Polymer-based self-assembly

The above examples illustrate some of the various methods and motifs by which small molecules can undergo self-organization and hierarchical self-assembly to form complex materials with important properties. The self-assembly exhibited by small molecules often gives rise to extended order in one or more directions, over relatively long distances. Polymers also exist as extended structures over long distances and, as such, are an important venue for probing self-assembly on the macromolecular scale. 

The hierarchical self-organization exhibited routinely by Nature and subsequently mimicked by chemists in the laboratory has opened up the field to a wide variety of potential applications and new methodology in the field of chemistry to which these concepts can be applied. Synthetic polymers can also exhibit several types and hierarchical levels of self-assembly, including (1) main-chain extension based on molecular self-assembly resulting in the formation of high molecular 

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As mentioned earlier, the contact-mechanics-based experimental studies of interfacial adhesion primarily include (1) direct measurements of surface and interfacial energies of polymers and self-assembled monolayers (2) quantitative studies on the role of interfacial coupling agents in the adhesion of elastomers (3) adhesion of microparticles on surfaces and (4) adhesion of viscoelastic polymer particles. In these studies, a variety of experimental tools have been employed by different researchers. Each one of these tools offers certain advantages over the others. These experimental studies are reviewed in Section 4. 

As reviewed so far, the contact-mechanics-based techniques (JKR and SFA methods) have been effective in the understanding molecular level mechanisms related to the adhesion of elastomers and in measuring the surface and interfacial energies of polymers and self-assembled monolayers. The current work in this area is aimed at understanding contact induced interfacial rearrangements and the role of specific interactions. The recent progress of these studies is discussed in this section. 

Fig. 7.16 Multi-step main-chain self-assembly to form a flexible, high molecular weight polymer. Step 1 dimerization of bifunctional unit via the self-complimentary ureidopyrimidinone end (top). Step 2 addition of a metal salt such as iron(ll) initiates metal coordination-based self-assembly of the trpy-functionalized ends to form extended polymer chains (bottom).

In 2004, Week and co-workers demonstrated that both mono- and multifunctional self-assembly could be employed simultaneously independently and reversibly on the same side-chain functionalized polymer [96]. A random terpolymer of poly(norbornene) was synthesized consisting of diaminopyridine (DAP) hydrogen-bonding receptors and a palladium-functionalized SCS-type pincer ligand for metal coordination-based self-assembly (Fig. 7.18). 

Based on the studies of organic block co-polymers, PFS block co-polymers should self-assemble in solvents, which are selective for one of the blocks. In the case of organic block co-polymers, most studies have led to the identification of spherical structures where the less-soluble block constitutes the core within a corona formed by the more-soluble block. Only since the mid-1990s have non-spherical structures become more commonly reported. " ... 

The non-cross-linked poly(acrylamide) 79 bearing the triarylphosphino groups was prepared from the acrylamide monomer and diphenyl(styryl) phosphine. The metal-directed self-assembly process between the non-cross-linked polymer ligand 79 and the palladium species afforded the networked supramolecular complex 80 [106, 109]. The complex catalyzed the Suzuki-Miyaura coupling [106,109] and the same concept, a tungsten-based self-assembly complex, has also been developed for the catalytic oxidation process. 

Huang F, Nagvekar DS, ZhouX, Gibson HW. Formation ofa linear supramolecular polymer by self-assembly of two homoditopic monomers based on the bis(m-phenylene)-32-crown-lO/paraquat recognition motif. Aiacromolecules. 2007 40 3561—3567. 

Alternatively, the gold electrode can be modified with a thiol-based self-assembled monolayer (SAM) bearing functional groups suitable to bind DNA [118], Often this binding is performed via a coupling reagent such as l-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), which enables aminated or carboxylated DNA to bond with the appropriately carboxylated or aminated functional group on the electrode [119], or on a polymer deposited on the electrode... 

An attempt to provide a rationale to the features related to the self-assembly has been reported in a recent paper that has faced the investigation of thermodynamic parameters, in particular entropic terms, which are drivers for the polymer nanopardcle self-assembly, with a theoredcal approach based on fluids density functional theory (DFT) calculations [12]. 

To make amino-group functionalized PPEs, which will be positively charged and therefore have potential for nucleic add delivery, the functional phosphoester monomer 2-(N-tert-butoxycarbonyla-mino)ethoxy-2-oxo-l,3,2-dioxaphospholane (PEEABoc) (17) has been synthesized. Based on the ROP of PEEABoc using hydroxyl-terminated MPEG-b-PGL as the macroinitiator, an amphiphilic and cationic triblock copolymer consisting of MPEG, PCL, and poly(2-aminoethyl ethylene phosphate) has been developed, which is denoted mPEG-b-PCL-f -PPE-EA (eqn [10]). This amphiphilic polymer can self-assemble into nanopartides in aqueous solution and absorb siRNA for RNAi-based therapy. 

A few studies have been carried out preparing core-shell composite polymers by using heterocoagulation based on hydrophobic interactions [82,83], It was found that the morphology of the heterocoagulates was dependent on the solid content of the polymer dispersion, self-assembly time and electrolyte concentration. Hydrogen bonding and k-k interactions are the common... 

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