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The oxidative polymerization of aniline by (NH4)2520 s in dilute solutions of HC104 or HCI of various concentrations was investigated. The reactions were terminated at various times and the solid products were isolated and analysed using Fourier transform infra-red and ultraviolet-visible absorption spectroscopy and X-ray photoelectron spectroscopy. The ultraviolet-visible absorption spectra of the reaction mixtures and the structure of the initial solid products indicate different initial reaction pathways and intermediates occurring under the conditions tested. At low acid concentrations, the solids that are initially precipitated out are salts of short-chain oligomers with the anions from the protonic acid as well as sulfate anions. In contrast, at low pH, the long-chain, para-disubstituted nature of the solid is evident at the initial stages and the counterions are predominantly supplied by the protonic acid. With decreasing acid concentration, although the polymerization rate decreases, a long-chain para-disubstituted polymer is ultimately obtained, albeit with an increase in the proportion of sulfate anions serving as counterions and in the amount of unprotonated imine units. A comparison of the thermal stability of the various polymers indicates a significantly lower decomposition temperature for the polymers obtained at low acid concentrations or short reaction time.

Детальніше...  

The state of sorbed water in nylon-6 membranes grafted with acrylic acid (AA), acrylamide (AM) and p-styrenesulphonic acid (SS) was investigated by differential scanning calorimetry. There are three kinds of water in AA- and AM-grafted nylon-6 membranes: non-freezing water, intermediate water and free water. The SS-grafted nylon-6 membrane retains both non-freezing water and freezing water. In the latter, the intermediate water and the free water cannot be distinguished. Each kind of grafted membrane with high extent of grafting can retain a good deal of the non-freezing water and the intermediate water. This is due to an increase in the content of hydrophilic repeat units as graft copolymerization progresses. The SS repeat unit can retain a larger amount of water than can AA or AM. It was also found that the amount of non-freezing water per repeat unit increased in the order of AA-, AM- and SS-grafted nylon-6 membranes. The order reflects the nature of the homopolymers

Детальніше...  

Monodisperse linear polytetrahydrofuran (PTHF) chains with unreactive end groups were mixed with PTHF chains with reactive ends. The concentration of the linear unreactive chains was dilute, approximately 3 wt%. The phase behaviour as well as the single chain conformation of the unreactive chains was investigated after the reactive chains were end-linked via either a tetrafunctional crosslinker or a free radical polyaddition reaction. The results were found to depend strongly on the difference in the molecular weights between the reactive chains and the unattached linear chains.

Детальніше...  

A well-defined poly[styrene (S)-b-2-vinylpyridine (2VP)] diblock copolymer was prepared by sequential anionic addition. The polystyrene (PS) block part of this diblock copolymer contained a small amount of isoprene (I) sequence units at the prescribed position. The crosslinking reaction of the block copolymer film with poly(2-vinylpyridine) (P2VP) spherical microdomains was carried out with 1,4-diiodobutane (DIB) vapour. Electron micrographs and particle size distribution of this crosslinking product showed the microstructure of core-shell type polymer microspheres. Cores and shells were formed by crosslinked P2VP blocks and PS branchings, respectively. Subsequently, ozonolysis of isoprene sequences on the core-shell type microspheres was performed in a chloroform solution. Through ozonolysis, the arm chains composed of PS blocks were cleaved at the 1,4-linkage of isoprene units. It was indicated from the dynamic light scattering that the shell thickness on the core-shell type microsphere decreased after ozonolysis. The arm length of PS branching was able to be controlled by ozonolysis at the position of the introduced isoprene units.

Детальніше...  

Several toluene diisocyanates blocked with various substituted phenols were prepared. They were characterized by elemental analysis, infra-red and 1H nuclear magnetic resonance spectroscopy. The deblocking temperatures were determined by use of infra-red spectroscopy and by carbon dioxide evolution methods. The thermal stability of the blocked isocyanate was less for the ortho-substituted phenols than for the para isomers. Dissociation temperatures were also reduced by electron-withdrawing groups. The dissolution temperatures of the adducts were determined in propylene glycol, poly(ethylene glycol) 400 and hydroxyl-terminated poly(butadiene).

Детальніше...  

Several investigations show that the unperturbed dimensions of a given polymer in any solvent do not depend on the nature of the solvent, as far as the solvent has no influence on the rotation of the chain segments. In this case K o is a constant. The evaluation of K e from [t/]-M data by application of the classical Burchard-Stockmayer-Fixman (BSF) theory often results in different values, with dependence on solvent power and, with mixed solvents, on solvent composition. This is mainly due to the non-linearity of the relationship, especially with high molar mass polymers in good solvents. Better results are obtained by non-linear graphical treatment of the BSF plot, or by application of a modified equation proposed by Tanaka, which takes into account the general ~5 z relationship between molecular expansion factors and the excluded volume parameter z. Plots of ([q]/M°'5) 5/3 versus M °5 show linearity over nearly the entire range of molar mass studied and evaluation of unperturbed dimensions results in a quasi unique value of K o for a given polymer.

Детальніше...  

The quaternary salt of N,N'-dimethylaminoethyl methacrylate with dimethyl sulfate has been synthesized and its polymerization has been studied in aqueous solutions, using K2S208 as initiator, as well as in dimethylformamide, dimethyl sulfoxide and ethanol in the presence of azobisisobutyronitrile. Exponents expressing the dependency of initial polymerization rate on monomer and initiator concentrations at 60°C were 1.6 and 0.5, respectively and the overall activation energy in the temperature range 40-60°C was 92.8 kJ tool-1 (for aqueous systems). Polymeric quaternary salts (PQS) synthesized in various solvents differ in their intrinsic viscosity and the initial rate of polymerization is found to decrease with decreasing dielectrical constant of the solvent. By means of viscometry, conductometry and electrochemical analysis, PQS have been characterized as strong polyelectrolytes.

Детальніше...  

The gel of radiation crosslinked poly(ethylene oxide) (PEO) was used as a highly active phase transfer catalyst in the model displacement reaction of 1-bromooctane with aqueous sodium and potassium cyanides in the absence of organic solvent. The reaction follows pseudo-first-order kinetics and the rate is linearly dependent on the amount of PEO gel. The reaction rate is not limited by intraparticle diffusion and mass transfer at stirring speeds above 200 rev min-1. Crosslinked PEO is easily produced in large quantities from commercially available polymer so it may be used successfully as a gel medium for phase transfer catalysis in various substitution reactions.

Детальніше...  

Swelling experiments were carried out with three cationic polyelectrolyte gels of N-n-butyl-4-vinylpyridinium bromide (BPyBr), N-n-butyl-N,N-dimethyl-4-vinylanilinium bromide (BAnBr) and N-n-butyl-N,Ndimethyl-( N'-acryloyl-3-aminopropyl)ammonium bromide (BAPABr). The swelling equilibria of the gels were measured in aqueous solutions of inorganic electrolytes: HBr, NaBr, KBr, NaCI and NaI. The swelling ratios of the gels did not depend on the cationic species of the electrolytes examined but depended strongly on the anionic species. Volume phase transitions were not observed with the BPyBr and BAnBr gels in aqueous solutions of NaC1 and NaBr whereas a phase transition was observed in an aqueous solution of NaI. The NaI concentration at which the phase transition occurred was raised with an increase in temperature. On the other hand, no discontinuous change was observed in the swelling equilibria of the BAPABr gel, even in the NaI aqueous solution. Comparison of the present results for the BAPABr gel with previous results for a polyelectrolyte gel verified the importance of hydrophobic interactions, which enhance the occurrence of volume phase transitions.

Детальніше...  

The effect of the introduction of metal on the physical and electronic properties of a functional polymer, poly[4-(terephthaloylamino)salicylic acid hydrazide], PTASH, has been investigated. Cu(II), Ag(I), Ni(II) and Co(II) chelates of the polymer were prepared. The results revealed that metal ions were chelated with the PTASH repeating unit in a ratio of 1:1. The structure of the resulting chelates was determined by elemental analysis and i.r. spectroscopy. The chelates showed good solubility in several common organic solvents. Thermal gravimetric analysis showed that the chelates are characterized by high thermal and thermo-oxidative stabilities and the degradation temperatures ranged from 510 to 585°C in air and from 555 to 610°C in a nitrogen atmosphere. The chelates were found to become electronic conductors upon treatment with various reducing agents. Their electrical surface resistivities ranged from 5.3 x 105 to 0.5 x 10- 2 f~ mm- 2 and were affected by the amount of metal incorporated onto the polymer chains. The electrical conductivities of the reduced chelate films are attributed to the formation of a metallic surface layer by the action of reducing agents. This layer is illustrated not only by the lustrous metallic appearance of the chelate film surfaces but is also confirmed by X-ray diffraction and SEM. Further, all the metal chelates studied here are flexible and possess higher tensile strength than the non-chelated PTASH.

Детальніше...  

Корисні статті

Інженер-машинобудівник

Ні для кого не секрет, що при сучасних умовах життя, темпах розвитку промисловості, безперервній автоматизації та оптимізації роботи механізмів та виробничих процесів, великою популярністю та попитом на ринку праці користується професія інженера, особливо інженера-машинобудівника.

Щоб відповісти на питання «Хто такий інженер-машинобудівник?», необхідно розуміти , що несе в собі кожне з цих слів окремо. Інженер – це людина, яка отримала освіту з визначеного фаху. Інженер – це творець техніки. Інженер – це особа, що професійно займається інженерією, тобто на основі поєднання прикладних наукових знань, математики та винахідництва знаходить нові рішення технічних проблем. Тобто, виходячи з цих загальновживаних визначень слова «інженер» зрозуміло, що цій професії може присвятити себе лише людина з неабиякими здібностями, які ґрунтуються на знанні точних наук, логічному мисленні, невичерпному терпінні і постійному бажанні вдосконалювати світ інженерії. Від латини ingenium — здатність, винахідливість, що є свідченням того, що інженером перш за все є людина-думаюча, яка знаходиться в безперервному пошуку відповідей на складні технічні завдання.

Що таке КПІ?

На сьогоднішній день багатьох випускників, ще недавно – школярів, цікавить наступне питання – куди поступити, куди піти навчатися? В нашій країні є дуже багато ВНЗ, які пропонують свої послуги з підготовки і навчання студентів. Одним з таких ВНЗ є Київський політехнічний інститут (КПІ).

Вибір професії

Кожна людина зіштовхується у своєму житті з вибором, який найсильніше вплине на все її подальше життя. Йдеться про вибір професії та вибір вищої освіти. Закінчуючи школу, молоді люди стикаються з величезним вибором професій та спеціальностей: інженер, економіст, юрист, менеджер, маркетолог, логіст, фінансист і т.д. При цьому навколо можна чути безліч стереотипних фраз: "Юристи багато заробляють", "Фінансисти працюють з грошима, тому у них хороші зарплати", "Маркетолог - основний людина в будь-якому бізнесі", а часом і просто без обґрунтування - "Менеджер - це круто ". Часом, такі "поради" впливають на вибір професії.

Рейтинг вищих навчальних закладів

На даний час в світі існує маса університетів з дуже великою кількістю кваліфікацій, спеціальностей та спеціалізацій. Одні з них більш престижні університети, інші менш.

Рейтинг вищих навчальних закладів переписується щорічно, в зв'язку з тим, що всі прагнуть стати краще в освіті, вдосконалитися в технологіях і підвищити свій рівень акредитації. Рейтинг навчальних закладів варіюється в залежності від предметної області, це природничі науки і математика, техніка/технологія і інформатика, життя і сільськогосподарська наука, клінічна медицина і фармація, соціальні науки.

Як стати інженером?

Кожна людина в процесі свідомого життя стикається з проблемою вибору професії. Найбільш актуальною ця проблема є для учнів старших класів – випускників, які добровільно або примусово здають шкільні іспити та зовнішнє незалежне оцінювання, за результатами чого приймають участь в конкурсному відборі на навчання у ВНЗ. Щоб обрана професія не стала важким випробовуванням, потрібно ще у шкільні роки зважити всі «за» і «проти», оцінити свої здібності, схильності, можливості.