-
Головна
-
Журнал Polymer
- 1994 рік
1994 рік
Exposure of amorphous poly(ether ether ketone) (PEEK) to the organic solvent 1,1,2,2-tetrachloroethane (TCE) was found to have considerable effects on the physical and spectral properties of PEEK. TCE causes significant bulk swelling, as well as inducing polymer chain crystallization. Lewis acid-base interactions between the polymer and the solvent are the likely explanation for this enhanced solvent compatibility
Self-diffusion, viscosity and spin-spin relaxation have been measured for a series of low molecular weight liquid poly(propylene oxide) melts. The data are discussed within the framework of theories commonly invoked for polymer dynamics including the Rouse chain and free volume effects. The average diffusion coefficients of a range of bimodal blends have also been measured and the results interpreted using the Rouse model.
The crystallization behaviour of an e-caprolactone-block-butadiene diblock copolymer was observed by small-angle X-ray scattering employing synchrotron radiation. The processes of primary and secondary crystallizations were separately analysed by procedures usually used for homopolymer crystallization, and were compared with the case of a poly(e-caprolactone) homopolymer (PCL). The Avrami analysis at the primary crystallization showed an exponent n ranging from 2 to 3. This value is comparable to n evaluated for PCL and also n widely reported for crystalline homopolymers, indicating that the crystallization of the PCL block drives the primary stage without the influence of the existing microphase structure of the block copolymer. In the secondary crystallization, on the other hand, the rate was significantly retarded when a microphase structure existed in the system.
Poly(methylphenylsilane) has been synthesized through homogeneous reductive dechlorination of dichloromethylphenylsilane using sodium/electron-acceptor complexes in tetrahydrofuran solution at -79°C. The optimization of product molecular weights is considered through analogy to a step-growth polymerization
The effects of draw conditions on the deformability and efficiency of uniaxial draw were studied for solution-spun fibres from high molecular weight poly(ethylene terephthalate) (intrinsic viscosity = 2.6 dl g- t). The fibres could be drawn up to a draw ratio of 16.4 by three stages of draw (tensile draw at 80°C + solid-state coextrusion at 90°C + tensile draw at 200°C). During the solid-state coextrusion, crystal destruction and orientation of non-crystalline segments in the predrawn fibres took place, leading to further deformation at the third stage of draw. The tensile modulus and strength of the resultant highly drawn fibres reached 39 and 2.3 GPa, respectively. The improved ductility and efficiency of draw developed as a result of changes in supermolecular structure and in the number of net points due to entanglements and stress-induced crystals during deformation
By means of the pulsed-field gradient nuclear magnetic resonance method, the tracer diffusion of homopolymer chains dissolved in the microphase domain of block copolymer mesophase has been studied for two systems: poly(dimethylsiloxane) (PDMS) in polystyrene(PS)-b-PDMS in the presence of d6-benzene as a plasticizer, and poly(ethylene glycol) (PEG) in PS-b-poly(hydroxystyrene-g-PEG)-b-PS. Comparing the diffusion coefficient D of the tracers in the block copolymer matrices with the self-diffusion coefficient D s of the pure tracers, two regimes with a different dependence of D/D s on the molecular weight M of the tracers have commonly been found in the two systems. In the lower M regime (regime I), the ratio D/D s increased remarkably with increasing M, whereas in the higher M regime (regime II), the value of DID s was ~0.15 and was independent of M. This behaviour could be explained by the M dependence of the spatial distribution of the tracer chains in the microphase domain. In regime I, the tracers deeply penetrate into the brushes of the PDMS or grafted PEG with the depth decreasing with increasing M, while in regime II the tracer chains do not penetrate well into the PDMS or PEG brushes, but rather are interposed between the layers.
The diffusional behaviour of sodium salicylate (SSA) from a new chemically crosslinked copolymeric hydrogel of 2-hydroxyethyl methacrylate with N,N'-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)ammonium betaine is reported. The drug release into water was effected under sink conditions and the kinetics at 310 K were followed by continuous measurement of conductivity. A modified form of Fick's second law has been derived to take into account the dimensional changes of copolymer during drug release, which were measured photographically. The procedure was used to evaluate the diffusion coefficient D s for transport of SSA into water. The value of D s = 4.4 x 10-11 m 2 s- 1 yielded over a range of drug loading is smaller than the load-dependent values obtained when allowance is not made for dimensional changes. The procedure has also been used to determine the diffusion coefficient for water into polymer
A series of phenylated, aromatic poly(pyridinium tetrafluoroborate)s has been prepared by the polymerization of 4,4'-(1,4-phenylene)bis(2,6-diphenylpyrylium tetrafluoroborate) with aromatic diamines in a dimethylsulfoxide/toluene mixture at 145-150°C. The water generated by the transformation of the pyrylium rings to pyridinium rings was distilled from the reaction mixture as a water/toluene azeotrope. All-para-catenated, rigid-rod polymers with inherent viscosities as high as 4.9 dl g 1 were obtained that were soluble in polar aprotic solvents. The polymers could be solution cast into tough, flexible films. Although the glass transition temperatures of the poly(pyridinium salt)s were difficult to detect with differential scanning calorimetry, they displayed distinctive melting endotherms with minima above 380°C. Thermogravimetric analysis showed that the polymers began to decompose near 360°C prior to melting. Wide-angle X-ray diffraction analysis revealed that the chains were packed in a structure similar to that of a smectic liquid crystalline glass.
Welding experiments using a double cantilever beam test geometry for a miscible poly(styrene-coacrylonitrile)/ poly(methyl methacrylate) (SAN/PMMA) system showed the expected linear increase of the fracture toughness, Ga, with the root of annealing time. For immiscible pairs of PMMA and SAN it was found that G a increases linearly with the equilibrium interfacial thickness or, equivalently, to Z- 1/2, Z being the Flory interaction parameter
The dielectric relaxations of poly(dimethylphenyl methacrylate)s were studied over a wide frequency and temperature range by two methods. The ct relaxation, associated with the glass transition temperature, was studied by classical dielectric measurements. Thermal peak cleaning was used to deconvolute the global thermally stimulated current spectra over the range of low temperatures, corresponding to the fl relaxation. The ~ relaxation involves long-range, generalized and highly cooperative motions of the main chain. They are influenced by the steric hindrance and dipole~lipole interactions relative to the position of the CH 3 group of the aryl ring in the polymer repeat unit. As a first approximation it was assumed that the fl process was related only to local motions of the side group, but the activation parameters are too high to be consistent with this assumption. Therefore it was concluded that intermolecular factors and local motions of the main chain could also be involved
Корисні статті
Хімічне машинобудування
Хімічне машинобудування багатопрофільна галузь машинобудування, що поєднує в собі природні та експериментальні науки (наприклад, фізика і хімія), разом з науками про життя (наприклад, біологія, мікробіологія та біохімія). Математику та економіку вокористовують для розробки, перетворення, транспортування, управління виробничими процесами, які перетворюють сировину в цінні продукти.
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?
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).
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.
Комп'ютер для інженера
У сучасному світі комп'ютери дуже поширені. Складно уявити людину, не знайому з цим поняттям. Багато професій зобов'язані своїм виникненням саме комп'ютеру, вони б просто не з'явилися без створення електронно-обчислювальної техніки.
І хоча відносно недавно, на початку XX століття, комп'ютери були розкішшю і використовувалися лише для самих складних розрахунків, у наш час комп'ютери та комп'ютерна техніка дуже глибоко інтегрувалися у наше життя. Сучасне людство залежить від комп'ютерів, що викликає подиву, якщо розглянути, коли і в яких випадках вони використовуються.
