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Radical polymerization in homogenized butyl acrylate emulsion
Author(s) -
Juraničová Viera,
Capek Ignác
Publication year - 2002
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/1521-3900(200203)179:1<275::aid-masy275>3.0.co;2-c
Subject(s) - emulsion polymerization , polymerization , monomer , polymer chemistry , emulsion , butyl acrylate , chemistry , aqueous solution , bulk polymerization , acrylate , peroxide , radical polymerization , polymer , organic chemistry
The addition of a small amount of monomer strongly decreased the clouding temperature of nonionic emulsifier (Tween 20). The clouding temperature of the Tween 20 aqueous solution was independent of emulsifier concentration but it strongly varied in the presence of monomer. The decreased cloud temperature was attributed to the penetration of monomer molecules into the interfacial layer that increased the flocculation of microdroplets (monomer‐swollen micelles). The surface tension of homogenized ((mini)emulsion) butyl acrylate aqueous emulsion was much smaller than that estimated at or above CMC of Tween 20. The polymerization rate vs. conversion curve of the (mini)emulsion deviates from the three rate intervals typical for the emulsion polymerisation. The shape of the rate‐conversion curve reminds more the four rate intervals curve. Interval 2 is overlapped with the initial maximal rate and rate shoulder at higher conversion. The initial maximal polymerization rate (R p,max,1 ) is attributed to the abrupt increase in polymer particles, the polymerization under monomer saturated condition and emulsifier containing peroxide groups (Tw peroxid 20). The rate of emulsion polymerization of BA initiated by ammonium peroxodisulphate (APS) is ca. by one order of magnitude larger than that of blank polymerization (without APS). The second maximal rate (rate shoulder) can result from the gel effect. The more pronounced increase in R p,max,1 with Tw 20 concentration supports the presence of peroxide groups. The slight dependence of R p,max,2 on [Tw 20] for both APS and DBP (dibenzoyl peroxide) is discussed in terms of the depressed radical entry rate into the close packed surface later of polymer particles. The low activation energy is attributed to the decreased barrier for entering radicals into the polymer particles with increasing temperature. This is more pronounced with the accumulation of covalently bound emulsifier moieties (resulting from Tw peroxid 20) at the particle surface. The ratio of the final number of polymer particles to the initial number of monomer droplets (N p /N drop ) promotes the partial monomer droplet nucleation. The dye approach indicates that the degree of depletion of monomer droplets decreases from the classical emulsion polymerization to the polymerization in pre‐homogenized emulsions and the emulsion polymerization with a prolonged‐emulsification interval.