Chain-multi-functionalization

Hirao et al. have further developed the above functionahzation reactions using DPE derivatives in an excellent procedure referred to as the chain-multi-functionalization of living anionic polymers [176]. For this purpose, a new DPE derivative, l,l-bis(3-terFbutyldimethylsilyloxymethylphenyl)ethylene (12). has been synthesized. This DPE is designed in such a way that the tert-butyldimethylsilyl ether acts as a protected functionality in a reaction with living anionic polymers, and is quantitatively transformed into a benzyl bromide (BnBr) or even chloride and iodide functions [176, 183]. As illustrated in Scheme 5.18,12 was first reacted with PSLi to introduce two silyl ether functionalities at the chain-end, followed by treatment with Me3SiCl/LiBr to transform into two BnBr fimctions as a result, a well-defined chain-end-(BnBr)2-functionalized PS was obtained. The same functionalized DPE-derived anion was then separately synthesized, and reacted with the above chain-end-(BnBr)2-functionalized PS. The four silyl ether functionalities thus introduced were transformed into four BnBr functions by the same treatment with MesSiCl/LiBr, and this resulted in a chain-end-(BnBr)4-functionalized PS. As the coupling and transformation reactions proceeded both cleanly and quantitatively, the same reaction sequence could be repeated four more times to successfiiUy introduce 8,16, 32, and 64 BnBr functions at the chain-ends (Scheme 5.19 Table 5.3) [184]. Furthermore, the same reaction sequence could be carried out with a-(BnBr)2-functionalized PMMA to afford a series of weU-defined chain-end-BnBr-multi-functionalized PMMAs with up to 16 BnBr functions [185]. 

Hirao A, Hayashi M, Loykulnant S, Sugiyama K. Precise syntheses of chain-multi-functionalized polymers, star-branched polymers, star-linear block polymers, densely... 

There are now a number of techniques which may be used to prepare elastomeric networks of known structure Q-8). Two particularly useful and convenient ones involve the multi-functional end-linking of hydroxyl-terminated (4-16) or vinyl-terminated polydimethylsiloxane (PDMS) chains (3,17-21), and the cross-linking of PDMS chains through vinyl side groups present in known amounts and in known locations along the chains (4,18,22-25). A typical reaction of this type is... 

Tew GN, Aamer KA, Shunmugam R. Incorporation of terpyridine into the side chain of copolymers to create multi-functional materials. Polymer 2005 46 8440-8447. 

Stereocontrolled functionalization of steroidal side chains in nature is closely related to the function of steroids in living organisms. The regio- and stereochemistry of functional groups exert strong influence on the biological activities of steroids. Due to their multi-functional nature, the homoenolates provide an effective tool for synthetic efforts in this field. 

Scheme 12 Mode of action of multi-functional acrylates in improving the grafting efficiency, through branching of grafted substrate chains...

Most of these polymers have multi-functional character, which results in cross-linked heterogeneous products. In contrast, monomethoxy polyethylene glycol (PEG) presents only one reactive terminal group per polymer chain. Once PEGy-lated with these compounds, the protein acquires a brush-like shape, with the hydrophilic PEG chains extended from the protein to the solvent. 

An interesting dimension of metal-coordinated self-assembly that is often ignored, or at least not exploited to its fullest extent, occurs when the resulting coordination complex is a charged species and, as such, in need of a counterion. This counterion itself presents yet another subtle instance of ionic self-assembly, which often is overshadowed by its partner, the coordination complex. The second multi-functional side-chain supramolecular polymer system is based on this simple but important concept [14, 106-111]. In 2003, Ikkala and coworkers reported a study in which they exploited (1) a side-chain functionalized polymer, poly(vinyl-pyridine), (2) metal-coordination self-assembly via a tridentate Zn2+ complex and (3) ionic self-assembly through functionalized counterions, i.e. dodecylbenzene-sulfonate ions, to form multiple self-assembled complexes which adopted a cylindrical morphology (Fig. 7.23) [112]. 

If the effect of co-agents on crosslinking efficiency is just the suppression of macroradical side reactions, such as chain scission and disproportionation, one should expect monofunctional co-agents to be as effective as their multi-functional analogues (if compared at the same molar level of unsaturation). This is definitely not the case, as will be demonstrated. 

The formation of such multiply coordinated surface intermediates would be expected to be enhanced by adsorption of multi-functional reagents, e.g., oxygenates with hydrocarbon chains more reactive than saturated alkyl ligands. To test this hypothesis, we have also examined the adsorption and reaction of allyl alcohol (CH2=CH-CH20H) and acrolein (CH2=CH-CHO) on the Rh(lll) surface. While these molecules do exhibit evidence for interaction with the surface via both their oxygen and vinyl functions, and while they appear to preserve the divergence of decarbonylation pathways observed for their aliphatic counterparts, their reactivity patterns add yet another layer of complexity to the puzzle of oxygenate decarbonylation. 

Dextrins are hydrolyzed by a membrane-bound enzyme isomaltase, which occurs in the same polypeptide chain as sucrase, the enzyme that hydrolyzes sucrose, Two active sites (catalytic sites) reside on one polypeptide chain. The entire protein is called sucrase-isomaltase. Enzymes containing more than one active site on one polypeptide chain are called multi functional. The orientation of sucrase-isomaltase in the gut cell, or enterocyte, is shown in Figure 2.43. Both active sites are situated in the lumen of the gut the N-terminal region is anchored in the membrane. Each of the active sites of sucrase-isomaltase is capable of hydrolyzing maltose. Perhaps a better, although cumbersome, name for the enzyme would be sucrase/maltase-isomaltase/maliase. The isomaltase catalytic site is closest to the membrane, whereas the sucrasc site is the C-terminal portion of the enzyme. 

The synthesis of a miktoarm star copolymer of the type AnBn has been also demonstrated. The synthesis was performed via ATRP using divinylbenzene, as the core cross-liking agent. PEO macroinitiator chains were utilized for the polymerization of divinylbenzene forming a star polymer, with a random number of branches. The above star polymer was used as a multi-functional initiator for the polymerization of methacrylate monomers. Therefore, the synthesis of an amphiphilic miktoarm star copolymer was realized [54]. Finally, the hydrolysis of the protected methacrylate block led to the preparation of the desired DHBCs, namely the PEOn-PMAA stars. SEC analysis of the preeursor PEOn-PMMA copolymer revealed a relatively broad molecular weight distribution. Nevertheless, this is a good example for the synthesis of A Bn double hydrophilic star copolymers. 

The reaction between these three components leads to the formation of segmented copolymers characterised by the alternation of hard and soft segments. Hard segments are based on blocks formed by reaction of the di- or multi-functional isocyanate with the chain extender, while the polyol-based units form the soft segments. As a result of the thermodynamic incompatibility between hard and soft segments, PURs are characterised by a biphasic morphology (GunatiUake et al., 2011) (Fig. 6.2). 

The photoinduced addition of a thiol (RSH) to an olefinic double bond has been used to produce polymer networks by taking multi-functional monomers [37-44]. The thiol-ene polymerisation proceeds by a step growth addition mechanism which is propagated by a free radical, chain transfer reaction involving the thiyl radical (RS ). The initial thiyl radicals can be readily generated by UV-irradiation of a thiol in the presence of a radical-type photoinitiator. The overall reaction process can be schematically represented as follows ... 

Multi-functionalized Polyimides. As shown in Scheme 3, the polyimides containing pendant N-acylated caprolactam moieties were prepared by the two-step polycondensation of BAPBC with commercial dianhydrides. A polyamic acid (PAA) viscous solution was formed by stirring equimolar amounts of the derivatized diamine with the dianhydride in NMP at room temperature. The subsequent chemical imidization was carried out by adding pyridine and acetic anhydride to the PAA solution to produce the multi-functional polyimide. The amount of pendant groups incorporated and the rigidity of the polyimide chains were varied by copolymerizations with non-derivatized diamines such as o-tolidine (OTOL), m-tolidine (MTOL), or 2,2 -bis(trifluoro methyl)benzidine (PFMB). The incorporation of the N-acylated caprolactam moieties in the polyimide chains was confirmed by the FTIR absorptions at 2931 and 2864 cm (Uas and CH2 in pendant acylated caprolactam moieties) as well as the absorptions at 1778 and 1727 cm (v s and Vg, C=0 in imide ring). 

In the following we will outUne two basic methods to synthesize LC side chain elastomers. As a starting point for the synthesis of LC elastomers a mixture of mesogenic monomers and bi- or multi-functional crossUnker molecules may serve. This will be discussed in the first part of the section. Alternatively, polymer analogous reactions, where the mesogenic moieties are attached to a polymer backbone, can be employed, which will be discussed in the second part of the section. 

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