Study on the initial stage of emulsion polymerization of vinyl monomers using poly(vinyl alcohol) as a protective colloid – comparison between vinyl acetate (VAc) and methyl methacrylate (MMA)
Comparison of the particle formation mechanism of vinyl acetate (VAc) with that of methyl methacrylate (MMA) in a model emulsion polymerization using poly(vinyl alcohol) (PVA) as a protective colloid was carried out. The concentration of the monomers was 1 ml/100ml-water, which was about 1/100th volume of the monomers compared with ordinary emulsion polymerization. The new particle formation as well as the degree of grafting onto PVA in the VAc system was almost the same as in the MMA system. To realize these results, we calculated for both monomers the reaction times of the initiation of the sulfate radical with monomer (τ1), of the propagation of the polymer radical (τ2), and of the hydrogen abstraction from PVA with the sulfate radical (τ3) and the time of the entry of the sulfate radical into a particle (θ). The times for the MMA system were obtained as τ1=10-5> s, τ2=10-2> s, τ3= 10-8> s, and θ=10-4> s, whereas the times for the VAc system were τ1=10-7> s, τ2=10-3> s, τ3=10-8> s, and θ=10-4> s. The fastest reaction for both system was concluded to be the hydrogen abstraction from PVA, resulting in grafting onto PVA and new particle formation. The grafted polymers coagulated with each other to become a particle. In the case of VAc system, the coagulation of the grafted polymers to result in a particle was calculated to be 4620. In the case of MMA, this was 160 molecules.
KeywordsEmulsion polymerization Initial stage Grafting Vinyl acetate Poly(vinylalcohol) Methyl methacrylate
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