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Copolymers of N-vinylcarbazole (M1) and N,N-dimethylaminoethyl acrylate (M2) were prepared by free radical polymerization in toluene or DMF solution at 60°C, using 2,2 0 -azobisisobutyronitrile (AIBN) as initiator. The reactivity ratios of both the monomers were determined by the extended Kelen–Tüdös method and found to be r1 ˆ 0.52 ^ 0.05, r2 ˆ 0.56 ^ 0.05 (in toluene) and r1 ˆ 0.44 ^ 0.04, r2 ˆ 0.18 ^ 0.03 (in DMF). Copolymers prepared in toluene were also characterized by UV and 1H-NMR sepctroscopy, viscosity and number- average molecular weight measurements and glass transition temperature determinations. The solvent effect on copolymer composition and microstructure is discussed.

Детальніше...  

Reversed phase high performance liquid chromatography (HPLC) was employed to elucidate the composition distribution of partially hydrolysed samples of poly(vinyl alcohol) (PVOH), demonstrating that elution across a chromatogram proceeded from higher to lower degree of hydrolysis (DoH). Fractions isolated by preparative HPLC fractionation and characterised by 1H nuclear magnetic resonance spectroscopy (NMR) were used as HPLC standards to construct a calibration curve of retention time versus DoH, allowing for DoH determination of any PVOH sample once its chromatogram was available. Plots of cumulative and differential distributions as a function of DoH were determined, allowing for comparisons of samples having average DoH in the range 70–90 mol%. A second set of fractions originating from a parent polymer having different molar mass was also isolated to confirm that calibration was not influenced by molar mass or size exclusion effects.

Детальніше...  

The effects of copolymerization of poly(2-hydroxyethyl methacrylate) with oligo-(ethylene glycol) dimethacrylates (OEDs) on the ionic conductivity of the gel electrolyte copolymers was investigated. A series of HEMA-OED cross-linked copolymers were produced with the number of ethylene glycol units varying between zero (uncross-linked) and nine. The conductivity of samples containing distilled and deionized water (DDIW) and 1 M KBr electrolytes was characterized by AC impedance measurements. The relationship between the amount of water/salt solution contained within the gel electrolytes and resultant conductivity is investigated and discussed with reference to the free volume in the system. The free-volume characteristics were probed by positron annihilation lifetime spectroscopy (PALS), and the influence of free volume and the amount of water/solution in the gels on conductivity discussed. The results indicate a positive correlation between the amount of mobile conducting phase and the available free volume in the system, with the amount of conducting phase present matched by a proportionate amount of free volume in the gel. The system showed evidence of orthopositronium (oPs) inhibition in the ion containing samples when compared with the DDIW samples. Slight differences in the oPs pickoff rate recorded in DDIW and IBr solution are attributed to microviscosity differences between the two fluids, rather than oPs quenching

Детальніше...  

The zone-drawing (ZD) method was applied to poly(p-phenylene vinylene) (PPV) precursor films under various applied tensions and heater temperatures. The ZD precursor films were successively converted to PPV by heat treatment, and the structure and mechanical properties of the resulting ZD-PPV films were investigated. It was found that the draw ratio, orientation function, crystallinity and apparent crystallite size of the ZD-PPV films were 8.0, 0.74, 65.2% and 47.5 Å, respectively. The mechanical properties were improved by the ZD, and the dynamic storage modulus of the ZD-PPV film reached 33.7 GPa at room temperature and held at 11.5 GPa even at 300°C.

Детальніше...  

Eight new homo- and copolymers have been obtained by polycondensation of terephthalic acid and propyloxyterephthalic acid with two different second order NLO-active chromophores derived from 4-[N,N-bis(2-hydroxyethyl)amino]-benzaldehyde. Polymers exhibit good optical clarity, satisfactory thermal stability above the glass transition temperature and most of them are soluble in common organic solvents. Second order nonlinear optical properties of two corona poled polymer films were evaluated by second harmonic generation (SHG) measurements with an incident radiation of 1542 nm.

Детальніше...  

Kevlarw fiber surface structure was primarily and directly observed in the filament configuration by the tapping mode atomic force microscopy (AFM). The microfibrils feature was observed with an average width of 500 nm, composed of various types of periodical units of an average size 50 nm in a pleating appearance. At the less crystalline spot on the Kevlarw fiber surface, the periodical organizations exhibit the skin-core-like differentiation. In contrast, at the highly crystalline spot, the periodicity is more uniformly arranged by a rectangular network manner. Inverse gas chromatography (IGC) was used as a tool to investigate the surface structure heterogeneity by calculating the surface energy of different types of probes adsorbed on the Kevlarw fiber surface. The energy sites distribution plot of n-hexylamine adsorption at finite dilution exhibits a two-adsorbing-peaks curve. At the higher energy site, a possible hydrogen-bonding interaction was proposed between n-hexylamine and oxygen-containing groups formed at the less crystalline surface. According to the AFM and IGC results, a Kevlarw fiber surface organizations model at the nanometer scale was proposed.

Детальніше...  

The crystalline textures of a blend of linear polyethylene with low density polyethylene and a blend of deuterated linear polyethylene with low density polyethylene have been investigated as a function of rate of cooling from the melt. Differential scanning calorimetry, transmission electron microscopy and Fourier transform infrared spectroscopy have been used to study co-crystallization and phase segregation. On the basis of previous studies, the blend compositions were chosen so that the melt contained a single phase. Segregation between components was found to occur, as a result of crystallization, during cooling at all rates other than rapid quenching. The degree of segregation was found to increase with decreasing cooling rate. The morphologies resulting from this phase segregation during crystallization, have been compared with morphologies, previously determined, of blends of other compositions rapidly quenched from what was believed to be a phase separated melt. The scale of phase segregation is found to differ by more than an order of magnitude between the two types of morphology. The results support the argument that those rapidly quenched samples, which contain two crystal types, do so because of phase separation in the melt and not because of phase separation on crystallization. A comparison is made between two methods of sample preparation for transmission electron microscopy: permanganic etching/replication and chlorosulfonic fixation/sectioning. We have found the latter method better for revealing detailed morphological features between large lamellae

Детальніше...  

Change in the stress relaxation behavior of linear low-density polyethylene (LLDPE) with drawing and irradiation has been investigated. Samples of isotropic LLDPE were oriented to draw ratios l ¼ 6,9,11 and irradiated to integral doses between 35 and 500 kGy. Stress relaxation was interpreted in terms of a two-process model, first associated with the crystal and second with the amorphous fraction. Analyses of viscoelastic properties of these two fractions have revealed their different behavior upon drawing and irradiation.

Детальніше...  

The optical, morphological, thermal and redox properties of galvanostatically deposited poly(N-ethyl aniline) films are investigated. Effects of monomer concentration and substrate resistance on film properties have been reported. At higher concentration (0.8 and 1.0 M), the formation of a conducting phase with an absorbance maxima at ⬃ 840 nm is found to be more predominant. The substrate resistance also has a profound influence on the film properties in terms of rate and selectivity in deposition of the conducting phase. These results are supported by IR spectroscopy. The redox properties are affected by concentration of monomer while the substrate resistance contributes towards loss in reversibility of the species formed, especially at higher monomer concentration. Also, the morphology of the films exhibits improvement in quality with monomer concentration. The density of the fibres is affected by the decrease in substrate resistance. Thermal pattern also exhibits variation in terms of the number of steps involved in decomposition as well as the final decomposition temperature.

Детальніше...  

A computational strategy based on force-field calculations was developed to predict and analyze the packing in crystalline polymers. The strategy, which was incorporated in a computer program called Prediction of the Crystal Structure of Polymers (PCSP), takes advantage of the information provided by X-ray and/or electron diffraction. The program evaluates all the modes of packing for a given lattice dimensions, being able to predict the lowest energy one. The ability of the method to provide reliable results was proved by analyzing the crystal structure of four different polymers. Further, an insight on the applicability of the PCSP program to estimate the mechanical properties of polymers was provided by computing the elastic constants of the orthorhombic polyethylene.

Детальніше...  

Корисні статті

Полімерні матеріали

Полімер це велика молекула, або макромолекула, котра складається з багатьох субодиниць. Через їх широкий спектр властивостей, синтетичні і природні полімери відіграють найважливішу і всюдисущу роль в повсякденному житті. Полімери в діапазоні від знайомих синтетичних пластмас, таких як полістирол природний біополімер, таких як ДНК і білки, які є основоположними для біологічної структури і функцій. Полімери, як природні і синтетичні, створюються за допомогою полімеризації багатьох малих молекул, відомих як мономери.

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.

Інженер-механік

Інженер-механік (від лат. Ingenium – талант, обдарованість, і mēchanicus – механік) – це технічний чи технологічний фахівець з вищою освітою, який застосовує отримані знання для конструювання, проектування, моделювання та експлуатації машин, апаратів та технічного обладнання в різних галузях сільського господарства та технічного виробництва. Першими з інженерів були саме механіки; вони розробляли і збирали різноманітні машини і механізми, в яких використовували принципи і закони механіки.

Види та функції сучасної упаковки

Різноманітна упаковка щільно увішла у життя кожної людини. На полицях магазинів, в інтер'єрах помешкань можна побачити десятки пляшочок, коробок, аерозольних болончиків. Термін існування упаковки в нашому житті може продовжуватися від кількох хвилин до кількох років. Що ж таке сучасна упаковка? Чому вона займає стільки місця в нашому житті?

ВНЗ України

Вища освіта є невід'ємним елементом перспективного кар'єрного росту, тому перед кожним абітурієнтом виникає проблема, в які інститути подавати документи. Варто відзначити, що в Україні існує велика кількість вузів. Всі навчальні заклади поділяються на державні та приватні, пропонуючи різноманітні освітні програми по різних профілів. Щоб пошук інститутів дав задовільні результати, слід визначитися з найбільш прийнятними спеціальностями. Також підбір університету передбачає вибір підходящої форми навчання, наявність високої акредитації у вузу і рівень його престижності.