Monomers nitrobenzene

The homopolymerization ofl consists of a room-temperature reaction of the monomer dissolved in nitrobenzene in the presence of anhydrous ferric chloride. Polymerizations were carried out under a stream of dry nitrogen. As depicted in Scheme 2, the homopolymerization of 1 to form 6FNE takes place by means of the Scholl reaction. The mechanism of the Scholl reaction was assumed to proceed through a radical-cation intermediate derived from the single-electron oxidation of the monomer and its subsequent electrophilic addition to the nucleophilic monomer. The reaction releases two hydrogens, both as protons, to form the... 

In this case the inhibitor is nitrobenzene which adds on the growing chain P yielding a Polymer chain having a nitrobenzene endgroup carrying a radical site. The nitrocompound end of the chain is, resonance stabilised and the resonance-stabilised free-radical end is not active enough to attract a fresh monomer molecule and further propagate the chain. 

The last experimental work was aimed at measuring the propagation rate-constant, kp, for various monomers under the ideal conditions which, it was hoped, would be provided by the solvent nitrobenzene. This was frustrated by the complexing of the propagating carbenium ions with the solvent but the mechanistic insight resulting from a detailed examination of the results provided useful new understanding of previously unexplained anomalies. 

My last kinetic work was aimed at determining the kp+ of a range of monomers by what I believed to be a reliable method. For kinetic and electrochemical reasons I chose nitrobenzene as the solvent, and I chose carbenium and carboxonium salts as initiators so as to achieve a clean and fast initiation. The rate-constants were adequately reproducible, but it turned out that they were not the kp+. The project was flawed because I had been unaware of the reversible cationation of the solvent by the carbenium ions. A careful analysis of the kinetic, analytical and thermochemical results gave a new insight into the reaction mechanisms in nitrobenzene, but the main objective had eluded me. 

H20, temperature -30 °C to -95 °C) the initial rate of polymerisation of isobutene is proportional to the concentration of monomer, that of styrene proportional to the square of the monomer concentration [13], so that the same mechanism cannot apply to both monomers. Further, in the very system in which the Gantmakher and Medvedev mechanism would be most plausible styrene + SnCl4 + nitrobenzene [10] - the polymerisation is found to be of first order in monomer and not, as Gantmakher and Medvedev predict, of second order, and moreover depended on the presence of water. 

The last sentence of the paper under consideration here turned out to be illusory, because, as shown in Section 5.6, the rate-constants measured in nitrobenzene solution turned out to be not those for the attack of a carbenium ion on the double-bond of the monomer, but hybrids. 

This is the third report on attempts to measure the propagation rate constant, kp+, for the cationic polymerisation of various monomers in nitrobenzene by reaction calorimetry. The first two were concerned with acenaphthylene (ACN) [1, 2] and styrene [2]. The present work is concerned with attempts to extend the method to more rapidly polymerising monomers. With these we were working at the limits of the calorimetric technique [3] and therefore consistent kinetic results could be obtained only for indene and for phenyl vinyl ether (PhViE), the slowest of the vinyl ethers 2-chloroethyl vinyl ether (CEViE) proved to be so reactive that only a rough estimate of kp+ could be obtained. Most of our results were obtained with 4-chlorobenzoyl hexafluoroantimonate (1), and some with tris-(4-chlorophenyl)methyl hexafluorophosphate (2). A general discussion of the significance of all the kp values obtained in this work is presented. 

After the phial-magazine had been charged with the required phials, the calorimeter was evacuated for several hours if a volatile monomer was to be used it was distilled in, and the nitrobenzene was added from its reservoir. Then the jacket of the calorimeter was evacuated, the phial of monomer (if a monomer of low volatility was being used) was pushed into the breaker-tube and broken, and then the phial of initiator was pushed into the breaker-tube. When the temperature was constant (usually at 298 or 283 K), the phial of initiator was broken and the breaker dropped rapidly a second time to help the mixing-in of the initiator solution. 

Monomers. BTDA and APA were obtained from Gulf Chemicals. BTDA was recrystallized from acetic anhydride prior to use, and APA was distilled under reduced pressure. Diamines la-d were prepared from 1-fluoro-4-nitrobenzene and the appropriate glycol according to the known procedure (4). 

Uses Manufacture of ethylbenzene (preparation of styrene monomer), dodecylbenzene (for detergents), cyclohexane (for nylon), nitrobenzene, aniline, maleic anhydride, biphenyl, benzene hexachloride, benzene sulfonic acid, phenol, dichlorobenzenes, insecticides, pesticides, fumigants, explosives, aviation fuel, flavors, perfume, medicine, dyes, and many other organic chemicals paints, coatings, plastics and resins food processing photographic chemicals nylon intermediates paint removers rubber cement antiknock gasoline solvent for fats, waxes, resins, inks, oils, paints, plastics, and rubber. 

There are nine chemicals in the top 50 that are manufactured from benzene. These are listed in Table 11.1. Two of these, ethylbenzene and styrene, have already been discussed in Chapter 9, Sections 5 and 6, since they are also derivatives of ethylene. Three others—cumene, acetone, and bisphenol A— were covered in Chapter 10, Sections 3-5, when propylene derivatives were studied. Although the three carbons of acetone do not formally come from benzene, its primary manufacturing method is from cumene, which is made by reaction of benzene and propylene. These compounds need not be discussed further at this point. That leaves phenol, cyclohexane, adipic acid, and nitrobenzene. Figure 11.1 summarizes the synthesis of important chemicals made from benzene. Caprolactam is the monomer for nylon 6 and is included because of it importance. 

Table II. Lignin Monomer Composition, Obtained by Nitrobenzene Oxidation of Lignin from Normal and Brittle Fescue Grown at Lusignan (Same as in Table I)...

Tables IV and V show the monomer composition of lignins for both parietal and saponification residues. In this regard, comparison between PR and SR values allows the characterization of the lignin core, which is not solubilized after alkaline treatment (20,21). Instead of using nitrobenzene oxidation, thioacidolysis was used to characterize the non-condensed...

A100 ml flask is fitted with an adapter (see Sect. 2.2.5.3), flamed under vacuum using an oil pump, and filled with nitrogen. 5 ml of the prepared monomer mixture (see above) are pipetted in, followed by 40 ml of an initiator solution prepared from 50 ml of pure dry nitrobenzene (see Example 3-40) and 300 mg (2.25 mmol) of anhydrous aluminum trichloride.The flask is now removed from the adapter under a slight positive pressure of nitrogen and immediately closed with a ground glass stopper.The flask is briefly shaken and allowed to stand at room temperature for 1 h.The solution is then dropped into methanoi and the copolymer worked up as described above. Yield 40-50% with respect to the monomer mixture. 

Several polydentate SBs may act as binucleating ligands see Section 33.5.12.1. Only a few miscellaneous polydentate SBs will be included here. A complex with the SB obtained in the reaction of two moles of benzoyl hydrazide with acetylacetone had v(V=0) = 995 cm 1, Pea =1.7BM and was monomeric square pyramidal (117).792 A few complexes with the ethylenediamine derivatives of 2,2 -dihydroxychalcones (118) were prepared in ethanol.793 The stoichiometry is 1 1 and the atoms involved in the coordination were two deprotonated oxygens and two nitrogen atoms. v(V—O) (970-985 cm-1) and f4 (1.73-1.83 BM) suggest a monomer however, molecular weights in nitrobenzene suggest a dimer. 

Fig. 2. Polymerization rate and initial monomer concentration a-methylstyrene-iodine-nitrobenzene. . 0.11 KV/cm, o 0 KV/cm. Reproduced, with permission, from Sakurada, Ise, and Tanaka Polymer 8, 625 (1967)...

In the styrene (MJ-indene (Mz) system, rx increased with the field. This result shows that the dissociation of ion pairs at the growing chain ends, the terminal group of which is styrene, was enhanced by the field. As was mentioned above, the field has no effect on the homopolymerization of styrene by boron trifluoride etherate in nitrobenzene (see Fig. 5). This result of the homopolymerization seems to be inconsistent with that obtained for the copolymerization, but can be accounted for as follows. The field-accelerating effect decreases as kp/kp decreases, when an enhancement of the degree of dissociation with the electric field is given. The fact that no field effect was observed on the homopolymerization of styrene with boron trifluoride etherate in nitrobenzene may be attributed to a fairly small value of kp/kp, in addition to the factor af 1. On the other hand, the field enhanced the polymerization of indene by boron trifluoride etherate in nitrobenzene (16). The difference in the field effects of the two monomer systems suggests that the following relation must hold, ... 

These early works have been reviewed by Fioshin (4) and well summarized by Bbeitenbach (5). Besides, Breitenbach has made a study of the polymerization mechanism using the copolymerization method and has shown that the reaction mechanism depends on the ions used in the electrolytic discharge and on the monomer present in the system. Cationic processes were also found to be initiated in a nitrobenzene solution of styrene by the anodic discharge of perchlorate and borotetrafluoride ions. The possibility that the three different mechanisms could occur simultaneously was demonstrated in the same system of acrylonitrile-styrene using a divided electrolytic cell. 

Drijvers and Goethals 52) have reported that excess sulphide functions (monomer and polymer) and diethyl ether have no detectable effect on the dissociation of two sulphonium tetrafluoroborate salts in methylene chloride and nitrobenzene, when present in similar proportions to those in corresponding polymerisation reactions. In contrast to this, however, Jones and Plesch 51) have shown that the dissociation constant of triethyloxonium hexafluorophos-phate in methylene chloride at 0°C increases by a factor of - 2 when small quantities of tetrahydrofuran are added. The latter molecule has a lower dielectric constant than methylene chloride and might therefore be expected to reduce dissociation. These workers have interpreted their results in terms of specific solvation of the cation by ether molecules, with subsequent reduction in the effective charge density of the positive ion and hence in the coulombic force favouring ion pairing, e.g. 

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