Monomer-benzene solutions

Photoinitiation of polymerization of MMA and styrene by Mn(facac)3 was also investigated, and it was shown that the mechanism of photoinitiation is different [33] from that of Mn(acac)3 and is subject to the marked solvent effect, being less efficient in benzene than in ethyl acetate solutions. The mechanism shown in Schemes (15) and (16) illustrate the photodecomposition scheme of Mn(facac)3 in monomer-ethyl acetate and monomer-benzene solutions, respectively. (C = manganese chelate complex.)... 

Another case in which bonds were made where none existed previously is that of irradiation of AsClj in benzene solution (76) which led to formation of PhAsCl2 and PhjAsCl, and even PhjAs. Yet another example 51) is the formation of FeCpj by irradiation of Fe(CO)j in cyclopentadiene (monomer) solution. While these examples may not tell us when the reaction does occur, they do show that initial bonding is not indispensable. 

Solvent Effects in the Sn Spectra of Poly(TBTM/MMA). Samples of poly(MMA/TBTM) synthesized by the free-radical copolymerization of the appropriate monomers were solutions in benzene with approximately 33% solids (weight to volume). The particular formulation chosen as representative of the class contained a 1 1 ratio of pendant methyl to tri-n-butyltin groups. In preparing the dry polymer, the benzene was removed in vacuo with nominally 5% by weight residual solvent. 

Radical chain polymerizations are characterized by the presence of an autoacceleration in the polymerization rate as the reaction proceeds [North, 1974], One would normally expect a reaction rate to fall with time (i.e., the extent of conversion), since the monomer and initiator concentrations decrease with time. However, the exact opposite behavior is observed in many polymerizations—the reaction rate increases with conversion. A typical example is shown in Fig. 3-15 for the polymerization of methyl methacrylate in benzene solution [Schulz and Haborth, 1948]. The plot for the 10% methyl methacrylate solution shows the behavior that would generally be expected. The plot for neat (pure) monomer shows a dramatic autoacceleration in the polymerization rate. Such behavior is referred to as the gel effect. (The term gel as used here is different from its usage in Sec. 2-10 it does not refer to the formation of a crosslinked polymer.) The terms Trommsdorff effect and Norrish-Smith effect are also used in recognition of the early workers in the field. Similar behavior has been observed for a variety of monomers, including styrene, vinyl acetate, and methyl methacrylate [Balke and Hamielec, 1973 Cardenas and O Driscoll, 1976, 1977 Small, 1975 Turner, 1977 Yamamoto and Sugimoto, 1979]. It turns out that the gel effect is the normal ... 

Benzothiophene-1,1-dioxide (VI) in benzene solution, is converted in sunlight into a stable photodimer (Vila or VHb), which is considered to contain a central cyclobutane structure.56 196 Even though the monomer cannot be isolated on thermal decomposition of the dimer, the latter in boiling ethyl phthalate decomposes, forming sulfur dioxide and... 

The complexes MLa (M = Th, U) with HL = oc-, /J- or y-isopropyl tropolone are also known. Molecular weight determinations (benzene solution) for the thorium compounds indicate that the a compound is close to a dimer, whereas the 0 and y derivatives are approximately trimeric. The corresponding uranium(IV) complexes are all monomers. All three thorium compounds readily form monohydrates and the structure of the hydrated y-isopropyltropolonate is described on p. 1144. 

The four compounds with R = H are isostructural, and in the thorium complex the eight-coordinate metal atom lies at the centre of a distorted square antiprismatic array of four N and four O atoms. In benzene solution, however, the molecular weights of the complexes with R = H indicate that they are dimers, whereas those with R = Me are monomers.166... 

The polymerization vessel is illustrated in Pig. 8. Ampoules A and B contained dilute and concentrated benzene solutions of the seed polymer, respectively, and ampoules C and D contained tetrahydrofuran (or dimethoxyethane) and a benzene solution of the monomer. The polymerization vessel was connected to a high-vacuum line, evacuated, flamed and sealed off. Then the break-seal on ampoule B was crashed, and the whole vessel was washed with the concentrated solution of living polymer. All the solutions were brought to E and the vessel was washed by condensing the benzene using a pad at Dry Ice-methanol temperature. The solvent was distilled into F from E and E was sealed off. The seals on A, C, and D were broken, and the dilute solution of living polymer was collected into G by turning the whole vessel upside down,... 

The structure of a /t-iodo dimer, [ Con(cobyrinic acid hexamethyl ester) 2lll has been determined.253 The cobalt atoms are displaced from the N4 plane by 0.11 A and 0.13 A respectively, and the Co—I—Co group is slightly bent. The dimer is diamagnetic due to strong antiferromagnetic coupling between the two Co atoms. It exists in equilibrium with the monomer in benzene solution. 

The thermal decay process of the radicals is a bimolecular reaction. The decay rate increases with increasing temperature. At 100° C, a half-life of 12 minutes has been observed for methyl methacrylate popcorn radicals. A fast decay rate takes place when the dry popcorn is swollen in a liquid such as benzene. That means that during the proliferous growth process, when the polymer is swollen by the monomer, a decay process also occurs, and a stationary radical concentration in the growing polymer popcorn results. A liquid that does not swell the polymer (for example, methanol for polystyrene) does not influence the decay rate. A much higher rate of radical decay is obtained with a benzene solution of diphenylpicrylhydrazil. The reaction rate between the polymer radical and inhibitor radical may be measured. 

Systems containing monomer and DMF but no other diluent were discussed in the previous section, and it was noted that a maximum rate is associated with intermediate monomer-DMF compositions. Imoto (79) observed a similar effect with monomer-benzene-DMF mixtures. A shallow minimum in polymerization rate was found at a low benzene level and then a very pronounced maximum at a higher benzene content. Molecular weight increased monotonically, however, with the benzene/ DMF ratio. In these ternary systems the amount of DMF was not enough to keep the polymer in solution but considerable swelling must have occurred. Thomas, Thomas and Deichert (130) show electron photomicrographs of polymer made under these conditions. 

As shown by the gel permeation chromatograph in Figure 6, the average molecular weight of poly(styrene-co-maleic anhydride) obtained by adding the macroradical to a benzene solution of the monomers was over 250,000. No copolymer was obtained under comparable conditions in the absence of the macroradicals. Attempts to use these macroradicals to produce copolymers in an acetone solution were unsuccessful. 

Methylene trimethylarsorane is a monomer in benzene solution. Study of its H and 13C NMR spectra led to some unexpected conclusions, distinctly different from the findings with the phosphorus analog (80). As shown in Table III, the 5 and J characteristics of the CH2 nuclei are not nearly as different from those of the CH3 groups as are those of CH2 and CH3 in the phosphorus ylide (58). Whereas /(H2C) = 149 of the latter indicates an sp2 carbon (the value for ethylene is 150 Hz), J(H2C) = 131 in the former rather points to an sp3 carbon for the carbanion in (CH3)3-AsCH2. (Methane, 125 Hz CH3 in the ylide, 133 Hz )... 

At room temperature, pentamethylarsorane is a colorless liquid of a characteristic odor which resembles the analogous antimony compound. It crystallizes below — 6°C and can be sublimed under reduced pressure at — 10°C. The (CH3)5As is a monomer in benzene solution and shows a molecular ion in the mass spectrum with very low intensity. The vibrational spectra, infrared and Raman, could be assigned to a trigonal-bipyramidal skeleton. There are striking similarities to the spectra of Sb(CH3)6 (IS). 

Polymerization and copolymerization of the acryloyl or methacryloyl type monomers having 5-FU or theophylline were performed in methanol or benzene solution at 23 °C or 60 °C using AIBN as an initiator. The results of the polymerization are shown in Tables 6 and 7. The homopolymers of AFU,... 

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