Academic literature on the topic 'Ethers. Urea'

Random copolymers are prepared by the copolymerization of a mixture of cyclic oligomers. Although the resulting polymer can be quite blocky (figure 8.1), taking the reaction to equilibrium can give a polymer that is essentially random in its chemical sequencing. One reason for preparing copolymers is to introduce functional species, such as hydrogen or vinyl side groups, along the chain backbone to facilitate cross linking. Another reason is the introduction of sufficient chain irregularity to make the polymer inherently noncrystallizable. Specific examples of comonomers include imides, perylenediimide, urethane-ureas, epoxies, other siloxanes, amides, styrene, divinylbenzene, acrylics, silsesquioxanes, polythiophenes, and poly(lactic acid). One novel combination is the preparation of polysiloxanebased episulfide resins. An unusual application is the use of monomethylitaconate- grafted polymethylsiloxane to induce crystal growth of CaCO3. Polysiloxanes containing thermally curable brenzoxazine moieties in the main chain are also in the category. These and other copolymers have been extensively characterized by nuclear magnetic resonance (NMR) spectroscopy. The sequential coupling of functionally terminated chains of different chemical structure can be used to make block copolymers, including those in which one or more of the blocks is a polysiloxane. If the blocks are relatively long, separation into a two-phase system invariably occurs. Frequently, one block will be in a continuous phase and the other will be dispersed in domains having an average size the order of a few hundred angstroms. Such materials can have unique mechanical properties not available from homopolymer species. Sometimes similar properties can be obtained by the simple blending of two or more polymers. Examples of blocks used with polydimethylsiloxane (PDMS) include imides, epoxies, butadienes, ε-caprolactones, amides having trichlorogermyl pendant groups, urethanes, ureas, poly(ethylene glycols), polystyrene, vinyl acetates, acrylates or methacrylates, 2-vinylpyridine, and even other polysiloxanes. Some results have also been reported for polyesters, polyethers, hydroxyethers of bisphenol A, bisphenol A arylene ether sulfones, vinylpyridinebenzoxazines, methyloxazolines, terpyridines, polysulfones, γ-benzyl-Lglutamate, and carboranes. Two other examples are foamed polypropylene and melamine resins. Even ABA, ABC triblock copolymers, and ABCBA pentablock copolymers involving PDMS have been reported.

Andrey P. A ntonchick of the Max-Planck-Institut Dortmund devised (Org. Lett. 2012, 14, 5518) a protocol for the direct amination of an arene 1 to give the amide 3. Douglass A. Klumpp of Northern University showed (Tetrahedron Lett. 2012, 53, 4779) that under strong acid conditions, an arene 4 could be carboxylated to give the amide 6. Eiji Tayama of Niigata University coupled (Tetrahedron Lett. 2012, 53, 5159) an arene 7 with the α-diazo ester 8 to give 9. Guy C. Lloyd-Jones and Christopher A. Russell of the University of Bristol activated (Science 2012, 337, 1644) the aryl silane 11 to give an intermediate that coupled with the arene 10 to give 12. Ram A. Vishwakarma and Sandip P. Bharate of the Indian Institute of Integrative Medicine effected (Tetrahedron Lett. 2012, 53, 5958) ipso nitration of an areneboronic acid 13 to give 14. Stephen L. Buchwald of MIT coupled (J. Am. Chem. Soc. 2012, 134, 11132) sodium isocyanate with the aryl chloride 15 (aryl triflates also worked well) to give the isocyanate 16, which could be coupled with phenol to give the carbamate or carried onto the unsymmetrical urea. Zhengwu Shen of the Shanghai University of Traditional Chinese Medicine used (Org. Lett. 2012, 14, 3644) ethyl cyanoacetate 18 as the donor for the conversion of the aryl bromide 17 to the nitrile 19. Kuo Chu Hwang of the National Tsig Hua University showed (Adv. Synth. Catal. 2012, 354, 3421) that under the stimulation of blue LED light the Castro-Stephens coupling of 20 with 21 proceeded efficiently at room temperature. Lutz Ackermann of the Georg-August-Universität Göttingen employed (Org. Lett. 2012, 14, 4210) a Ru catalyst to oxidize the amide 23 to the phenol 24. Both Professor Ackermann (Org. Lett. 2012, 14, 6206) and Guangbin Dong of the University of Texas (Angew. Chem. Int. Ed. 2012, 51, 13075) described related work on the ortho hydroxylation of aryl ketones. George A. Kraus of Iowa State University rearranged (Tetrahedron Lett. 2012, 53, 7072) the aryl benzyl ether 25 to the phenol 26. The synthetic utility of the triazene 27 was demonstrated (Angew. Chem. Int. Ed. 2012, 51, 7242) by Yong Huang of the Shenzen Graduate School of Peking University.

As it is envisioned today, the first segment of the UREX+ process uses low nitric acid concentrations for U(VI) extraction where pertechnetate anion, TcO4−, can be co-extracted with the uranyl and nitrate into TBP-hydrocarbon solutions. A reductant complexant, acetohydroxamic acid (AHA) is added to the process through the scrub to limit the extractability of plutonium and neptunium. Recent work performed in our laboratory (Ref. 1) demonstrated that TcO4− undergoes reductive nitrosylation by AHA under a variety of conditions. The resulting divalent technetium is complexed by AHA to form the pse

Corrosion is one of the critical causes of material loss in metal components. This research is focused on the synthesis, and electrochemical properties of polyelectrolyte layered microcapsules (PMCs) reinforced smart polymeric coating for corrosion protection of steel substrates. For this purpose, monolayer urea-formaldehyde microcapsules encapsulated with linalyl acetate (MLMCs) was synthesized by Insitu polymerization. In the next step, phenylthiourea (PTU) was loaded between the layers of polyelectrolytes; polyethylenimine (PEI) & sulfonated polyether ether ketone (SPEEK) on the surface