Micellization of double-hydrophilic copolymers

Hydrophilic-hydrophilic also called double-hydrophilic block copolymers, consist of water-soluble blocks of different chemical nature. In aqueous solution they behave as unimers like classical polymers or polyelectrolytes, whereas their amphiphilic characteristics, such as surface activity and micelle formation, only appear under the influence of a given external stimuli, mainly temperature, pH or ionic strength changes. Micellization of these copolymers can further be induced by complex formation of one of their blocks, either by electrostatic interaction with oppositely charged polymers, by hydrophobic interactions such as with surfactants, or by insolubilization in the presence of metal derivatives. These polymer intercomplexes, mainly polyion complexes (PIC), with their application possibilities will be outlined in more detail in Section 7.3.13. 

Typical examples of water-soluble block copolymers containing at least one non-ionic sequence are listed in Table 7.6. 

It can be noticed that the majority of copolymers in this category contain a PEO or a PVME sequence and that for completely non-ionic systems micellization is mainly induced by a temperature change. For those copolymers with an ionic and a non-ionic sequence micellization becomes also possible by pH changes or by addition of electrolytes. 

A second category of water-soluble block copolymers are those comprising two ionic sequences, either of the same type, for example anionic/anionic or cationic/cationic, or those of polyamphoKte types where one sequence is of anionic the other of cationic type. The corresponding examples are listed in Table 7.7. 

Within the first category, that non-ionic/ionic systems, PEO-P(M)AA is one of the most extensively studied. It has the particular feature of a polyelectrolyte, due to the P(M)AA sequence, in addition to the fact that PEO in aqueous medium has a lower critical solution temperature (LOST) which depends mainly on the pH and the concentration of electrolytes. Moreover it is well established that at low pH, PEO and P(M)AA interact strongly by hydrogen bonding, with formation of a hydrophobic interpolymer complex such as  

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