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Blends of rod-like PMDA-B (pyromeltitic dianhydride-benzidine) and semi-flexible 6FDA-PDA (6F-dianhydride-phenylenediamine) polyimides with several different compositions were prepared. According to the results from X-ray diffractometry and FTi.r. spectrometry, these two polyimides are incompatible when mixed at room temperature for 20 min. When mixed at 50°C for 40 h, the polymers, thermodynamically incompatible, become compatible owing to exchange reactions. Bending beam diffusion experiments show that the diffusion of moisture in these films belongs to case I. The diffusion constant D is 0.10 x 10-9 cm 2 s- ~ in PMDA-B and 1.65 x 10-9 cm 2 s- ~ in 6FDA-PDA. In the blends, D increases with increasing content of 6FDA-PDA. The slow diffusion in PMDA-B can be attributed to its highly crystalline structure and relatively small interchain spacing. The diffusion of moisture is faster in the compatible films. Regardless of compatibility, diffusion in all the blends is much slower than in pure 6FDA-PDA. This can be attributed to the comparatively small average interchain spacings of the blends.

Детальніше...  

The synthesis and free radical polymerization of N-(4-methacryloyloxyphenyl), 2-(4-methoxyphenyl) acetamide (OM), a methacrylic derivative of 4-methoxyphenylacetic acid (a non-steroidal antiinflammatory compound) is described. Also the introduction of a residue of 4-aminophenol (an analgesic and antipyretic metabolite) has been designed, in order to obtain macromolecules supporting two pharmacological residues with complementary action per repeat unit. The stereochemical configuration of POM chains has been analysed by ~H and 13C n.m.r, spectroscopies; polymers prepared by a free radical mechanism at temperatures of 50 and 70°C, are predominantly syndiotactic and follow a Bernoullian distribution of tactic sequences, with an isotacticity parameter tr = 0.27, very close to that of the free radical polymerization of 4-(methacryloyloxy)acetanilide (tr = 0.26 ), but slightly different to that of methyl methacrylate (a = 0.22). The results are interpreted in terms of the influence of the aromatic character of the side substituents on the pseudoasymmetric quaternary carbon of the methacrylic units.

Детальніше...  

The pyrolysis or decomposition products of cured, fire retardant epoxy resin (diglycidyl ether of tetrabrominated bisphenol A) were compared under several different conditions: thermal pyrolysis, laser ablation and cw laser pyrolysis. Volatile neutral products were ionized by electron impact, except in the case of direct laser ionization, and detected by Fourier transform mass spectrometry. Pyrolysis gave high molecular weight fragments and a considerable amount of information about the monomer composition. Detection of directly ionized, laser-ablated products gave some molecular fragments from microprobe sample sizes, although the spectra are complex. Laser ablation/electron impact ionization produced mostly low molecular weight fragments that gave limited information about the material. Laser pyrolysis using a cw argon ion laser provided some large fragments and consumed small amounts of sample. The relationships and analytical value of these techniques are discussed.

Детальніше...  

The secondary (7) relaxation modes of the polycarbonate of bisphenol A (PC) in the glassy state are discussed. Dynamic mechanical spectra of PC, its mixtures with plasticizers and oligomers, its blends with tetramethyl polycarbonate, as well as spectra of modified polycarbonates and of PC under stress are shown. The evidence suggests that the motions active in glassy PC are intramolecularly cooperative torsional 'local-mode' motions of backbone segments with about 5-7 monomer units. Cooperativity can be reduced or enhanced ; it is controlled by the tightness of the matrix. Intermolecularly the motions are not cooperative.

Детальніше...  

To understand the variation in blood contacting properties of chemically modified polyurethane, methyl methacrylate has been grafted on to polyurethane by the ),-irradiation method. The preliminary in vitro blood compatibility studies indicated an improvement in the blood contacting properties of polyurethane by the introduction of poly (methyl methacrylate) chains.

Детальніше...  

The effect of varying the homopolymer molecular weight, corresponding to the minor phase, on the interfacial activity of graft copolymers in blends of homopolymers has been investigated. The system studied was polycarbonate/poly(methyl methacrylate) (PMMA) (65/35w/w) blends containing polycarbonate/ PMMA graft copolymers. The molecular weight of the polycarbonate homopolymer was increased from 3.6 to 52.4kgmol-1, always maintained lower than that of the polycarbonate block (143.8 kgmol-1). Molecular weights of all other components were kept constant. Copolymer interfacial activity, in terms of its efficacy to reduce the size of the dispersed phase and create interface, deteriorated considerably with increasing polycarbonate homopolymer molecular weight. The interfacial area occupied by a single copolymer molecule did not change dramatically. This behaviour was observed with constant (10% w/w) and varying (1-40% w/w) copolymer content. In dilute solutions (1 x 10-3g cm-3) with selective solvents (toluene), the copolymer formed micelles consisting of approximately nine copolymer molecules with no evidence for significant swelling of the polycarbonate core by unreacted polycarbonate homopolymer. Thermodynamic parameters of aggregation showed the process to be enthalpy driven. Copolymer interfacial activity is discussed in terms of phase diagrams for these systems with increasing homopolymer molecular weight. Phase separation of copolymer and polycarbonate homopolymer from the PMMA-rich matrix as the system crosses the b/nodal has been argued to be the mechanism to account for the presence of stable fine polycarbonate-rich dispersions in a PMMA-rich matrix. The relative molecular weight of the polycarbonate homopolymer to that of the polycarbonate block controls the position of the critical copolymer-homopolymer concentration relative to that of the overall system

Детальніше...  

Poly(3,4'-oxydiphenylene pyromellitimide) (PMDA-3,4'-ODA), an isomer of poly(4,4'-oxydiphenylene pyromellitimide) (PMDA-4,4'-ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4'-oxydiphenylene diamine (3,4'-ODA). For these two polyimide isomers and their poly(amic acid) precursors in the condensed state on Si wafers, residual stress behaviour over the range 25-400°C was investigated by the dynamic measurement of wafer bending. During thermal imidization both isomers did not show any difference in stress versus temperature behaviour. Once imidized, however, one isomer exhibited a quite different stress behaviour from that of the other during cool-down: the stress of PMDA-3,4'-ODA increased rapidly from zero at 400°C to ~45 MPa at 40°C, whereas that of PMDA-4,4'-ODA rose gradually from zero to ~27 MPa. For both cured isomers, stress-temperature profile on heating was the same as that on cooling, with some deviation due to moisture uptake over the temperature range 25-150°C, indicating that their stresses were insensitive to thermal cycling or thermal annealing. From independently measured properties (thermal expansion coefficient, modulus, Poisson's ratio of 0.34) of both polyimides, the thermal stresses were calculated and compared with the measured overall stresses. It is concluded that for both polyimides the overall residual stress results primarily from the thermal stress. In comparison with PMDA-4,4'-ODA, PMDA-3,4'-ODA showed a much higher stress despite its slightly lower thermal expansion coefficient. This leads to the conclusion that the large difference between the stresses of the isomers results from the large difference in their moduli (5.0GPa for PMDA-3,4'-ODA and 3.0 GPa for PMDA-4,4'-ODA ). This behaviour is further supported by the difference in morphological structures of these two isomers as determined by wide-angle X-ray diffraction: PMDA-3,4'-ODA showed a well-developed crystalline structure, whereas the PMDA-4,4'-ODA did not. In addition, the interfacial adhesion between polyimide film and Si wafer primed with All00 was investigated.

Детальніше...  

We examine the problem of a highly polydisperse polymer melt within the framework of the tube model. Recent ideas on tube dilation in branched polymers are applied to linear melts when polydispersity is very strong. The weight distribution function P (M) and the relaxation modulus G (t) are related by a non-linear integral equation. The case of power-law polydispersity, P (M) ~ M-', is examined in detail and relaxation moduli, G(t), calculated. When 1 < r < 2, G(t) ~ t -2~ where 7 is related to the polydispersity index z via = (z- 1)/(2- z)

Детальніше...  

A number of approaches for the prediction of polymer-polymer miscibility have been reviewed. Much work, reported in the literature, has been directed towards understanding the behaviour of polymer and copolymer mixtures using polymer interaction parameters based on empirical or semi-empirical values. These values often require extensive experimental data for their calculation and tend to lack general applicability. A new concept is presented here that is based upon the utilization of the individual component contributions to the solubility parameter. The development of a 'miscibility parameter', which describes the interaction of polymer repeat units, provides semi-quantitative values which relate the three basic interactive forces, i.e. dispersive, polar and hydrogen bonding. This results in a generalized scheme applicable to large classes of systems. The validity of the miscibility parameter is tested against other methods described in the literature with good results

Детальніше...  

In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. Previous work characterized the effects of factors such as weld frequency, weld pressure, and weld time on the welding process and weld strength, and showed that the most important factor affecting weld strength of neat resins is the weld penetration--the decrease in the distance between the parts being welded that is caused by lateral outflow of material in the molten film. This paper is concerned with strengths of vibration-welded butt joints of polycarbonate- poly(butylene terephthalate) blends. Weld strengths were mapped at room temperature and at -29°C at strain rates of 0.25 x 10 -2 S-1 and 0.25 s-1. It was possible to achieve weld strengths equal to that of the base material. Tests on two blends showed that the low-temperature and high-strain-rate strengths and strains at failure can be significantly improved by changing the content of impact modifiers.

Детальніше...  

Корисні статті

Інженер-конструктор

Хто такий інженер-конструктор? Даним питанням задаються багато людей, які бажають пов'язати своє життя з цією професією. Варто відзначити, що ця професія однією з найбільш високооплачуваних на сучасному ринку праці, яка характеризується високим попитом з боку роботодавців. Інженер-конструктор машинобудування повинен володіти аналітичним складом розуму, підвищеною уважністю до деталей і відповідальним підходом до роботи. Дана діяльність пов'язана з прорахунками і різноманітним обладнанням. Першокласний інженер-конструктор механік володіє також такими рисами характеру, як раціональність і ерудованість. Важливу роль відіграє стресостійкість, адже робочий процес є досить трудомістким і при потребі замовника вимагає готовності швидко вносити зміни в готові креслення.

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.

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.

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.

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.