Aggregation of copolymers

The second possible geometry will arise if the micellization proceeds by aggregation of copolymer chains that already have a glassy head. Although little is known about the structure of individual glassy chains in solution, the characteristic relaxation time ofthe chain is likely to depend on the amount of solvent actually present in the collapsed globule. In the extreme case of zero solvent... 

Figure 11 Scanning electron microscopy images of bundle-like (a) and spherical (b) aggregates of copolymer 45 with short and long PAN units, respectively. Reproduced with permission from Ajioka, N. Yokoyama, A. Yokozawa, T. Macromol. Rapid Commun. 2008, 29, 665-671, Copyright Wiley-VCH Verlag GmbH Co. KGaA. ...

Figure 32 Schematic representation of a nematic aggregation of copolymer assemblies involving seven molecules each with a side-by-side shift of one-fourth of the length and alternating orientations. (Reprinted from R Cavalleri, A. Ciferri, C. Dell Erba, M. Novi, and B. Purevsuren. Macrolmolecules 30 3513, 1997. Copyright [1997] American Chemical Society. With permission.)...

Kobayashi and coworkers further developed a new immobilizing technique for metal catalysts, a PI method [58-61]. They originally used the technique for palladium catalysts, and then applied it to Lewis acids. The PI method was successfully used for the preparation of immobilized Sc(OTf)3. When copolymer (122) was used for the microencapsulation of Sc(OTf)3, remarkable solvent effects were observed. Random aggregation of copolymer (122)-Sc(OTf)3 was obtained in toluene, which was named as polymer incarcerated (PI) Sc(OTf)3. On the other hand, spherical micelles were formed in THF-cyclohexane, which was named polymer-micelle incarcerated (PMI) Sc(OTf)3.. PMI Sc(OTf)3 worked well in the Mukaiyama-aldol reaction of benzaldehyde with (123) and showed higher catalytic activity compared to that of PI Sc(OTf)3 mainly due to its larger surface area of PMI Sc(OTf)3. This catalyst was also used in other reactions such as Mannich-type (123) and (125) and Michael (127) and (128) reactions. For Michael reactions, inorganic support such as montmorilonite-enwrapped Scandium is also an efficient catalyst [62]. 

Freeze fracture has been used to study the structure of colloidal particles in water-oil mixtures stabilized by polymer emulsifiers. Microemulsions consisting of water, toluene, and graft copolymer composed of a polystyrene backbone and a PEO graft were deposited onto a small gold plate, quenched in liquid nitrogen in equilibrium with its own solid phase [582]. Replicas of the fractured surfaces were washed with tetra-hydrofuran, which showed the micellar structure of the copolymers. Classical microemulsions have been studied [583], and micellar aggregates of copolymers have been shown [584, 585]. Polymer latexes have been prepared using simUar methods by Sle)rtr and Robards [586]. The emphasis in this review was on the plastic deformation observed in the fi eeze fracture method and in ultrathin frozen sections. 

Though the polymerization system was uniformly emulsified at the beginning, it became progressively unstable as the polymerization proceeded, phase separation showed up, and in the final step, aggregation of copolymer occurred. We consider that the decrease in the optical activity of polymer with the progress of polymerization is a direct consequence of these modifications of the system. Nevertheless our results favor the conclusion that in... 

Polymers in Solution. Polyacrylamide is soluble in water at all concentrations, temperatures, and pH values. An extrapolated theta temperature in water is approximately —40° C (17). Insoluble gel fractions are sometimes obtained owing to cross-link formation between chains or to the formation of imide groups along the polymer chains (18). In very dilute solution, polyacrylamide exists as unassociated coils which can have an eUipsoidal or beanlike stmcture (19). Large aggregates of polymer chains have been observed in hydrolyzed polyacrylamides (20) and in copolymers containing a small amount of hydrophobic groups (21). 

It represents the critical St content in the copolymer in the sense that it is the onset of progressive self-aggregation of the St groups. 

As has been described in Chapter 4, random copolymers of styrene (St) and 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) form a micelle-like microphase structure in aqueous solution [29]. The intramolecular hydrophobic aggregation of the St residues occurs when the St content in the copolymer is higher than ca. 50 mol%. When a small mole fraction of the phenanthrene (Phen) residues is covalently incorporated into such an amphiphilic polyelectrolyte, the Phen residues are hydrophobically encapsulated in the aggregate of the St residues. This kind of polymer system (poly(A/St/Phen), 29) can be prepared by free radical ter-polymerization of AMPS, St, and a small mole fraction of 9-vinylphenanthrene [119]. 

Aggregation of Block Copolymer Surfactants 3.1 Tethering Processes... 

The vesicles made from lipid bilayers are analogous to polymersomes, which are vesicles formed from high molecular weight amphiphilic block copolymers [94—96], Unlike the micelles discussed earlier from the similar copolymer components, the presence of bilayer walls formed from the aggregation of hydrophobic domains provides new properties. They can be designed to respond, for example, by opening or by disassembly, to external stimuli such as pH, heat, light, and redox processes [97]. This makes them usable as scaffolds for cascade reactions, even those with combinations of enzymes [98, 99]. 

Zhang L, Eisenberg A (1995) Multiple morphologies of crew-cut aggregates of polystyrene-6-poly(acrylic acid) block copolymers. Science 1268 1728-1731... 

Fig. 16 The thermal response of different polymeric structures based on PVCL and the amphiphilic macromonomer MAC11EO42. Left Shrinking of the grafted PVCL microgel. Right Heat-induced aggregation of the graft copolymer and formation of a mesoglobule [181]...

---