Epoxy polymerization

Several mechanisms for the polymerization of vinyl ether and epoxies have been suggested [20,22,23,25,27,28,33-35]. On irradiation with gamma rays or electrons, pure epoxies polymerize via a cationic mechanism [35]. However, this cationic polymerization is inhibited by just traces of moisture, as shown below for cyclohexene oxide in reaction 5. 

An analogous mechanism should also produce polymers on irradiation of epoxies. Crivello s recent mechanistic suggestions [29] are consistent with the mechanisms given above. One can conclude that radiation-induced polymerization of epoxies can proceed via several mechanisms. However, further work is needed to determine the relative contributions of the different mechanisms, which might vary from one epoxy to another. As part of the Interfacial Properties of Electron Beam Cured Composites CRADA [37], an in-depth study of the curing mechanism for the cationic-initiated epoxy polymerization is being undertaken. 

A Kinetic Study of an Anhydride-Cured Epoxy Polymerization... 

Cement hydration and epoxy polymerization occur simultaneously to form a structure that is similar to the latex-modified cementitious system. Epoxy systems develop high strength, adhesion and have low permeability, good water resistance and chemical resistance. A major advantage of this system is that it can be cured under moist or wet conditions. According to a recent study, the epoxy-modified mortars can be made without the hardeners with superior properties to those obtained with conventional epoxy mortars [89, 90]. 

A Lewis base is a compound that contains an unshared pair of electrons capable of undergoing chemical reactions. Tertiary amines are examples of Lewis bases, and often are used in epoxy curing agents. In an anionic epoxy polymerization the propagating species is the alkoxide anion generated by the reaction of the Lewis base with an epoxy ring. 

A novel approach to IPN synthesis was reported by Sperling and Arnts (I). They synthesized two polymer networks by simultaneous yet independent reactions in the same container at the same time. Complicated interactions were eliminated in the SIN s by combining free radical (acrylate) and condensation (epoxy) polymerization. The present work uses the basic technique of Sperling and Amts. 

Thermodynamic data of the epoxy polymerization with triphenylsulfonium salt photoinitiators can be obtained by differential scanning calorimetric measurements (DSC). Figure 6 shows the DSC diagram of the polymerization of Bisphenol-A di-glycidylether with triphenylsulfonium hexafluorophosphate, irradiation being carried... 

An egulvalence between the exotherms for the epoxy-amine addition and the epoxy-epoxy polymerization reaction simplifies the interpretation of data and permits the direct comparison of TGMDA resins having gulte different compositions. For TGMDA/DDS reactions, increasing the epoxy/amine eguivalent ratio -... 

For these studies it was desirable to maintain a constant temperature of about 22 C (room temperature). Since the amine-epoxy polymerization is an exothermic process, the syringes must have sufficient surface area to dissipate the evolved heat rapidly. Tests with Leeds and Northrup Potentiometer and a small alumel-chromel thermocouple, inserted into the center of the syringe, showed a maximum temperature rise of less than 2 C during the entire reaction time. This was sufficiently small to assume that isothermal conditions were maintained. 

Semi-batch epoxy polymerization Simultaneous maximization of number-average molecular weight and minimization of reaction time. NSGA-11 The MOO problem includes a constraint on the desired polydispersity index. Mitnetal. (2004a)... 

Deb, K., Mitra, K., Dewri, R. and Majumdar, S. (2004). Towards a better understanding of the epoxy-polymerization process using multi-objective evolutionary computation, Chem. Eng. Sci., 59, pp. 4261-4277. 

Majumdar, S., Mitra, K. and Raha, S. (2005a). Optimized species growth in epoxy polymerization with real-coded NSGA-II, Polymer, 46, pp. 11858-11869. 

Mitra, K., Majumdar, S. and Raha, S. (2004a). Mnlti-objective d3mamic optimization of a semi-batch epoxy polymerization process, Comput. Chem. Eng., 28, pp. 2583-2594. 

Although epoxy novolac resins are used in the present work, there is a fundamental difference from conventional encapsulant resins in that onium compounds in combination with copper acetyl(acetonate) are used in our materials as catalyst systems (2). These catalyst systems promote epoxy/epoxy polymerization and eliminate the need for hardeners. 

Crivello has published extensively on onium compounds and their function as catalysts (3,4). Generally, such compounds are photocatalysts, but are stable in the absence of light. Irradiation at the proper wavelength leads to a complex photodecomposition of the onium ion in which reactive cation radicals and neutral radicals are formed as short lived intermediates. Also formed are acids, corresponding to the anion of the onium compound, which catalyze the epoxy polymerization. Equations 2 and 3 show the decomposition of iodonium cations. 

As expected, the reaction exothems from our experiments with polyfunctional urethane acrylate systems are much more complex than those found with the cationic epoxy polymerizations. Figure 5 shows results from our aliphatic triacrylate DSC runs at three temperatures under continuous illumination. 

T. Wang, et al., Several ferrocenium salts as efficient photoinitiators and thermal initiators for cationic epoxy polymerization. J. Photochem. Photobiol. A Chem. 2007, 187(2-3), 389-394. 

T. Wang, B.S. Li, and L.X. Zhang, Carbazole-bound ferrocenium salt as an efficient cationic photoinitiator for epoxy polymerization. Polym. Int. 2005, 54(9), 1251-1255. 

Plasticizers can be classified as either solvent type (primary) or nonsolvent or poor solvent type (secondary). A special category of the nonsolvent type would include polymeric and epoxy polymeric plasticizers. 

AlNel. [Advanced Refractory Tech.] Aluminum nitride filler for elastomeric, epoxy, polymeric, and other... 

For scratch resistance improvement of organic surfaces also nano-composites are of interest. In a composite nano-scale boehmite or y-aluminia particles of about 15 nm diameter have been used as catalysts for epoxy groups linked to hydrolyseable and condensable silanes. Epoxy polymerization preferably takes place around the nanoparticles and additionally =Si-0-Al= bonds are formed between the silanes and the alumina surface [486]. It seems that the nano-particles, only 5% in volume fraction, are flexibly suspended in an inorganic-organic network. Such systems can be produced as transparent coatings and cured at relatively low temperatures of 90 to 120°C to high performance scratch resistant layers. 

Uses As semiconductor in electronics nitriding of steel filler for elastomeric, epoxy, polymeric systems, in coatings integrated circuit housing ceramics... 

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