Substitution anhydride groups

Monomer Reactivity. The poly(amic acid) groups are formed by nucleophilic substitution by an amino group at a carbonyl carbon of an anhydride group. Therefore, the electrophilicity of the dianhydride is expected to be one of the most important parameters used to determine the reaction rate. There is a close relationship between the reaction rates and the electron affinities, of dianhydrides (12). These were independendy deterrnined by polarography. Stmctures and electron affinities of various dianhydrides are shown in Table 1. 

This break on either side is important for anhydrides with different R groups. The cleavc e of the N-R bond is important for amides with N-substituted alkyl groups. A primciry cimide usually has a strong peak at m/e 44, which corresponds to [0=C=NH2] ... 

The resistance of polymers to flame may be increased by the addition of halogenated compounds and antimony oxide. Organic phosphate additives inhibit the glow of the char formed in burning polymers. Polymers with chlorine pendant groups, such as PVC, and those with halogen-substituted phenyl groups, such as polyesters produced from tetrabromophthalic anhydride, are more flame-resistant than hydrocarbon polymers. 

The propagation involving the activated monomer-anion is possible only for the non-N-substituted NCA s — the N-substituted anhydrides cannot form such ions. Hence, if the polymerisation initiated by aprotic bases proceeds entirely by this route, no N-substituted NCA may be polymerised by these initiators [see however references (102), (103) and (104)]. Therefore, Bamford s group spared no effort to prove the validity of this statement and their elegant experiments deserve detailed discussion. 

Irradiation of the substituted cyclohexadiene resulted in the formation of the Dewar benzene skeleton by a disrotatory ring closure. Reaction with lead tetraacetate (a reaction that is not covered in this book) was used to remove the anhydride group and introduce the final double bond of Dewar benzene. Again, because of the forbidden nature of the conrotatory opening to benzene, Dewar benzene has an appreciable lifetime. At 25°C the half-life for its conversion to benzene is 2 days, and at 90°C its half-life is 30 min. 

The reaction apparently proceeds by the electrophilic attack of an acylium ion or protonated mixed anhydride [ArCO(H)OS02CF3], upon the para-position of an aromatic ether (Fig. 37). Loss of a proton results in the formation of 256. The nonsubstituted aryl group of the diphenyl ether was found to be much less reactive toward electrophilic substitution. This group is deactivated by protonation of the keto group in the strongly acidic environment. Therefore, monomers must be designed so that this type of resonance effect does not inhibit substitution at the second site of substitution [Eq. (53)] [162]. 

It was known in the early 70 s that unsymmetrically substituted anhydrides and im-ides can undergo highly regioselective transformations, e.g. to lactones and lactams, respectively (see Scheme 6.23) [166]. The growing importance of such products as synthetic intermediates raised the issue of control of regioselectivity, and several authors attempted to identify the factors at play [167-169]. The emphasis was on metal hydride reductions of succinic anhydrides to y-lactones, and succinimides to hydroxypyrrolidinones. Suess [167], Rosenfield and Dunitz [47], and independently Kayser and Morand [169], proposed that the approach of a nucleophile to the less substituted carbonyl group can actually be more hindered if there is indeed a strong preference for rearside attack. The two pathways are compared in Scheme 6.24. 

Replacement of nitro by azido groups. — Ar. nucleophilic substitution activated by o-dicarboxylic acid anhydride groups. 3-Nitrophthalic anhydride heated with Na-azide at 110° in dimethyl-formamide, quenched in water, and acidified 3-azidophthalic acid. Y t Also replacement of chlorine... 

The NMR spectrum for zein in Figure 2 showed aromatic peaks in the region of 7.5-8.0 ppm., representing aromatic protons of benzoate group. The IR spectrum of the zein derivative in Figure 3 showed evidence of the ester linkage as a pronounced shoulder at 1731 cm on the amide I peak of the zein. Evidence of the reaction of benzoic anhydride with the zein also appeared at 714 cm from the mono-substituted benzene group in the derivative. 

Radical substitution of the hydrogen from the methyl groups PHj OH,X Kl( -HY CH3 X CH, hc=ch X-Y = Br-Br,C1-C1 (12) RS0.-C1 (13) I 1 ( ) Halogenation, sulfonation, binding of maleric anhydride group, unsaturated carboxyl acids, amides, imides, esters, epoxides, amines, alcohol can be used Product of (12) is precursor for PCMs, that of (13) for direct PCMs. 

The present paper reports the ring-opening polymerization of norbornene derivatives substituted by nitrile, amide, imide, ester, pyridyl and acid anhydride groups by the above-mentioned catalysts. The polymerization behavior of these monomers and the physical properties of the polymers of norbornenenitriles will be described. 

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