Ở nhiệt độ cao phản ứng khác xảy ra, mà làm cho cấu trúc của mạng lưới vô cùng phức tạp. Thật vậy, hydroxyls thứ cấp được hình thành khi ringopening của epoxit có thể biến phản ứng với oxiranes Tiền thân của: | 308 CHAIN POLYMERIZATIONS one. The increase in volume dV dt that results drives the surfactant of the empty micelles toward the external envelope of the particles micelles thus disappear from the medium by becoming particles or by supplying surfactant molecules to the already formed particles. As soon as all the micelles have been used up by one of the mechanisms mentioned above first period in Figure corresponding to approximately 15 monomer conversion the number of particles Np can be considered constant until the end of the polymerization. The rate of polymerization during this second period in Figure can be expressed by the relation Rp kp Mpart N Thus it will be constant up to 70-80 conversion. Assuming that free radicals are generated at constant rate d RM dt p const and that all of them serve to create particles at the time ti corresponding to the total disappearance of micelles Np can be written as Np pti At t1 a particle created at t0 will exhibit the volume V ti t0 B ti - t0 with its volume at t0 when it was a micelle being negligible. The surface of its external envelope can be easily deduced from its volume a ti t0 36n 1 3 p. ti - t0 2 3 Figure . Kinetics of the monomer conversion for an emulsion polymerization in a closed batch reactor. Because the number of particles generated for the period of time dt is pdt the total external surface at time t1 can be written ti Ati a ti t0 pdt 36n 1 2 3t1 0 ANIONIC POLYMERIZATION 309 Because this total surface can be directly related to the concentration S of the surfactant and to its molar surface as All as S one obtains the following for the expression of Np Np as S 0 6 The Smith-Ewart model describes satisfactorily the polymerization of styrene isoprene and methyl methacrylate for these systems it can be used to predict the size of the latex particles and the corresponding molar masses. In contrast it is unsuited for the case of monomers partially water-soluble or polymers insoluble in .
