Inisurfs Structures

Beside the synthesis of new inisurf structures, a second topic was the search for possibilities to increase their efficiency in heterophase polymerizations. In order to achieve that goal, methoxyoligo(ethylenye oxide-Z)/ocA -butylene... 

In common with conventional surfactants, Inisurfs and Transurfs, Surfmers form micelles in aqueous solutions above the CMC. The organized monomer aggregates of colloidal dimension are microscopically heterogeneous and may affect polymerization kinetics and polymer structure and properties. 

Problems exist with the chemical and structural purity of the inisurfs especially from the colloidal point of view. One must always bear in mind that impurities are present in most systems investigated. Nevertheless, the results known so far clearly show the pecularities of inisurfs compared to conventional initiators for emulsion polymerizations like water-soluble peroxides or AIBN. 

In conclusion we can say that the inisurfs known today have different chemical structures and consequently different properties. Experimental data are available showing that emulsion polymerization is posssible using inisurfs without any additional emulsifiers, thus reducing the electrolyte content in the latex serum as well as foam formation. From a more technical point of view problems existing today concern the low initiator efficiencies as well as the fact that the solid content of the latexes is restricted to approximately 40% without coagulum formation. 

A lot of mechanistic problems remain to be solved. It is not so clear, at the moment, why most of the inisurfs studied up to now have such a low efficiency, whatever their structure. On the other hand it is quite remarkable that, even with that low efficiency, they are able to allow the preparation of stable latexes under acceptable experimental conditions. Another problem is the control of the nucleation both with inisurfs and transurfs, there are indications that the particle number and size may not very sensitive to the amount of reactive surfactants, and more dependent on the amount of monomer used. Such behavior, up to now, has not been explainal Very few studies have been devoted to the reactivity of these surfactants, i.e., reactivity ratios for the surfmers, transfer constants for the transurfs and initiator efficiency for the inisurfs. Both the reactivities and the partition coefficient between the water and the organic phase have to be determined. In addition the reactivities may dependent on the other components of the recipe, for instance due to the effect of the ionic strength on the cmc. 

Figure 17.26. Structures of two inisurfs (a and b), i.e. polymerizable surfactants that also serve as polymerization initiators, and two transurfs (d and e), polymerizable surfactants with chain-tranfer capability. One conventional initiator (c) and one conventional chain-tranfer agent (f) are also given...

There is also surface active initiators which are called as "inisurfs", for example bis[2-(4 -sulfophenyl)alkyl]-2,2 -azodiisobutyrate ammonium salts and 2,2 -azobis(N-2 -methylpropanoyl-2-amino-alkyl-l-sulfonate)s. The initiators of this type carry stabilizing groups in their structures, and emulsion polymerization can be successfully carried out in the presence of them, without additional stabilizers up to more than 50% in solid content [37]. Moreover, the free radicals needed to initiate the emulsion polymerization can be produced by ultrasonically, or radiation-induced. Co y radiation is the most widely used as radiation-induced initiation system in the emulsion polymerizations. 

The general structures of new surface active initiators are given in Table 1 (A1 and A2). With both Inisurfs it is possible to carry out emulsion polymerizations without additional stabilizers up to more than 50% solid contents. In particular, structure A2 fulfills all of the demands with respect to chemical stability against hydrolysis and ease of preparation (one-step synthesis via a modified Ritter reaetion). Strueture A1 has still ester bonds, but a sulfonate instead of a sulfate hydrophilie group. The synthesis occurs via a two-step procedure where by the first step is the preparation of the corresponding bis(phenyl alkyl)-2,2 -azobisisobutyrates (Pinner reaction) and the second step is the sulfonation of the phenyl ring. 

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