SYNTHESIS OF SPONGE-LIKE POLYMER DISPERSIONS VIA POLYMERIZATION OF BICONTINUOUS MICROEMULSIONS

Polymer gels with high water content are made by polymerization of hyd rophilic/hydrophobic monomer mixtures in bicontinuous microemulsions. These structures can be described as a heterophasic, bicontinuous poly mer colloid-in-water structure, the characteristic length of which is only indirectly influenced by the original microemulsion mixture. The structure formation and phase changes throughout the polymerization re action are followed with rheology, polarization microscopy, and scanni ng and transmission electron microscopy. It is shown that already the very first formed polymer changes disturb the bicontinuous phase struc ture and nucleate a vesicular phase; with further consumption of the m onomer mixture, at least three other phase transitions can be detected , ending with a simple globular surfactant structure. Although direct templating of the original mesomorphous structure does not occur, the existence of the diverse lyotropic phases influences the final structu re. It is shown that simple dilution changes the characteristic length of the network elements from about 2 mu m down to 50 nm. This is expl ained by a combination of a nucleation-and-growth mechanism with the i nfluence of a restricted colloidal stability in anisometric lyotropic phases.