Temperature stable polymers

Aromatic units Temperature-stable Polymer class bond... 

Both poly(1,4-oxyphenyiene) and poly(1,3-oxyphenylene) are temperature stable polymers and are used as high temperature stable fluids. Other poly(substituted oxyphenylenes) are also temperature stable and are used for purposes that require... 

Silicones, as a class, are rated among the highest temperature stable polymers. They can withstand temperatures of 200 °C, almost continuously, without degradation of physical or electrical properties and have been used at temperatures as high as 300 °C. Because of their high thermal stabilities, they are used as adhesives and encapsulants for electronic modules that are expected to perform in extreme temperature environments, such as near automotive engines and in deep-well sensors. Because of their low moduli of elasticity, silicones also fare well at very low temperatures. They are rated for continuous use at —80 °C, but may be used at even lower temperatures. 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

Polyquinolines are some of the most versatile thermally stable polymers they were developed during the 1970s in response to increasing demand for high temperature resistant materials and are undergoing commercial development (Maxdem, Inc., San Dimas, California). Evidence of their stabiUty is... 

Acrylate and acrylamide polymers have several uses in drilling fluids, one of which is for filtration control. Sodium polyacrylates [9003-04-7] having molecular weights near 250,000 are exceUent temperature-stable filtration control agents for both fresh- and salt water muds, provided the concentration of water-soluble calcium is <400 mg/L (83). The calcium ions are precipitated using a carbonate such as soda ash, before adding the polyacrylate at concentrations up to ca 6 kg/m (3 Ib/bbl). 

Mold temperature can vary widely. Typical temperatures range from 40 to 150°C. Higher mold temperatures favor polymer crystallisation and result ia more dimensionally stable parts. Crystallinity can be developed ia parts molded ia cold molds by annealing at approximately 200°C. 

Anionic Polymerization of Cyclic Siloxanes. The anionic polymerization of cyclosiloxanes can be performed in the presence of a wide variety of strong bases such as hydroxides, alcoholates, or silanolates of alkaH metals (59,68). Commercially, the most important catalyst is potassium silanolate. The activity of the alkaH metal hydroxides increases in the foUowing sequence LiOH < NaOH < KOH < CsOH, which is also the order in which the degree of ionization of thein hydroxides increases (90). Another important class of catalysts is tetraalkyl ammonium, phosphonium hydroxides, and silanolates (91—93). These catalysts undergo thermal degradation when the polymer is heated above the temperature requited (typically >150°C) to decompose the catalyst, giving volatile products and the neutral, thermally stable polymer. 

Materials of these types have T s of some 290-300°C and some grades are claimed to be stable to about 400°C. Whilst resistant to hydrocarbons, halogenated hydrocarbons, ethers and acids the polymers are soluble in such materials as dimethylformamide, N-methylpyrrolidone and pyridine. Bases can cause stress cracking. These non-crystalline polymers are tough at temperatures as low as -46°C whilst at 260°C they have the strength shown by PTFE at room temperature. The polymers also exhibit excellent electrical insulation properties. 

NOTE All-polymer programs employ various types of organic deposit control agents (DCA) such as phosphinocarboxylic acid (PCA) products, which tend to be high temperature-stable sludge dispersants, crystal modifiers, and hardness transporters. 

Equilibrium between Monomer and Polymer. A monomer-with-polymer equilibrium is quite different from the polymer-with-condensation-product equilibrium discussed in Section 13.1.1. If the condensation product is removed from the reaction mixture, a condensation polymer increases in molecular weight. If the monomer is removed when it is in equilibrium with the polymer, the polymer depolymerizes to re-form the monomer. At temperatures suitable for long-term use, the equihbrium will be shifted toward stable polymer. However, at fabrication temperatures and at the high temperatures common in devolatilization, the production of monomer and low-molecular-weight ohgomers can be significant. 

A tetrapolymer consisting of 40 to 80 mole-percent of AMPS, 10 to 30 mole-percent of vinylpyrroMone, 0 to 30 mole-percent of acrylamide, and 0 to 15 mole-percent of acrylonitrile was also a suggested as a fluid loss additive [1061]. Even at high salt concentrations, these polymers yield high-temperature-stable protective colloids that provide for minimal fluid loss under pressure. 

C. J. Bemu. High temperature stable modified starch polymers and well drilling fluids employing same. Patent EP 852235,1998. 

Organic polymers have been used to increase the viscosity of acids. The primary application is in fracture acidizing. Binary and ternary acrylamide copolymers are the most commonly used chemicals for this application. Many of these polymers degrade rapidly in strong acids at temperatures >130 F development of more stable polymers suitable for high temperatures is desirable. Recently developed polymers for this application include acrylamide copolymers with ... 

Norman, L.R., Conway, M.W. and Wilson J.M. "Temperature Stable Acid Gelling Polymers. Laboratory Evaluation and Field Results," SPE paper 10260, 1981 SPE Annual Fall Technical Conference and Exhibition of AIME, San Antonio, October 5 7. 

The second consideration, anticipated in Sect. 3.1, is that whereas Sm and Sc increase little with temperature (see Fig. 8) so that in the literature the temperature dependence of Gc and Gm is often approximated by straight lines, Sl varies moderately up to the glass transition temperature Tg but will increase substantially between Tg and the isotropization temperature. The behavior of Sl is due to the fact that, as the temperature increases, polymer chains are progressively more likely to bend sharply in the melt, whereas they are forced to remain straight in the mesophase and in crystals. The downward curvature of Gl in Fig. 8 shifts to lower temperatures with inherently more flexible chains. With very flexible polymers Tml becomes therefore smaller than the crystal-melting temperature Tcl and a stable mesophase cannot form. 

Au is the difference between the liquid and glassy volumetric expansion coefficients and the temperatures are in kelvin. "The WLF equation holds between I], or / f 10 K and abftut 100 K above 7A,. Above this temperature, for thermally stable polymers, Berry and Fox (28) have shown that a useful extension of the WLF equation is the addition of an Arrhenius term with a low activation energy. 

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