Intrapolymer self-association

Hydrophobic associations in random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate and some methacrylamides and methacrylates substituted with bulky hydrophobes are described with a focus on preferential intrapolymer self-association which leads to the formation of single-macromolecular assemblies (i.e., unimolecular micelles). Structural parameters that critically determine the type of the macromolecular association (i.e., intra- vs. interpolymer associations) are discussed, which include the type of hydrophobes, their content in a polymer, sequence distribution of electrolyte and hydrophobic monomer units, and the type of spacer bonding. Functionalization of single-macromolecular assemblies with some photoactive chromophores is also presented. 

This chapter will discuss hydrophobic associations in random copolymers of AMPS and some hydrophobic methacrylamide and methacrylate comonomers with a focus on the intra- versus interpolymer self-association in connection witih the type of hydrophobes, their content in the polymers, and spacer bonding. A particular emphasis will be placed on intrapolymer association of hydrophobes which leads to single-molecular self-assemblies. Functionalization of the single-macromolecular assemblies with some photoactive chromophores will also be presented briefly. 

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 the random copolymers shown in Scheme 1, hydrophobic associations occur completely in an intrapolymer mode [20-22] hence, the polymers form unimer micelles independent of the polymer concentration in water. The sequence distribution of electrolyte and hydrophobic monomer units in the polymer chain is a critical structural factor to determine whether the hydrophobic self-associations are an intra- or interpolymer mode. Block sequences of hydrophobic units have a strong tendency for interpolymer association, whereas random and alternating sequences tend to associate in an intrapolymer mode [20-22]. Even a subtle difference in the sequence distribution in random copolymers has a significant effect on the self-association mode [23]. If the sequence distribution is blocky in nature, there is a propensity for interpolymer association. Other important structural factors that induce polymers to form unimer micelles are that the hydrophobic groups should be bulky and have cyclic structures, such as cyclododecyl, adamantyl, and naphthyl groups, and their contents in the copolymers should be higher than about 30 mol%, as shown in Scheme 1 [20-22]. In addition. 

Important evidence for intrapolymer self-organization to form unimer micelles is that the Stokes radius is independent of the concentration. If interpolymer association occurs, the size of the aggregate should increase sig-... 

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