An Improved Concentrated Emulsion Polymerization Pathway

The main condition for the use of concentrated emulsions as precursors for polymers, copolymers, and polymer composites is the stability of the gel at the 

In the first step, the hydrophobic monomer was partially polymerized in bulk, using AIBN as initiator, by heating at 50 °C until a small conversion was reached. Then the inhibitor methylhydroquinone (MEHQ) was introduced to terminate polymerization. In the second step, the partially polymerized monomer was injected at room temperature into a small amount of a stirred aqueous solution of SDS to generate a concentrated emulsion. 

The first step in the preparation of a polymer was the same as that used for the preparation of a two-step concentrated emulsion, but without introducing MEHQ at the end of the partial polymerization step. Subsequently the concentrated emulsion was subjected to polymerization by heating at 50 °C for 50 h. 

The amounts of the components involved in the concentrated emulsions are listed in Table 8. The weight percent of bulk phases separated from the concentrated emulsions prepared at room temperature and heated at 50 °C for 24 h is considered a measure of its stability. The weight percent of bulk phase separated from the concentrated emulsions prepared in one step at room temperature, in the absence of initiator, and subsequently heated for 24 h at 50 °C is presented in Table 9, which also contains the values of the interfacial tension, y, measured at room temperature, between the hydrophobic monomer and water, in the absence of surfactant. It should be noted that the stability of the concentrated emulsion is almost unaffected by the presence of AIBN and MEHQ. Table 9 shows that in the one-step method the stability is highest for styrene and lowest for MMA, and that the stability increases with increasing interfacial tension between water and monomer in the absence of surfactant. 

The concentrated emulsion free of MEHQ prepared at room temperature can be further polymerized by heating at 50 °C for 50 h. Several polymers, copolymers, and polymer composites were prepared by the two-step method. The amounts of components employed to prepare copolymers and polymer composites are listed in Table 10, whereas the amounts of components employed to prepare polymers are those in Table 8 (of course without MEHQ). The one-step pathway of the corresponding materials was also employed. In the latter case, very high phase separations occurred in most systems, except those 

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