Solvents attack

Film or fibers derived from low molecular weight polymer tend to embrittle on immersion ia acetone those based on higher molecular weight polymer (>0.60 dL/g) become opaque, dilated, and elastomeric. When a dilated sample is stretched and dried, it retains orientation and is crystalline, exhibiting enhanced tensile strength. The tensile heat-distortion temperature of the crystalline film is iacreased by about 20°C, and the gas permeabiUty and resistance to solvent attack is iacreased. 

Reactivities of several chlorinated solvents, including chloroform, with aluminum, iron, and 2inc in both dry and wet systems have been deterrnined, as have chemical reactivities in oxidation reactions and in reactions with amines (11). Unstabilized wet chloroform reacts completely with aluminum and attacks zinc at a rate of >250 //m/yr and iron at <250 //m/yr. The dry, uiiinhibited solvent attacks aluminum and zinc at a rate of 250 )J.m/yr and iron at 25 ]lni / yr. 

Resistant to alkalis, most organic solvents Attacked by acids... 

A variety of solvents have been used successfully. Extensive hydrolysis or alcoholysis may accompany reduction in aqueous or alcoholic solvent, attack presumably occurring on the intermediate vinyl ether (SS). 

Barrier Coat a coating used to isolate a paint system from the surface to which it is applied in order to prevent chemical or physical interaction between them, e.g. to prevent the paint solvent attacking the underlying paint or to prevent bleeding from underlying paint or material. 

This would accomplish substitution of Y for X by a potentially associative solvent attack followed by a fast replacement of solvent. This interpretation of the ki path is strongly supported by two lines of evidence. 

In fact, the analogy between the mechanisms of heterolytic nucleophilic substitutions and electrophilic bromine additions, shown by the similarity of kinetic substituent and solvent effects (Ruasse and Motallebi, 1991), tends to support Brown s conclusion. If cationic intermediates are formed reversibly in solvolysis, analogous bromocations obtained from bromine and an ethylenic compound could also be formed reversibly. Nevertheless, return is a priori less favourable in bromination than in solvolysis because of the charge distribution in the bromocations. Return in bromination implies that the counter-ion, a bromide ion in protic solvents, attacks the bromine atom of the bromonium ion rather than a carbon atom (see [27]). Now, it is known (Galland et al, 1990) that the charge on this bromine atom is very small in bridged intermediates and obviously nil in /f-bromocarbocations [28]. 

An ethanolic solution of the hypnotic, methyprylone (269), was irradiated with simulated sunlight [164]. Solvent attack and ring opening gave the amidoester (270) [165]. 

An unusual kinetic result has been reported51 when phenylhydroxylamine reacted anaerobically with bisulphite anion. The product distribution was as expected, i.e. both 2- and 4-aminophenol and the 2- and 4-aminobenzenesulphonates were formed. Kinetic measurements showed a first-order dependence upon [bisulphite], in contrast to the earlier work with Cl- and later with N3 -. The authors propose a mechanism involving direct attack by the nucleophile at the 2- and 4-positions as the rate-limiting step, followed by proton transfers and solvent attack to form the sulphonate products. 

N-Donor Ligands. The full account of the crystal structure of [Mo02(8-hydroxyquinolate)2] has been published. The dimensions of the M0O2 unit are O—Klo—O = 104.C and Mo—O = 171(2) pm. The electrochemistries of this and the related molybdenum(v) complex. [ MoO(8-hydroxyquino-late)2 2 0], have been investigated as simple models of molybdenum-fluoro-protein enzymes (p. 146). Reduction of the molybdenum(vi) complex occurs in two one-electron steps with solvent attack of the reduced intermediates and displacement of the 8-hydroxyquinolato-groups. ... 

Five mechanisms are possible for this process (Scheme 3) direct alcohol attack at C-1 after 0-1 protonation (A) the related two stage process by way of a cyclic carbonium ion (B) solvent attack at C-1 after ring... 

The reaction of the organic halide with magnesium is carried out in a non-protic polar solvent, usually diethyl ether or THF. Typical by-products are RR, RH and R(-H) (alkene), resulting from coupling and disproportionation reactions of the organic moiety. Also, by-products resulting from solvent attack are sometimes formed, but usually to a lesser extent. 

Solvent-Based Adhesives—In these the adhesive flows because it is dissolved in an appropriate solvent, and solidification occurs on evaporation of the solvent. Good bonds are usually formed if the solvent attacks or actually dissolves some of the plastic adherend to produce a solvent-welded bond. 

Besides prinfing and decoration, flexographic, gravure, and lifhographic plates as well as silk screens are used in resist chemistry, which is widely employed in the production of printed circuit boards. A resist is a material that will resist solvent attack. A negative resist is a material that, upon exposure to light cross-links, becomes less soluble in a solvent system that would... 

The catalysis may not depend on the configuration of the oxime, since both syn and anti function with similar efficacy138. For this reason a mechanism involving the oxime anion acting as a general base catalyst for solvent attack has been favored. However, the observed large rate enhancement is more in accord with a cyclization mechanism, and, until an anti-syn interconversion prior to hydrolysis can be unequivocally eliminated, the direct attack of the oximate anion on phosphorus remains a strong possibility. 

In other words, the form of the rate law does not help one distinguish between an A (or /a) and 0 (or Id) mechanism for the kx pathway. The ambiguity in the interpretation of the kt term has caused much discussion and experimentation. It is found that reactions take place faster in more nucteopbilic solvents, suggesting that solvent attack plays an important role. 

The crystallinity of the pary lenes determines two of their most important practical characteristics mechanical strength at elevated temperatures and solvent resistance. The crystallinity of parylenes is confined to small-submicromctcr domains that arc randomly dispersed throughout an amorphous continuum. Because the crystalline domains are much more resistant to permeation than the amorphous phase, they retain their reinforcing structural role even in the presence of permeants in the amorphous phase, thus giving the parylenes dieir resistance to solvent attack. 

Several analytical techniques have been used to characterize the polymer/ silane coupling agent interphase. Culler et aL [2] used Fourier transform infrared (FT-IR) spectroscopy to characterize the chemical reactions at the matrix/silane interphase of composite materials. They correlated the extent of reaction of the resin with the coupling agent (as determined by FT-IR) with the extent of interpenetration. Culler et al. [2] have also used observations of improved resistance of the interphase region to solvent attack as indirect evidence to support the interpenetrating network theory. 

Product The product from solvent attack on the carboninm ion 82 must be from the exo direction since the endo side would be hindered by the three-center e3 bon32 ... 

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