P-Dioxene

Similar dehydrofluorination occurs with polyfluorinated heterocycles. 2,2-Bis(trifluoromethyl)-3,4-difluorooxetane gives 3-fluoro-4,4-bis(trifluoromethyl)-2-oxete [19] (equation 17), and heptafluoro-p-dioxane yields hexafluoro-p dioxene [20] (equation 18)... 

CPT-SO > System. Bulk copolymerization of CPT and SO> takes takes place spontaneously at a remarkable rate even at —15 °C. In comparison with the thermal initiation of p-dioxene and maleic anhydride which proceeds through a similar charge transfer complex at room temperature (13), the interaction between CPT and S02 seems more pronounced, giving the propagating species at a lower temperature. 

The photooxidation or 2,3-diphenyl-p-dioxene was used to define the quantum yield of singlet oxygen fornation. 

Figure 4. Photooxidation of 2,3-diphenyl-p-dioxene with P-RB (Photooxidation with P-RB-1520 was carried out in 50% MeOH and 50% CH2CI2 Solution)...

Diphenyl-p-dioxene was prepared according to the method of Summerbell and Berger, and the solid thus obtained was recrysta-lized twice from ethanol, m.p. 93-94°C (uncorrected)32. 

Iwatsuki and Yamashita (46, 48, 50, 52) have provided evidence for the participation of a charge transfer complex in the formation of alternating copolymers from the free radical copolymerization of p-dioxene or vinyl ethers with maleic anhydride. Terpolymerization of the monomer pairs which form alternating copolymers with a third monomer which had little interaction with either monomer of the pair, indicated that the polymerization was actually a copolymerization of the third monomer with the complex (45, 47, 51, 52). Similarly, copolymerization kinetics have been found to be applicable to the free radical polymerization of ternary mixtures of sulfur dioxide, an electron donor monomer, and an electron acceptor monomer (25, 44, 61, 88), as well as sulfur dioxide and two electron donor monomers (42, 80). 

Similar results have been noted in terpolymerizations involving the p-dioxene-maleic anhydride (49, 51, 52) and vinyl ether-maleic anhydride (45, 49) and vinyl ether-fumaronitrile (49) monomer pairs. Iwatsuki and Yamashita (46) concluded that the molecular complex formed between p-dioxene and maleic anhydride is attacked on the p-dioxene side by a radical to yield the maleic anhydride radical which is considered to be the main growing radical. Thus, a monoradical propagation step is considered operative. 

The interactions of a-olefins or styrene with sulfur dioxide (16) or a-olefins (24, 58, 78), frans-stilbene (64), styrene (1,63), p-dioxene (52), 2,2-dimethyl-l,3-dioxole (17), or alkyl vinyl ethers (1, 63) with maleic anhydride yield charge transfer complexes which are stable and generally readily detectable either visually or by their ultraviolet absorption spectra. However, under the influence of a sufficiently energetic attack in the form of heat or free radicals, the diradical complexes open, and alternating copolymers are formed. 

As additional support for the diradical mechanism, it was shown that the 3,4-diethoxy-l,2-dioxetane (8) and the p-dioxene-l,2-dioxetane had identical activation energies, implying that the C-C bond is not significantly stretched in the activated complex. That these notions on substituent effects in dioxetane decomposition are grossly oversimplified has come clearly into focus in recent years (Table 4). The fact that little yet is understood about the correspondence between activation parameters and dioxetane structure has already been amply expounded in Section V.l.B. Nevertheless, a few additional comments seem appropriate on this subject in... 

Chlorine is virtually absent in the copolymer produced in the azobisisobutyronitrile (AIBN) catalyzed copolymerization of styrene and maleic anhydride in the presence of chloroform or carbon tetrachloride (3, 4), or of p-dioxene and maleic anhydride in the presence of acrylonitrile in chloroform (5). This absence indicates that trichloromethyl radicals generated by the reaction of the chlorinated hydrocarbons with the radicals from AIBN are not incorporated into the polymer chain. Similarly, there is little or no cnlorine in the alternating copolymer that is formed in the copolymerization of styrene and methyl methacrylate in the presence of ethylaluminum sesquichloride (EASC) in the presence of chloroform and carbon tetrachloride, and with or without a peroxide initiator (6). 

Coe, P.L. Dodman, R Tatlow, J.C. Highly fluorinated heterocycles. XL Rreparation of some polyfluoro-p-dioxenes. Reactions of hexafluoro-p-dioxene. J. Fluorine Chem. 1975, 6(2), 115-128. 

The rate of 2,3-diphenyl-p-dioxene photooxidation using RB dissolved in MeOH as the sensitizer essentially does not change as a function of the rate of flow of oxygen. The rate of... 

Figure 22-9, Absorptivity, A CT, of the charge transfer complex from p-dioxene, PD, and maleic anhydride, MAH, as a function of the volume fraction, 0m ah maleic anhydride in chloroform Initial concentrations 0.5045 (mol PD)/liter and 0.5082(mol MAH)/liter. (After S. Iwatsukiand Y. Yamashita.)...

On the other hand, the joint polymerization of a series of electron-accepting and electron-donating monomers leads to alternating copolymers, mostly as a mixture with the head-to-head cycloaddition products. Electron-accepting maleic anhydride, fumaric ester, sulfur dioxide, or carbon dioxide in combination with electron-donating butadiene, isobutylene, vinyl ether, and p-dioxene or vinyl acetate belong to this series. 

Both the polymerization rate and the composition of the copolymer also depend on the solvent. Solvents can determine the position of the complex equilibrium (see also Table 22-7). Thus, for example, the homopolymerization of a CT complex can be converted into a copolymerization of the CT complex with one of its two monomers, or even convert to a terpolymerization with both of its monomers when the solvent is changed. Such effects may, for example, be responsible besides the dilution effect for the variation in the acrylonitrile content of the terpolymer produced by the joint polymerization of acrylonitrile/p-dioxene/maleic anhydride when the kind and concentration of solvent used are changed (see Figure 22-10). 

Figure 22-10. Dependence of the acrylonitrile content of the terpolymer produced in the terpolymerization of p-dioxene, maleic anhydride, and acrylonitrile in different solvents. (After data from S. Iwatsuki and Y. Yamashita.)...

The nature and the amount of solvent can influence the yield and the composition of the copolymers in these copolymerizations. Thus, copolymerization of phenanthrene with maleic anhydride in benzene yields a 1 2 adduct. In dioxane, however, a 1 1 adduct is obtained. In dimethyl formamide, no copolymer forms at all [193]. Another example is a terpolymerization of acrylonitrile with 2-chloroethyl vinyl ether and maleic anhydride or with p-dioxene-maleic anhydride. The amount of acrylonitrile in the terpolymer increases with an increase in the 7t-electron density of the solvent in the following order [194] ... 

Since the 1940s, it has been recognized that MA forms alternating copolymers with various olefinic monomers such as styrene,allyl acetate,and p-dioxene. Recently, dienes, furan /V-vinyl compounds,and unsaturated sulfides have also been added to this list. 

Both alkyl and aryl vinyl ethers and a variety of unsaturated cyclic ethers will undergo free-radical copolymerization with MA, under mild conditions, to give equimolar copolymers. DuPlessis and coworkers have shown that dialkyl maleates and alkyl vinyl ethers will also undergo equimolar copolymerization. This occurs even though all of the monomers are very sluggish to free-radical homopolymerization. In some cases, spontaneous or thermal copolymerization can even occur between vinyl ethers and MA, such as 1,2-dimethoxyethylene, " p-dioxene, and conjugated dihydro-anisole. It is also known that vinyl ethers will polymerize in the presence of amide-MA mixtures, with the amide-MA CTC playing the role of initiator. ... 

Several different types of unsaturated cyclic ethers, such as p-dioxene, 2,3-dihydropyran, furan, 2-methylfuran, 2,3-dihydrofuran, 2,2-dimethyl-l,3-dioxole, 2-methylene-oxetane, and benzofuran have been copolymerized with MA. Only the 2-methylene-oxetane fails to copolymerize in a 1 1 fashion with MA. 

The alternating copolymerization of p-dioxene with MA has received substantial study.Similar to other vinyl ethers, p-dioxene is not amenable to free-radical-initiated homopolymerization. However, polymerization of the yellow-colored solution of the two monomers occurs readily with or without a free-radical initiator. Copolymerization is inhibited by standard free-radical inhibitors, such as hydroquinone. Copolymerizations of monomer mixtures have been examined both neat and in a variety of solvents, using AIBN at 60°C. As expected, the rate of copolymerization and the reduced viscosity of the copolymer depends on the monomer feed ratio and have their maximum at a 1 1 monomer mixture. In addition, alternating copolymers were obtained regardless of the monomer mixture ratio. 

Studies show that the p-dioxene-MA copolymerization rate is considerably lower than that of 1,2-dimethoxyethylene-MA, i.e., less than 6- A comparison of the various copolymerization rates showed c/5-1,2-dimethoxyethylene > /rflAZ5-l,2-dimethoxyethylene > p-dioxene.Steric effects are advanced to account for the apparent sixfold lower reactivity of... 

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