Dichloromethane polymerization

Controlled polymerization of LA catalyzed by TfOH, in the presence of an alcohol initiator (ROH), was also described by Bourissou et and Basko and Kubisa. The solvent for polymerization was somewhat restricted to dichloromethane, toluene being a poor solvent of PLA and THF being polymerized by TfOH. In dichloromethane, polymerization proceeded at 25-35 °C within hours for a typical [ROH]/[cat] between 0.5 and 1, with various initiators, including H2O, TPrOH, PrOH, and pentan-l-ol (entries 7 and 8). Other catalysts such as CF3COOH and HCl in the presence of i-PrOH were found completely ineffective for LA polymerization, under identical conditions. LA was thus found much less... 

Diaza-l 8-crown-6 has also been converted into polymeric materials by the reaction of 9 with toluenediisocyanate . The polymeric materials were prepared by stirring commercially available 9 with TDI in dichloromethane solution. Reaction was rapid and exothermic, but the mixture was not worked up until the next day. The product was a white solid which softened between 170—190° and decomposed between 250—270°. 

Recently, Deligoz and Yilmaz [24,25] described the preparation of two polymeric calix[4]arene tetra esters (Scheme 4) and their Na -complexation. Based on phase-transfer experiments with these compounds using alkali picrates in water-dichloromethane, they confirmed that polymers are as Na selective as monomers. 

Chloro-l//-l-benzazepines 2 are obtained as unstable red oils in excellent yields by heating 1 //-l-benzazepin-2(3//)-ones 1 with phosphoryl chloride in pyridine.208 Reaction conditions are important since in the absence of pyridine, or in dichloromethane solution, only poor yields of dimers, e.g. 3, are produced. The chlorobcnzazepines are stable for only short periods (24 hours in anhydrous pyridine) and rapidly polymerize. Isolation of the pure chloro compounds is difficult since they undergo very rapid hydrolysis to the benzazepinones. 

C. Polymeric Garbodiimide. The polymeric urea prepared above (9.09 g.) is combined with 100 ini. of dichloromethane in a 300-ml., thrce-ncckcd, round-bottomed flask equipped with a magnetic stirrer, a condenser fitted with a gas-inlet tube, and a stopper. Under a blanket of nitrogen, 5.76 g. (0.057 mole) of triethylamine [Ethanamine, N,N-... 

Penta-1,3-diyne (Methyldiacetylene). CH3.CiC.CiCH mw 65.10 OB to C02 —294.93% liq mp —4.5 to -38.5° bp 76-77° (explds at atm press), 45° at 140mm d 0.7909 g/cc at 20/4° RI 1.4762 (Ref 3) and 1.4817 (Ref 1). Sol in ethanol and petr with a bp > 180°. Prepn is by reacting monosodium-acetylenide with dichloromethane in liq ammonia at 20 to 40°, followed by treatment with ammonium chloride. The product is stable in the dark at -35° but polymerizes readily at above —20° in the light. Penta-1,3-diyne forms two expl salts Copper penta-1,3-diyne, CuCsH3, dark yel ndls/by reaction with CuCl, explds on shock or by rubbing and Silver penta-1,3-diyne, yel-brn ndls, by reaction with aq silver nitrate in ammonium hydroxide, a v expl compd Refs 1) Beil 1, [247], 1057 <1117)... 

Polymerization of 4-bromo-6,8-dioxabicyclo[3.2.1 ]octane 2 7 in dichloromethane solution at —78 °C with phosphorus pentafluoride as initiator gave a 60% yield of polymer having an inherent viscosity of 0.10 dl/g1. Although it is not described explicitly, the monomer used seems to be a mixture of the stereoisomers, 7 7a and 17b, in which the bromine atom is oriented trans and cis, respectively, to the five-membered ring of the bicyclic structure. Recently, the present authors found that pure 17b was very reluctant to polymerize under similar conditions. This is understandable in terms of a smaller enthalpy change from 17b to its polymer compared with that for 17a. In the monomeric states, 17b is less strained than 17a on account of the equatorial orientation of the bromine atom in the former, whereas in the polymeric states, the polymer from 17b is energetically less stable than that from 17a, because the former takes a conformation in which the bromine atom occupies the axial positioa Its flipped conformation would be even more unstable, because the stabilization by the anomeric effect is lost, in addition to the axial orientation of the methylene group. 

Polymeric sulfur obtained from Crystex after extraction with dichloromethane followed by drying in a vacuum [180]... 

Quaternary ammonium azides will displace halogens in a synthesis of alkyl azides. Dichloromethane has been used as a solvent, although this can slowly form diazido-methane which may be concentrated by distillation dining work-up, thereafter easily exploding [1]. An accident attributed to this cause is described, and acetonitrile recommended as a preferable solvent, supported polymeric azides, excess of which can be removed by filtration are also preferred in place of the tetrabutylam-monium salt [2]. A similar explosion was previously recorded when the quaternary azide was generated in situ from sodium azide and a phase transfer catalyst in a part aqueous system [3,4],... 

The most industrially significant polymerizations involving the cationic chain growth mechanism are the various polymerizations and copolymerizations of isobutylene. In fact, about 500 million pounds of butyl rubber, a copolymer of isobutylene with small amounts of isoprene, are produced annually in the United States via cationic polymerization [126]. The necessity of using toxic chlorinated hydrocarbon solvents such as dichloromethane or methyl chloride as well as the need to conduct these polymerizations at very low temperatures constitute two major drawbacks to the current industrial method for polymerizing isobutylene which may be solved through the use of C02 as the continuous phase. 

The formation of alkenes and alkene-related polymerization products can seriously reduce the yields of desired alkane products from secondary alcohols, which can undergo elimination reactions. For example, reduction of 2-octanol at 0° with boron trifluoride gas in dichloromethane containing 1.2 equivalents of tri-ethylsilane gives only a 58% yield of n-octane after 75 minutes (Eq. II).129 The remainder of the hydrocarbon mass comprises nonvolatile polymeric material.126... 

In 1977, Koo and Schuster studied the CL emission produced when diphe-noyl peroxide was decomposed at 24°C in dichloromethane in the dark producing benzocoumarin and polymeric peroxide [111, 112]. No CL emission was observed directly as benzocoumarin is nonfluorescent however, in the presence of aromatic hydrocarbons light was produced because of the fluorescence of these hydrocarbons. The explanation of this phenomenon was based on the above-mentioned CIEEL the aromatic hydrocarbons, which have a low oxidation potential, transfer one electron to diphenoyl peroxide to form a charge-transfer complex, from which benzocoumarin and the corresponding hydrocarbon in the excited state are produced (Fig. 13). 

Poly(styrene) and PMMA were synthesized from their respective monomers using azobisisobutyronitrile-initiated radical polymerization in benzene. Four freeze-pump-thaw cycles were used to degas the monomer solutions and polymerization was carried out for 48 hours at 60°C. The polymers were purified by multiple reprecipitations from dichloromethane into methanol. Films of these polymers were prepared and found to be free of any fluorescent impurity. 

In an effort to optimize the solvent-containing passive sampler design, Zabik (1988) and Huckins (1988) evaluated the organic contaminant permeability and solvent compatibility of several candidate nonporous polymeric membranes (Huckins et al., 2002a). The membranes included LDPE, polypropylene (PP), polyvinyl chloride, polyacetate, and silicone, specifically medical grade silicone (silastic). Solvents used were hexane, ethyl acetate, dichloromethane, isooctane, etc. With the exception of silastic, membranes were <120- um thick. Because silicone has the greatest free volume of all the nonporous polymers, thicker membranes were used. Although there are a number of definitions of polymer free volume based on various mathematical treatments of the diffusion process, free volume can be viewed as the free space within the polymer matrix available for solute diffusion. 

Along with homopolymerization, copolymerization has also been studied within the framework of initiation by tris(4-bromophenyl)ammoniumyl hexachloroantimonate (Bauld et al. 1998a). Generally, cation-radical cycloaddition occurs more efficiently when the reactive cation-radical is the ionized dienophile (Bauld 1989, 1992). In the cited work on copolymerization, the bis(diene) was chosen to be resistant against ionization by the initiator used. As to the dienophile functionality, propenyl rather than vinyl moieties were selected because terminal methyl groups sharply enhance the ionizability of the alkene functions. The polymerization shown in Scheme 7.18 was performed in dichloromethane at 0°C. 

Like its monomeric counterpart, the polymeric reagent is inert to simple amines, amides, alcohols and phenols, but easily oxidizes thiols to disulphides, phosphines to phosphine oxides, hydroquinone and catechol to quinones, and thioketones, thioesters and trithiocar-bonates to the corresponding 0x0 derivatives, in dichloromethane, chloroform or acetic... 

B. General Oxidation Procedure for Alcohols. A sufficient quantity of a 5% solution of dipyridine chromium (VI) oxide (Note 1) in anhydrous dichloromethane (Note 7) is prepared to provide a sixfold molar ratio of complex to alcohol. This excess is usually required for complete oxidation to the aldehyde. The freshly prepared, pure complex dissolves completely in dichloromethane at 25° at 5% concentration to give a deep red solution, but solutions usually contain small amounts of brown, insoluble material when prepared from crude complex (Note 8). The alcohol, either pure or as a solution in anhydrous methylene chloride, is added to the red solution in one portion with stirring at room temperature or lower. The oxidation of unhindered primary (and secondary) alcohols proceeds to completion within 5 minutes to 15 minutes at 25° with deposition of brownish-black, polymeric, reduced chromium-pyridine products (Note 9). When deposition of reduced chromium compounds is complete (monitoring the reaction by gas chromatography or thin-layer chromatography analysis is helpful), the supernatant liquid is decanted from the (usually tarry) precipitate and the precipitate is rinsed thoroughly with dichloromethane (Note 10). 

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