A Two-Step Colloidal Pathway to Polymer Composites

Polymer composites (blends) are prepared to control the mechanical properties of the polymeric materials and for obtaining permselective membranes for separation processes. Many polymer composites are, however, blends of incompatible polymers. Because of the tendency for segregation caused by the incompatibility, these materials can acquire a nonuniform structure. It is, therefore, useful to develop blends whose structure can be more uniform. 

In the methodology developed by us [24], the incompatibility of the two polymers was exploited in a positive way. The composites were obtained using a two-step method. In the first step, hydrophilic (hydrophobic) polymer latex particles were prepared using the concentrated emulsion method. The monomer-precursor of the continuous phase of the composite or water, when that monomer was hydrophilic, was selected as the continuous phase of the emulsion. In the second step, the emulsion whose dispersed phase was polymerized was dispersed in the continuous-phase monomer of the composite or its solution in water when the monomer was hydrophilic, after a suitable initiator was introduced in the continuous phase. The submicrometer size hydrophilic (hydrophobic) latexes were thus dispersed in the hydrophobic (hydrophilic) continuous phase without the addition of a dispersant. The experimental observations indicated that the above colloidal dispersions remained stable. The stability is due to both the dispersant introduced in the first step and the presence of the films of the continuous phase of the concentrated emulsion around the latex particles. These films consist of either the monomer-precursor of the continuous phase of the composite or water when the monomer-precursor is hydrophilic. This ensured the compatibility of the particles with the continuous phase. The preparation of poly(styrenesulfonic acid) salt latexes dispersed in cross-linked polystyrene matrices as well as of polystyrene latexes dispersed in crosslinked polyacrylamide matrices is described below. The two-step method is compared to the single-step ones based on concentrated emulsions or microemulsions. 

For the preparation of polystyrene latexes, the compositions listed in Table 11 were employed. The molecular weight and conversion after 24 h of 

Composition for the preparation of poly(styrenesulfonic acid) salt latexes Dispersed phase 

The compositions of the prepared polymer composites are listed in Tables 13 and 14. 

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