Quantification of spontaneous initiation in radical polymerization of styrene in aqueous miniemulsion at high temperature

Thermal Polymerization of Styrene, Part 2 – (Mini)emulsion Polymerization

“…Independent of the parameter k x there is a slightly different evolution of the molecular weight with conversion for the different bulk models (Figure 3). Especially the significant decrease of the molecular weight using a third order model is in contrast to the almost conversion independent molecular weight found experimentally (Figure 4; compare also to the data of Alam et al11)…”

“…Unexpectedly, the experimental molecular weight of all the experiments conducted in this work is unusually high (partially in the extrapolated region of the GPC‐calibration). Despite the experimental scatter, these high molecular weights could be reproduced, but it is necessary to mention, that the results are in disagreement with the findings of comparable experiments given by Alam et al11 The reason for this discrepancy is unclear at present.…”

“…The standard recipe for the thermal miniemulsion polymerizations of styrene used for all the conducted experiments is following the suggestions of Alam et al11 and Landfester et al13 and consisted of 10 g styrene, 200 g water, 0.45 g hexadecane and 0.075–5 g (varying) SDBS.…”

“…Since the acceleration effect is independent of the presence of monomer droplets (compare to thermal polymerized miniemulsions11) the contribution of droplets with a small specific surface area should not contribute significantly to the radical formation process. It has also been shown by Alam et al that the formation of radicals within the water phase is negligible 11. In the mentioned work an influence of the used surfactant sodium dodecylsulfonate (SDBS) on either the rate or the molecular weight distribution during the bulk polymerization of styrene could also be ruled out.…”

Synthesis of Nanosized (<20 nm) Polymer Particles by Radical Polymerization in Miniemulsion Employing in situ Surfactant Formation

“…[47] The very small particle sizes in the present systems give rise to strong compartmentalization effects, i.e., segregation of propagating radicals, which suppresses bimolecular termination and allows the majority of the propagating radicals to grow until chain transfer to monomer occurs. This type of behavior is normal in emulsionand microemulsion polymerizations with sufficiently small particles, [48][49][50] but has also been observed in welldefined miniemulsion systems with small particles. [35] The smaller the particles, the smaller is the contribution of termination, and consequently a greater fraction of radicals propagate until chain transfer to monomer occurs, thus leading to higher molecular weight.…”