Polymerization peroxide-initiated

Fig. 10.—Benzoyl peroxide-initiated polymerization of vinyl-i-j3-phenyl-butyrate in dioxane at 60°C plotted as a first-order reaction. [M]o and [M ] represent concentrations of monomer initially and at time t, respectively. In experiments 1, 2, and 3, respectively, [M]o = 2.4, 7.28, and 5.97 g. of monomer per 100 cc. of dioxane. (Results of Marvel, Dec, and Cooke obtained po-larimetrically.)...

Solomon (3, h, 5.) reported that various clays inhibited or retarded free radical reactions such as thermal and peroxide-initiated polymerization of methyl methacrylate and styrene, peroxide-initiated styrene-unsaturated polyester copolymerization, as well as sulfur vulcanization of styrene-butadiene copolymer rubber. The proposed mechanism for inhibition involved deactivation of free radicals by a one-electron transfer to octahedral aluminum sites on the clay, resulting in a conversion of the free radical, i.e. catalyst radical or chain radical, to a cation which is inactive in these radical initiated and/or propagated reactions. 

The rate expression Eq. 3-32 requires a first-order dependence of the polymerization rate on the monomer concentration and is observed for many polymerizations [Kamachi et al., 1978], Figure 3-2 shows the first-order relationship for the polymerization of methyl methacrylate [Sugimura and Minoura, 1966], However, there are many polymerizations where Rp shows a higher than first-order dependence on [M], Thus the rate of polymerization depends on the -power of the monomer concentration in the polymerization of styrene in chlorobenzene solution at 120°C initiated by t-butyl peresters [Misra and Mathiu, 1967]. The benzoyl peroxide initiated polymerization of styrene in toluene at 80°C shows an increasing order of dependence of Rp on [M] as [M] decreases [Horikx and Hermans, 1953], The dependence is 1.18-order at [M] = 1.8 and increases to 1.36-order at [M] = 0.4. These effects may be caused by a dependence of the initiation rate on the monomer concentration. Equation 3-28 was derived on the assumption that Rt is independent of [M], The initiation rate can be monomer-dependent in several ways. The initiator efficiency / may vary directly with the monomer concentration... 

The initiation process appears more complicated than described above, although data are not available in more than a few systems. The benzoyl peroxide initiated polymerization of styrene involves considerable substitution of initiator radicals on the benzene ring for polymerizations carried out at high conversions and high initiator concentrations. About one-third of the initiator radicals from t-butyl peroxide abstract hydrogen atoms from the a-methyl groups of methyl methacrylate, while there is no such abstraction for initiator radicals from benzoyl peroxide or AIBN. 

Fig. 3-10 Inhibition of the benzoyl peroxide-initiated polymerization of vinyl acetate by duroquinone at 45°C. The three lines are for different concentrations of duroquinone. After Bartlett and Kwart [1950] (by permission of American Chemical Society, Washington, DC).

Fig. 3-15 Autoacceleration in benzoyl peroxide-initiated polymerization of methyl methacrylate in benzene at 50°C. The different plots represent various concentrations of monomer in solvent. After Schulz and Haborth [1948] (by permission of Huthig and Wepf Verlag, Basel).

The benzoyl peroxide-initiated polymerization of a monomer follows the simplest kinetic scheme, that is, Rp = kp A (fkd /k,)1 2 with all rate constants and / being independent of conversion. For a polymerization system with [M]0 = 2M and [I]0 = 10-2 M, the limiting conversion px, is 10%. To increase pYj to 20% ... 

Since aliphatic azo compounds can, at best, act only as hydrogen abstracters in oxidation reactions, the color formation associated with oxygen addition (it is due to fragments from peroxide-initiated polymerization) is eliminated or reduced even in the presence of atmospheric oxygen. 

Conix, A., and G. Smets Benzoyl peroxide initiated polymerization kinetics of vinyl monomers in various solvents. J. Polymer. Sci. 10, 525 (1953). 

Poly (benzyl ether) [G-2]-TEMPO, [G-3]-TEMPO, and [G-4]-TEMPO compounds have been synthesized and used as additives in the benzoyl peroxide initiated polymerization of styrene [127] (see Scheme 15c). After an induction period, chain growth is observed. However, the MWD is larger than in a dendrim-er-free TEMPO modulated system (Mw/Mn 2). The expectation that the den-drimer would isolate the growing chain end and prevent side reactions is not borne out. Polymerizations of methylmethacrylate, vinylacetate, and n-buty-lacrylate with the same initiator/TEMPO recipe are disappointing. 

One half of an aqueous solution of vinylpyrrolidone (VP) is added to the reactor while the other half is added in portions during the polymerization. The polymerization is initiated when hydrogen peroxide and ammonia are added to the reaction mixture. The ammonia serves as a buffer in the solution in order to provide an alkaline condition, thus preventing the splitting off of the acetaldehyde from the monomer during the reaction. The rate of the peroxide-initiated polymerization is expressed as ... 

Vinyl chloride is polymerized primarily by peroxide-initiated polymerization in aqueous suspension,... 

If it is assumed that / is constant for a given series, a plot of (1/DF) vs. (k U]/ Rp) should have a slope of / and an intercept of k r/kp at (ka[I]/Rp) = 0. The benzoyl peroxide-initiated polymerization data were analyzed in this manner. There was considerable experimental scatter in these plots and therefore, the data are given (Table VII) as the least squares slopes and intercepts as well as their 95% confidence limits. The average values of k r/kp, ranging from 0.8 to 1.1 X... 

The other parameters for the benzoyl peroxide-initiated polymerizations were calculated in the following manner. Using the subscripts B and P to denote the benzoyl peroxide- and persulfate-initiated polymerizations respectively. Equations 2 and 3 give... 

Thus values of az can be calculated for the benzoyl peroxide-initiated polymerizations from the known values of az (persulfate-initiated polymerizations), and the ratios of average particle volumes and polymerization rates. These values of az may then be substituted in Equations 3 and 4 to give values for f/k and fk which may then be combined to give values for f and The results of these calculations are shown (Table VIII-A). The values of az are all considerably less than 2. From Figure 13 for the case where the radicals are generated in, or enter,... 

Thermally-activated peroxide initiated polymerizations were performed in the normal scanning temperature mode (+20° min"J, 40 mm min I chart speed) with the unmodified DSC-2 apparatus. The scan baseline was obtained by a second scan of the reacted material. Temperature range 30O-250°C. The curve area integrations... 

Peroxide initiated polymerizations (scan 30°-250°C) of lauryl acrylate (LA), I,6-hexanediol diacrylate (HDDA), neopentyl glycol diacrylate (NPGDA), and trimethylol propane triacrylate (TMPTA) revealed total polymerization heats per mole of C=C of 19.2, 17.6, 16,7, and 15.4 kcal, respectively. PhotoactIvated Trigonal 14 initiated polymerizations at 40° yielded total polymerization heats per mole of C=C of 17.4, 11.7, 8.2, and 9.1 kcal for LA, HDDA, NPGDA, and TMPTA, respectively. At 60°C the photopolymerization heats for the latter three monomers increased to 16.6, 9.7, and 10.2 kcal per mole of C=C, respectively. 

The computer program simulates the batch polymerization of styrene and has been applied to the relatively low temperature peroxide-initiated polymerization typical of suspension processes and to higher temperature bulk, thermal conditions. It has been useful in the design of new suspension processes and for more general process analysis. 

Thus, since Ep is less than 1(4 +Et), a typical value being —45kJ/mol, the chain length will decrease with temperature for thermally initiated polymerization. In contrast, if photochemical initiation is used, for which E 0, then Ey is positive (a typical value being 20kJ/mol) and the molar mass will then increase with increasing temperature. For the redox-catalysed, peroxide-initiated polymerization discussed above, Ey will be close to zero, so the chain length will not be sensitive to temperature. 

Problem 6.17 In a benzoyl peroxide initiated polymerization of styrene it is desired to double the initial steady rate of polymerization without changing the initial number-average degree of polymerization. How could this be achieved by changing only the monomer and initiator concentrations ... 

A rapid copolymerization of diallyl adipate with an unsaturated polyester using a small quantity of lauryl mercaptan and stannous chloride along with dibenzoyl peroxide has been described. This patented procedure is of particular interest in the manufacture of flexible coatings or textiles. Procedure 9-2 may be investigated as a general method of accelerating conventional peroxide-initiated polymerizations provided the patent does not impose restrictions on such work. 

Example 2.2 Unsaturated polyester resins, which are used as the matrix component of glass-fiber composites, may be obtained by the copolymerization of maleic anhydride and diethylene glycol. The low-molecular-weight product is soluble in styrene. Describe, with the aid of equations, the possible structures of the prepolymer and that of the polymer resulting from benzoyl peroxide-initiated polymerization of a solution of the prepolymer in styrene. 

In a benzoyl peroxide initiated polymerization of 2 moles of styrene in benzene at 85 °C ( d = 8.94 X 10 L/mole-s at 85 °C). How much benzoyl peroxide will be required in the polymerization solution to attain an average molecular weight of250,000 Assume that termination occurs only by recombination and no chain transferring takes place. 

The reactivity of the initiating radicals toward the backbones can vary and this can also change the efficiency of grafting. Benzoyl peroxide initiated polymerizations of methyl methacrylate monomer, for instance, in the presence of polystyrene yield appreciable quantities of graft copolymers. Very little graft copolymers, however, form when di-r-butyl peroxide initiates the same reactions. Azobisisobutyronitrile also fails to yield appreciable quantities of graft copolymers. This is due to very inefficient chain transferring to the polymer backbones by r-butoxy and isobutyronitrile radicals. 

Methyl ethyl ketone peroxide initiator, polymerization vinyls t-Butyl peroxyisopropyl carbonate initiator, polymerizations Propionyl peroxide initiator, polymers... 

FIGURE 7.2 An illustration of the grafting-from technique (a) created radicals immediately react with the monomer and (b) radicals react with air and the created peroxides initiate polymerization of the monomer. 

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