Charged Hydrophobic Copolymers

Hydrophobic polyelectrolytes (HPEs) are polymers composed of covalently bonded sequences of polar (ionizable) groups which are soluble in water and hydrophobic groups which are not. This unique duality towards an aqueous environment leads to a rich spectrum of complex self-association phenom- 

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Khokhlov AR, Khalatur PG (2005) Solution properties of charged hydrophobic/hydrophilic copolymers. Curr Opin Colloid Interface Sci 10 22-29. doi 10.1016/j.cocis.2005.04.003... 

The charged segments of the AMPS units in these amphiphilic copolymers effectively solubilize the sequences of hydrophobic monomer units to water. In fact, the copolymers ASt-72 (7 with x = 72), APh-50 (8 with x = 50), APy-50 (9 with x = 50), and ALa-44 (10 with x = 44) were all soluble in water. The copolymer ACh-x was a little less water soluble ACh-23 (11 with x = 23) was almost soluble, whereas ACh-60 was insoluble. All these copolymers were soluble in methanol, N, AT-dimethylformamide, and dimethylsulfoxide, but insoluble in most of other common organic solvents. 

Block copolymer micelles with a polyelectrolyte corona are a very important class of colloidal particles in aqueous medium and are often referred to as polyelectrolyte block copolymer micelles. The micellization behavior of these charged micelles has been very recently reviewed by Riess [14] and FOrster et al. [15]. A brief overview of the topic will therefore be presented in what follows. Amphiphilic block copolymers consisting of one hydrophobic block linked to one ionic block will only be discussed in this section. Blocks copolymers containing one hydrophilic block and one ionic block will be discussed in Sect. 4.3. 

The temperature-induced behavior of copolymers at two pHs (4.0 and 7.4) is observed as shown in Figure 8. At pH 4, no LCST was observed with poly-DMAEMA, and the LCST of all copolymers was increased compared to that at pH 7.4. At pH 4.0, (A,A-dimethylamino)ethyl groups of DMAEMA are fully ionized. An increasing electrostatic repulsion between charged sites on DMAEMA disrupts the hydrogen bonds between EAAm and DMAEMA. These interfere with the hydrophobic interactions between (A,A-dimethyl-... 

As mentioned in Sect. 2.2.3, the biodistribution of HPMA copolymers depends on many factors. Molecular weight influences the uptake in the isolated tissue of yolk sac [266] as well as the elimination in vivo [124, 125,267,268]. Nonspecific increase in the rate of polymer uptake can be achieved by incorporation of positively charged or hydrophobic comonomers into the HPMA copolymer structure, such as methacryloyloxyethyltrimethylammonium chloride [22], N-methacryloyltyrosinamide [21], or N-[2-(4-hydroxyphenyl)ethyl]acrylamide [267]. The incorporation of hydrophobic moieties may influence the solution properties of the HPMA copolymer conjugates [132,134,269]. The interaction with the cellular surface may depend on the association number and the stability of the micelles. 

In ionic block copolymers, micellization occurs in a solvent that is selective for one of the blocks, as for non-ionic block copolymers. However, the ionic character of the copolymer introduces a new parameter governing the structure and properties of micellar structures. In particular, the ionic strength plays an important role in the conformation of the copolymer, and the presence of a high charge density leads to some specific properties unique to ionic block copolymers. Many of the studies on ionic block copolymers have been undertaken with solvents selective for the ionic polyelectrolyte block, generally water or related solvents, such as water-methanol mixtures. However, it has been observed that it is often difficult to dissolve ionic hydrophilic-hydrophobic block copolymers in water. These dissolution problems are far more pronounced than for block copolymers in non-aqueous selective solvents, although they do not always reflect real insolubility. In many cases, dissolution can be achieved if a better solvent is used first and examples of the use of cosolvents are listed by Selb and Gallot (1985). 

Takahashi et al.67) prepared ionene-tetrahydrofuran-ionene (ITI) triblock copolymers and investigated their surface activities. Surface tension-concentration curves for salt-free aqueous solutions of ITI showed that the critical micelle concentration (CMC) decreased with increasing mole fraction of tetrahydrofuran units in the copolymer. This behavior is due to an increase in hydrophobicity. The adsorbance and the thickness of the adsorbed layer for various ITI at the air-water interface were measured by ellipsometry. The adsorbance was also estimated from the Gibbs adsorption equation extended to aqueous polyelectrolyte solutions. The measured and calculated adsorbances were of the same order of magnitude. The thickness of the adsorbed layer was almost equal to the contour length of the ionene blocks. The intramolecular electrostatic repulsion between charged groups in the ionene blocks is probably responsible for the full extension of the... 

Dan, N. and M. Tirrell. 1993. Self-assembly of block copolymers with strongly charged and a hydrophobic block in a selective, polar solvent. Micelles and adsorbed la ifasromolecule 6 4310—4315. 

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