Amphiphilic random copolymers

The polymers were synthesised from boc-protected amine monomers and alkyl or benzyl methacrylate monomers. The polymerisation was performed by applying AIBN, as a radical initiator, and methyl 3-mercaptopropionate, as a chain transfer agent, in acetonitrile. The treatment of boc-protected polymers with TFA produced amphiphilic random copolymers with cationic ammoninm groups in the side chains. 

Honglawan, A., Yang, S. Evaporative assembly of ordered microporous films and their hierarchical structures from amphiphilic random copolymers. Soft Matter 8, 11897-11904 (2012)... 

General Considerations of Hydrophobic Associations in Amphiphilic Random Copolymers. 

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

This chapter deals with a recently developed unimer micelle, a novel intramolecular assembly with a higher-order structure, formed from tailored amphiphilic random copolymers bearing charge and bulky hydrophobes. The first half of this chapter will be devoted to the synthesis of such amphiphilic poly electrolytes and characterization of the unimer micelle. The functionalization of the unimer micelles with chromophoric molecules and some functional properties of these functionalized unimer micelles will be described in some detail in the second half of this chapter. 

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 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]. 

A polymer is considered to be a copolymer when more than one type of repeat unit is present within the chain. There are a variety of copolymers, depending on the relative placement of the different types of repeat units. These are broadly classified as random, block, graft, and alternating copolymers (see Fig. 2.1 for structural details Cheremisinoff 1997 Ravve 2000 Odian 2004). Among these stmctures, block copolymers have attracted particular attention, because of their versatility to form well-defined supramolecular assemblies. When a block copolymer contains two blocks (hydrophobic and hydrophilic), it is called an amphiphilic diblock copolymer. The immiscibility of the hydrophilic and lipophilic blocks in the polymers provides the ability to form a variety of assemblies, the stmctures and morphologies of which can be controlled by tuning the overall molecular weight and molar ratios of the different blocks (Alexandridis et al. 2000). 

In a dilute solution, when the polymer is in a coil state (Fig. 6a), the diffusion of hydrophobic particles into the coil is normally faster than the chemical reaction [53]. In this case, the local concentration of particles H inside the coil is practically the same as in the bulk. Therefore, we expect that at the initial stage, the reaction will lead to a random copolymer some of the P monomeric units will attach to H reagent and thereby they will acquire amphiphilic (A) properties P + H —A (Fig. 6b). As long as the number of modified A units is not too large, the chain remains in a swollen coillike conformation (Fig. 6b). However, when this number becomes sufficiently large, the hydrophobically modified polymer segments would tend to form... 

Besides the polypeptide hybrid block copolymers described earlier, there exist a few examples of purely peptide-based amphiphiles and block/random copolymers (copolypeptides) (Fig. 10). In the latter case, both the core and corona of aggregates consist of a polypeptide. Any of the studies reported so far dealt with aggregation in aqueous media. 

The non-amphiphilic polymers can be widely considered as homopolymers or random copolymers. Most of the studies focussed on water-soluble polymers, but some studies on oil-soluble polymers exist as well. The water-soluble polymers can be uncharged or... 

A considerable amount of work has focused on the design and synthesis of macromolecules for use as emulsifiers for lipophilic materials and as polymeric stabilizers for the colloidal dispersion of lipophilic, hydrocarbon polymers in compressed CO2. It has been shown that fluorinated acrylate homopolymers, such as PFOA, are effective amphiphiles as they possess a lipophilic acrylate-like backbone and C02-philic, fluorinated side chains, as indicated in Figure 4.5-1 [100]. Furthermore, it has been demonstrated that a homopolymer which is physically adsorbed to the surface of a polymer colloid precludes coagulation due to the presence of loops and tails [110]. These fluorinated acrylate homopolymers can be synthesized homogeneously in CO2 as described in an earlier section. The solution properties [111,112] and phase behavior [45] of PFOA in SCCO2 have been thoroughly examined. Additionally, the backbone of these materials can be made more lipophilic in nature by incorporating other monomers to make random copolymers [34]. 

Figure 3.3 Synthesis of methacrylate random copolymers with cationic amphiphilic structures containing R hydrophobic groups (methyl, ethyl, butyl, hexyl and benzyl groups). AIBN azobisisobutylonitrile, RT room temperature and TFA trifluoroacetic acid. Reprodnced with permission from H. Takahashi,...

SHA Sharma, S.C., Acharya, D.P., Garcia-Roman, M., Itami, Y., and Kunieda, H., Phase behavior and surface tensions of amphiphilic fluorinated random copolymer aqueous solutions, Coll. Surfaces A, 280, 140, 2006. 

Li Y, Deng Y, Tong X, Wang X. 2006. Formation of photoresponsive uniform colloidal spheres from an amphiphilic azobenzene containing random copolymer. Macromole... 

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