – HNCONHCH2 – .

Synthesis and Structural Characterization of Sequential Structure and Crystallization Properties for Hydrophilic Modified Polyester

The hydrophilic copolyester polyethylene terephthalate (PET) (ENCDP-X) was successfully synthesized by chemical modification consisting of copolymerization and blending and the comonomers, including sodium isophthalate-5-sulfonate (SIPE), polyethylene glycol (PEG), 2,2-dimethyl-1,3-propanediol (NPG) and matting agent TiO2 with different content. Moreover, the structural characterization of sequential structure, crystallization and thermal properties were studied. The results showed that the comonomers were successfully embedded in the copolyester, the actual molar ratio in the copolyester was consistent with the relative feed ratio and the degree of randomness was calculated to be 0.99, showing that the random copolymers synthesized during the melt polycondensation process and the chemical structure was roughly consistent with the expected molecular chain sequence structure. The thermal parameters of the modified copolyester, containing the glass transition temperature (Tg), melting point (Tm), crystallinity (Xc) and thermal degradation temperature, were decreased, and the cold crystallization temperature (Tc) was increased. In addition, with the increasing of the TiO2 content, it improves the thermal performance of the copolyester and it is beneficial to processing and application. The above conclusion is further verified by non-isothermal kinetic analysis. In addition, the copolyester exhibited the better hydrophilicity than pure PET.

Polyurethane and Polyurethane Nanocomposites: Recent Contributions to Medicine

Polyurethane (PU) is a synthetic polymer obtained by polycondensation process of isocyanates and polyols, and for some cross-linked products with a third component as an extender. It is one of the most versatile macromolecular compounds, and it contains soft and hard segments. Beside (PU)'s physicomechanical and chemical properties, which make them suitable to be used in many engineering areas, they are biocompatible, biodegradable, bioabsorbant, and bioinert, characteristics which recommend them to be used in different medical areas. For instance, PUs and, more recently, their nanocomposites are used for wound dressing, antibacterials, tissue engineering, scaffolds, drug delivery, and even medical devices.