Vazo®

Vazo-52, Self-Reactive Solid Type D, Temperature Controlled (2,2Gazodi(2,4-dimethylvaleronitrile)). 

A container was charged with a solution of Vazo 52 catalyst and 2,2 -azobis(2,4-dimethyl pentane nitrile) (4.5 g) dissolved in acetone (600 g) a second container was charged with methyl methacrylate (540 g) and 2-hydroxy ethyl methacrylate (180 g). The first and second containers were uniformly fed into a reactor for 330 and 240 minutes, respectively, and then refluxed for 1 hour. After standard workup the product was isolated in 100% yield, having aMn of 30,308 daltons, Mw of93,195 daltons, and a PDI of 3.07. 

The 80/20 (wt/wt) methyl methacrylate (MMA) n-butyl acrylate (BA) macromonomer was prepared in the following manner. To a 3000-mL flask 440.1 g MMA, 200.0 g BA, and 150.0 g methyl ethyl ketone (MEK) were added. The mixture was stirred and heated to reflux under a nitrogen blanket. After a 10-min hold, 30.0 g MEK, 0.140 g Vazo-67, and 0.050 g Co(dimethylglyoxime-BF2)2 were added to the flask. After a 5-min hold, 359.9 g MMA, 200.0 g MEK, and 1.90 g Vazo-67 were added over a 3.5-h period. The mixture was held 1 h at reflux after the feed. Subsequently, 150.0 g MEK and 1.00 g Vazo-52 were feed over an hour. The mixture was held for 1 h at reflux. The mixture was then allowed to cool to room temperature. A more detailed procedure and the Co(dimethylglyoxime-BF2)2 synthesis are given in reference 18. 

The methyl methacrylate-itaconic acid copolymer, P(MMA-co-ItaA), was prepared by slow free-radical solution polymerization in methanol under nitrogen using 2,2 -azobis-(2,4-dimethyl valeronitrile)(du Pont Vazo 52) as initiator. The molar ratio of monomer to initiator was in the range of 5xl03 to 10xl03. Reaction at 50°C for 30 to 40 hrs gave conversions of 10 to 30%. The reaction mixture was added to cold, deionized water and the precipitated polymer obtained was rinsed with 2-propanol. 

The following discussion illustrates the prepolymerization solution composition of a MHAP and the hypothetical results this composition could have on polymer architecture. Typical concentrations are 0.035 M SDS, 0.049 M C12EO5, 0.011 M LMA, 67 ppm by wt Vazo 52 initiator, and 1.4 M AAm. Solely for purpose of illustration, assume 25 LMA molecules in a micelle. (This number is reasonable within a factor of 2 or 3.) Assume that the SDS critical micelle concentration (CMC) for the mixed micelle is approximately that of C12EO5 (reasonable from the results of refs. 29 and 30) and assume that all of the Vazo 52 molecules are in the micelle. It is then calculated that the micelle consists of the 25 LMA molecules, 80 SDS molecules, 112 C12EO5 molecules, and 0.6 initiator molecules. Assuming complete polymerization, a 5 X 10 molecular weight (MW) molecule would then consist of 22 blocks of 25 LMA monomers each and 3100 AAm monomers between each block of LMA. 

The effect of initiator concentration in the model system is shown in Table I. Amounts of Vazo 52 from 67 to 335 ppm by wt produce practically an invariant PLMA MW, although there might be a slight maximum at 134 ppm (1 sigma error is 300). This result is contrary to the usual case where an increase in initiator concentration causes a decrease in MW. This relative insensitivity to initiator concentration is consistent with the micellar solution polymerization model already described because molecules in a micelle are in their own microenvironment. A concentration of 200 ppm of initiator is always used for polymerization in the model system because this concentration usually gives at least one initiator molecule per micelle. These results prove that initiator concentration is not a factor in these experiments. 

Write down the mechanism for the free-radical polymerization of vinylacetate initiated by 2,2 -azobis(2,4-dimethylpentanenitrile) (Vazo 52) in ethyl acetate including (a) initiation, (b) propagation, and (c) termination by disproportionation. 

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