Add time:08/20/2019         Source:sciencedirect.com

Emulsion copolymerizations of chlorotrifluoroethylene (CTFE) vinyl acetate (VAc) and vinyl propionate (VPr) under redox initiation conditions were investigated. Reactivity ratios (r) determined for VAc and CTFE in the VAc/CTFE system were 0.68 ± 0.11 and 0.04 ± 0.02, respectively. The reactivity ratios for VPr and CTFE in the VPr/CTFE system were 0.63 ± 0.04 and 0.08 ± 0.01, respectively. Vinyl ester-centred triad distributions of the copolymers were measured by 1H nuclear magnetic resonance spectroscopy and were used to calculate conditional probabilities for monomer placements. These values were compared to conditional probabilities calculated from reactivity ratios, conversions and monomer feed compositions. Significant differences between the experimental and calculated conditional probabilities were observed. The variations in the conditional probabilities could be attributed to the dissimilar comonomer solubilities, which results in a different monomer concentration at the site of polymerization than is expected based on the amounts added to the reactor. This work cites the danger of using emulsion polymerization to obtain r values for monomer pairs. By using sequence distribution information, the concentration of monomers at the site of polymerization can be calculated, which is useful for investigating the location of polymerization.

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