Synthesis of Amphiphilic Polymers

Functionalisation with bulky hydrophobic carboxylic acids/DCC was studied for the synthesis of amphiphilic polymers based on dextran. Bile acid is covalently bound to dextran (Fig. 27) through ester linkage in the presence of DCC/DMAP (added in dichloromethane) as coupling reagent. 

More recently, the scope of using hyperbranched polymers as soluble supports in catalysis has been extended by the synthesis of amphiphilic star polymers bearing a hyperbranched core and amphiphilic diblock graft arms. This approach is based on previous work, where the authors reported the synthesis of a hyperbranched macroinitiator and its successful application in a cationic grafting-from reaction of 2-methyl-2-oxazoline to obtain water-soluble, amphiphilic star polymers [73]. Based on this approach, Nuyken et al. prepared catalyticaUy active star polymers where the transition metal catalysts are located at the core-shell interface. The synthesis is outlined in Scheme 6.10. 

So far, there have been only few reports about the synthesis of amphipolar polymer brushes, i.e. with amphiphilic block copolymer side chains. Gna-nou et al. [115] first reported the ROMP of norbornenoyl-endfunctionalized polystyrene-f -poly(ethylene oxide) macromonomers. Due to the low degree of polymerization, the polymacromonomer adopted a star-like rather than a cylindrical shape. Schmidt et al. [123] synthesized amphipolar cylindrical brushes with poly(2-vinylpyridine)-block-polystyrene side chains via radical polymerization of the corresponding block macromonomer. A similar polymer brush with poly(a-methylstyrene)-Wocfc-poly(2-vinylpyridine) side chains was also synthesized by Ishizu et al. via radical polymerization [124]. Using the grafting from approach, Muller et al. [121, 125] synthesized... 

Therefore, another idea is the synthesis of amphiphilic systems via radical polymerization using a two-phase or heterophase starting situation. In principle, these techniques allow the kinetic control of the copolymer structures or monomer sequence of the polymer chain. The final polymer chain is not only defined by the... 

CRP is a powerful tool for the synthesis of both polymers with narrow molecular weight distribution and of block copolymers. In aqueous systems, besides ATRP, the RAFT method in particular has been used successfully. A mrmber of uncharged, anionic, cationic, and zwitterionic monomers could be polymerized and several amphiphilic block copolymers were prepared from these monomers [150,153]. The success of a RAFT polymerization depends mainly on the chain transfer agent (CTA) involved. A key question is the hydrolytic stability of the terminal thiocarbonyl functionaHty of the growing polymers. Here, remarkable progress could be achieved by the synthesis of several new dithiobenzoates [150-152]. 

During ATRP, alkyl halides function as initiators while transition metal complexes (ruthenium, osmium, iron, copper and so on) act as the catalyst. Metal complexes are used to generate radicals (such as peroxide) via a one electron transfer process and during this process the transition metal becomes oxidised. Thus, ATRP is a reversible-deactivation radical polymerisation and can be employed to prepare polymers with similar molecular weight (MW) and low MW distribution. Advantages of ATRP are the ease of preparation, use of commercially available and inexpensive catalysts and initiators [14, 15]. The synthesis and process development of ATRP, as well as some new hybrid materials made of amphiphilic polymers, have been reported in the literature (Figure 2.3) [16, 17]. 

Peptides exhibit the highest antimicrobial activities of amphiphilic polymers and also possess antibacterial, antiviral, antifungi and anticancer activities [30-32]. In view of the potential applications of peptides, we will now discuss the synthesis of some important antibacterial peptides. Gad-1 and Gad-2 are peptides with amino acid chains and are prepared using O-fluorenylmethyloxycarbonyl (Fmoc) chemistry. 

Kang FIL, Liu WY, Fie BQ, Shen D, Ma L, Huang Y (2006) Synthesis of amphiphilic ethyl cellulose grafting poly(acrylic acid) copolymers and their self-assembly morphologies in water. Polymer 47 7927-7934... 

Chen, S., Alves, M., Save, M., Billon, L. Synthesis of amphiphilic diblock copolymers derived from renewable dextran by nitroxide mediated polymerization towards hierarchically structured honeycomb porous films. Polym. Chem. 5(18), 53105 (2014). doi 10.1039/ C4PY00390J... 

Scheme 3.5 Synthesis of amphiphilic cationic polymers ATRP.

Ravenelle F, Marchessault RH (2002) One-step synthesis of amphiphilic diblock copolymers from bacterial poly([/J]-3-hydroxybutyric acid). Biomacromolecules 3 1057-1064 Ravenelle F, Marchessault RH (2003) Self-assembly of poly([R]-3-hydroxybutyric aaA)-block-poly(ethylene glycol) diblock copolymers. Biomacromolecules 4 856-858 Renard E, Langlois V, Guerin P (2007) Chemical modifications of bacterial polyesters from stability to controlled degradation of resulting polymers. Corros Eng Sci Technol 42300-42310... 

Another difiinctional monomer, endo-cis-endo-hexacydo-[10.2.l.l .l .0 .0 ]heptadeca-6,13-diene was also used for the synthesis of star polymers. Using the arm-first approach, star polymers of norbomene, 5,6-bis (methox3methyl)norbomene (DMNBE) and 5,6-bis(dicarbotri-methylsilyloxy) norbomene (TMSNBE) were obtained. Amphiphilic star-block copolymers were prepared by reacting... 

Li et al. (2008a) introduced solvent-resistant multifunctional PV membranes based on segmented polymer networks (SPNs). Hydrophilic (acrylate)-terminated poly(ethylene oxide) was used as a macromolecular cross-linker of different hydro-phobic polyacrylates for the synthesis of amphiphilic SPNs. Multifunctional canposite membranes with thin SPN top layers were prepared by in situ polymerization. The support consisted of hydrolyzed PAN. These membranes were tested for dehydration of EtOH and isopropyl alcohol. The selectivity of the membranes greatly depended on the composition or the ratio of the hydrophilic and hydrophobic phases of the SPN. 

Nouvel C., Dubois R, DeUacherie E., Six J.L., Controlled synthesis of amphiphilic biodegradable polylactide-grafted dex-tran copolymers, J. Polym. ScL, Polym. Chem., 42(11), 2004,2577-2588. 

Iwakiri, N. Nishikawa, T. Kaneko, Y. Kadokawa, J.-L, Synthesis of Amphiphilic Polysiloxanes and Their Properties for Formation of Nano-Aggregates. Coll. Polym. Set 2009,287, 577-582. 

---