Polymerization vinyl hexanoate

The emulsion polymerization of vinyl hexanoate has been studied to determine the effect of chain transfer on the polymerization kinetics of a water-insoluble monomer. Both unseeded and seeded runs were made. For unseeded polymerizations, the dependence of particle concentration on soap is much higher than Smith-Ewart predictions, indicating multiple particle formation per radical because of chain transfer. Once the particles have formed, the kinetics are much like those of styrene. The lower water solubility of vinyl hexanoate when compared with styrene apparently negates its increased chain transfer, since the monomer radicals cannot diffuse out of the particles. 

A range is given for vinyl hexanoate since the low percentage of monomer used makes determination of the point more difficult. From these observations and the shape of the polymerization curves, it seems that vinyl hexanoate behaves similarly to styrene in showing first-order dependence on monomer concentration during polymerization. 

Kinetics of Vinyl Hexanoate. A series of standard polymerizations was conducted using 10 ml of vinyl hexanoate in a total volume of 140 ml with varying amounts of emulsifier and initiator. The effect of varying initiator, particle number, and organic volume fraction in seeded runs, as well as for unseeded polymerizations, were also studied. The results are summarized in Table II. 

Reimers [102] carried out batch copolymerizations in both macro- and equivalent miniemulsions. MMA was used as the main monomer. The MMA was copolymerized in macroemulsion- or miniemulsion with p-methylstyrene (pMS), vinyl hexanoate (VH), vinyl 2-ethylhexanoate (VEH), vinyl n-decanoate (VD) or vinyl stearate (VS). The comonomers were copolymerized at 10%wt comonomer, 90%wt MMA. SLS was used as the surfactant and KPS as the initiator. The comonomers (all highly water insoluble) were used as the costabilizer. Miniemulsions were sonicated, while equivalent macroemulsions were only subjected to vigorous mixing. Polymerizations were carried out at 60 °C. 

As the water solubility of the comonomer decreases, the difference in incorporation of the hydrophobic monomer between the mini- and macroemulsion polymerization becomes more pronounced. This was seen in the copolymerization of VH/MMA. The fraction of the hexanoate in the copolymer formed in the miniemulsion polymerization was substantially higher than that found with the macroemulsion. This incorporation closely follows the copolymer equation. The VEH/MMA miniemulsion copolymerization also followed the copolymer equation. Differences between the mini- and macroemulsion polymerization are not as pronounced in this system. For the VD/MMA and VS/MMA systems there were large differences between the two copolymerizations. In addition, none of the mini- or macroemulsion copolymerizations of vinyl decanoate or vinyl stearate are predicted by the copolymer equation. The miniemulsion copolymerizations fall above the prediction curve (more hydrophobic monomer incorporation than predicted), and the macroemulsions fall below. In these cases, both micellar and droplet nucleation took place in the miniemulsion polymerizations, and the presence of micelles tended to enrich the concentration of the hydrophobic monomer in the droplets, since the micelles would likely be richer in the more water-soluble MMA. 

Bataille and Shariffi-Sanjani [34] reported the synthesis of a copolymer of 2-ethylhexyl acrylate and vinyl 2-ethyl hexanoate by solution polymerization using benzene as a solvent and benzoyl peroxide as an initiator at 65°C. The viscosity index improvement property of the purified copolymer was checked in two ISO 20 base oils. The polydispersity of the copolymers was observed to influence greatly the viscosity index improvement property. 

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