Hydrophobic poly chains

The pioneering work on amphiphilic polyelectrolytes goes back to 1951, when Strauss et al. [25] first synthesized amphiphilic polycations by quaternization of poly(2-vinylpyridine) with n-dodecyl bromide. They revealed that the long alkyl side chains attached to partially quaternized poly(vinylpyridine)s tended to aggregate in aqueous solution so that the polymers assumed a compact conformation when the mole fraction of the hydrophobic side chains exceeded a certain critical value. Thus, Strauss et al. became the first to show experimentally the intramolecular micellation of amphiphilic polymers and the existence of a critical content of hydrophobic residues which may be compared to the critical micelle concentration of ordinary surfactants. They called such amphiphilic polyelectrolytes polysoaps [25],... 

Solubilization of a graft copolymer comprising a hydrophobic poly(dodecyl-methacrylate) backbone and hydrophilic poly(ethylene glycol) monomethyl ether side chains in water/AOT/cyclohexane w/o microemulsions was rationalized in terms of the backbone dissolved in the continuous apolar phase and the side chains entrapped within the aqueous micellar cores [189],... 

Hydrophobic side chain polyamides from N,N-didodecylamine and sodium poly aery late or polyacrylic acid [1240]... 

Fig. 3. Alignment of poly(HA) depolymerase catalytic active amino acids. Amino acids of the catalytic triad and the conserved histidine residue of the putative oxyanion are shown in bold letters. The positions (pos.) of respective amino acids of mature depolymerase proteins are indicated. Amino acids conserved in all poly(HASCL) depolymerases are indicated in capital letters, those which have been conserved in ten or more proteins are marked by low letters in the consensus sequence. indicates amino acids with hydrophobic side chains + indicates amino acids with a small side chain...

Table 4. Formation of solid-state complexes between cyclodextrins and hydrophobic poly-mers/oligomers with various chain sectional area... 

Figure 11.8 Stmctuies of (a) patent poly(piopylene imine) dendrimer and (h) fully quaternized form, which presents hoth hydrophilic triethyleneoxy methyl ether (TEO) and hydrophobic octyl chains at every terminal position.

According to the results shown for these polymers, the effect of the side chain structure on the viscoelastic and thermal behavior, play an important role. The effect of the carboxylic group by one hand and the length of the hydrophobic side chain on the other, are the driving forces responsible of the relaxational behavior in this family of poly(itaconate)s. 

TX-45, TX-114, TX-100 have the same hydrophobic group (4-(l,l,3,3-tet-ramethylbutyl)phenyl), but have different lengths of hydrophilic poly ethoxy 1 chain, i.e. n = 5, 7.5 and 10, respectively (Scheme 4.6) Tween 20 and Tween 80 have the same molecular structure and EO number, while differentiate in the hydrophobic alkyl chain length. It is well known that the smaller the Henry s constant, the larger the solubility. The Henry s constants of C02 (e.g., 25 °C) in the surfactants with more EO content are smaller (TX-45 39.8 > TX-114 28.7 > TX-100 20.0), while the effect of alkyl chain length on the Henry s constant is very limited (Tween 20 10.7 and Tween 80 10.1). The absolute value of the enthalpy increases considerably with increasing EO content (TX-45 -14.5 2.1, TX-114 -15.9 2.3 and TX-100 -20.4 1.6) [83]. 

Upon ultraviolet irradiation, trans CHP isomerized to the cis form (around 10%), and the aqueous solution viscosity decreased as much as 80%. The conformation change was interpreted as follows. The anionic linear and planar eA -trans CHP would attach itself to the hydrophobic poly(methacrylic add) backbone, teading to an extended polymer conformation. In the cis form, azo-dyes are much more hydrophilic. Consequently, the cis form was envisaged as binding less strongly so that the polymer chain would be less extended. 

Those nanoparticles (3LNPs) were fabricated via a pH-controlled hierarchical self-assembly of a tercopolymer brush (Schemes 10.2 and 10.3), which contained hydrophilic polycaprolactone (PCL) chains, water-soluble PEG chains, and pH-responsive poly[2-(iV,iV-diethylamino)ethyl methacrylate] (PDEA) chains. PDEA is a polybase that is soluble at low pH but insoluble at neutral pH [167-169]. The brush polymer was initially dispersed in a pH 5.0 solution where the PDEA chains were protonated and hence water-soluble. The hydrophobic PCL chains and drug molecules associated to form the hydrophobic core. The PEG and protonated PDEA chains formed a hydrophilic corona surrounding the core. After the solution pH was raised to 7.4, the PDEA chains were deprotonated and became hydrophobic, collapsing on the PCL core as a hydrophobic middle layer with only the PEG chains forming the hydrophilic corona (Scheme 10.3). 

Polymers are also essential for the stabilisation of nonaqueous dispersions, since in this case electrostatic stabilisation is not possible (due to the low dielectric constant of the medium). In order to understand the role of nonionic surfactants and polymers in dispersion stability, it is essential to consider the adsorption and conformation of the surfactant and macromolecule at the solid/liquid interface (this point was discussed in detail in Chapters 5 and 6). With nonionic surfactants of the alcohol ethoxylate-type (which may be represented as A-B stmctures), the hydrophobic chain B (the alkyl group) becomes adsorbed onto the hydrophobic particle or droplet surface so as to leave the strongly hydrated poly(ethylene oxide) (PEO) chain A dangling in solution The latter provides not only the steric repulsion but also a hydrodynamic thickness 5 that is determined by the number of ethylene oxide (EO) units present. The polymeric surfactants used for steric stabilisation are mostly of the A-B-A type, with the hydrophobic B chain [e.g., poly (propylene oxide)] forming the anchor as a result of its being strongly adsorbed onto the hydrophobic particle or oil droplet The A chains consist of hydrophilic components (e.g., EO groups), and these provide the effective steric repulsion. 

A new polymeric amphiphile based on cationic poly(L-lysine), which was partially modified with hydrophobic palmitoyl chains and hydrophilic neutral methoxy-poly(ethylene glycol) (Fig. 7e), was introduced by Uchegbu et al. [38,39], In water in the presence of cholesterol, these copolymers assembled into vesicles with diameters ranging from 200 to 600 nm (DLS, freeze-fracture TEM), depending on the chemical composition of the copolymer and the length of the polypeptide backbone. More detailed information about the secondary structure of chains and the structure of vesicle membranes were not given. 

NMR spectroscopic analysis finally proved that the poly(ethylene oxide) blocks are firmly anchored in the inorganic phase rather than being located at the interphase adjacent to the hydrophobic domains. Solid-state NMR spectroscopy revealed that this anchoring leads to a substantial hindrance of the conformational mobility in the poly(ethylene oxide) chains compared with the relatively mobile hydrophobic poly(isoprene) [44]. 

Two possible scenarios can be envisaged for the structure of the hybrid material (see Fig. 11). The poly(ethylene oxide) block, albeit strongly interacting and partially penetrating, forms a pure PEO layer at the interface to the hydrophobic poly(isoprene) (Fig. 11, left-hand sketch) ( three-phase system). The other possibility is the complete dissolution of the PEO chains in the aluminosilicate, which results in the two-phase system depicted in the right-hand sketch of Fig. 11. Spin-diffusion NMR experiments showed that there appears to be no dynamic heterogeneity in the poly(ethylene oxide) chains, as would be expected for a three-phase system, giving rise to the conclusion that the hydrophilic... 

Similarly, Wasserman and coworkers have studied a wide selection of polymeric materials in aqueous solution that are associative of some kind, i.e., that form some sort of self-assembly through non-covalent interactions [96]. Their study mainly deals with hydrogels of hydrophobically modified polymers, aqueous solutions of polymeric micelles created by block copolymers, and hydrogels based on poly (acrylic acid) and macrodiisocyanates. The spin probes of choice were hydrophobic, such as 5- and 16-DSA (see Eig. 2) or even spin labeled polymers. It was, e.g., possible to screen for the effect of chemical stmcture on the gel formation by recording and understanding the local mobility of the hydrophobic, long chain spin probes as a function of temperature. 

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