Hydrophobic association amphiphilic random copolymers

General Considerations of Hydrophobic Associations in Amphiphilic Random Copolymers. 

Figure 1. Conceptual illustration of hydrophobic association of amphiphilic random copolymers.

In general, unimer micelles are preferentially formed in highly dilute aqueous solutions. As the concentration is increased, however, the hydro-phobic association may not necessarily be an intrapolymer event. If interpolymer open associations occur between the hydrophobes or between the primary micelle units, multipolymer aggregates would be formed instead of the unimer micelles. Whether the intrapolymer closed association predominates over the interpolymer open association depends on primarily the chemical structure or the first-order structure of amphiphilic random copolymers. 

As the number of hydrophobic sequences in an amphiphilic polymer chain increases, intrapolymer hydrophobic association, as well as interpolymer association, becomes an important process to determine overall self-organized structures. This is particularly so with amphiphilic random or alternating copolymers in which hydrophobic and hydrophilic units are randomly or alternately distributed on a polymer chain. Intrapolymerassociating structures are of critical importance to determine interpolymerassociating structures. In general, intrapolymer hydrophobic association is dominant in dilute solutions, whereas interpolymer association also occurs in a semidilute or concentrated regimen. In random copolymers with a strong tendency for intrapolymer association, unimolecular micelles (unimer micelles) may be formed as a consequence of intrapolymer closed association. 

In this review, hydrophilically and hydrophobically modified poly(N-iso-propylacrylamide) (PNIPAM) copolymers are mainly used to illustrate how amphiphilic copolymer chains can fold from an extended random coil to a collapsed globule in extremely dilute solutions and associate to form a stable mesoglobular phase which exists between single-chain globules and macroscopic precipitation. The copolymers used can be prepared by free-radical reaction. 

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