Effective Polymer Analogous Reactions

FIGURE 3.26 Concept of the Kumada catalyst transfer polycondensation, dppp, propane-l,3-diylbis(diphenylphosphane) TM, transmetaUation RE, reductive elimination OA, oxidative addition. 

As already indicated in Section 3.1.3, besides chain and step growth polymerizations, new polymer structures can also be achieved by modifying a precursor polymer structure with new functionalities. Even though this is the base for a number of technically important polymers including polyvinyl alcohol and, for example, ion exchange resins, for many years, this method was not considered to be suitable for the reliable large-scale synthesis of well-controlled polymer architectures, mostly because it is very difficult to achieve very high 

FIGURE 3.27 Examples of active esto-s used for efficient polymer analogous reaction toward functional esters or amides (a) 4-nitrophenylester, (b) ALhydroxysuc-cinimide (NHS) ester, and (c) pentafluorophenylesta-. 

In the last decade, the combination of CRP techniques and newly found or reinvented highly effective and selective organic reactions termed as the click chemistry has been demonstrated to be a versatile tool for the specific constmction of novel functional macromolecules [28]. In 2001, Sharpless et al. [29] introduced the term click chemistry with its famous representative, the cycloaddition of azides with alkynes under copper catalysis. He defined a click reaction with a set of criteria The reaction must be modular, wide in scope, give very high yields, generate only inoffensive byproducts that can be removed by nonchromatographic methods, and be stereospecific (but not 

Due to the rather easy accessibility of novel functional polymer materials by click reactions, their potential scope of applications has significantly broadened in the last years. Through the preparation of functional thin polymer films, biohybrids, or self-assembly structures from end group or side chain functionalized polymers and functional block copolymers, applications, for example, as adhesives or additives, but especially also in optoelectronics, biomedicine, drug delivery, biochips, and micro- and nanoelectronics become accessible. 

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PPEs should offer a potent platform for polymer-analogous reactions, and a family of new materials should be accessible by either complexation or cydoaddition via their bridging triple bonds. A difficulty is the relatively low reactivity of the alkyne units in PPEs. Steric shielding by the adjacent alkyl or alkoxy groups, as well as electronic effects, reduce the re-... 

The sulfide moiety of PPS can be oxidized to a sulfoxide group. This effects a higher temperature stability. The oxidation has been performed as a polymer analog reaction using acetic acid and concentrated nitric acid for 24 h at 0-5 °C [30], However, in this process, long reaction times are required, and the attack of the aromatic rings by nitric acid may occur. 

Fig. 18. Flow scheme and interrelations between triads and neighboring triads during a polymer analogous reaction. Reaction influenced by a neighboring group effect extending one monomer unit to either side of the reacting unit. Corresponding rate equations exemplified by the differential equation for the triad AAA...

Mark-Houwink coefficient (slope) and Mark-Houwink K (intercept). Mark-Houwink coefficient, a, is a measure for the structure of the sample in solution, a change of the slope indicates a structure change. A" is a measure of the segmental density and can be used to measure the effect of chemical reactions on the polymer backbone (studying polymer-analogous reactions) [19]. 

Moran et al. have also reported the preparation of hyperbranched ferrocenyl. S7-based polymers (Figure 8.1). The construction of ferrocenyl —silicon polymers 40 and 41 was effected by the reaction of dilithioferrocene-TMEDA with the tetrachlorosilane 35 (see Scheme 8.10) and the Pt-mediated hydrosilylation of l,l -divinylferrocene with tetrasilyl-hydride 38. The 3-dimensional motif exhibited by hyperbranched polymers 40 and 41 is analogous to that depicted by the ferrocenyl — silicon network structures 38,43 42 and 43 (Figure 8.2). 

The inhibitions described above occurred only when the analog and polynucleotide contained complementary bases. These combinations are not the only ones in which the interaction can occur, e.g., affinity methods detect some interaction between the non-complementary poly-9-vinyladenine and polyadenylate Apparently, such complexes are too unstable to affect the enzymatic reactions nevertheless, extensive modification of the analog can increase the stability of the polymer-polynucleotide complex to the point where such a polymer can effectively inhibit the reaction. Thus, omisssion of the amino group from poly-9-vinyladenine leads to poly-9-vinylpurine and the latter polymer inhibits the reverse transcription of polyadenylate and polyuridylate The introduction of a dimethylamino group in place of the amino group of poly-9-vinyladenine abolMies all of its inhibitory effects All these effects can be correlated with the ability of polymers to form complexes with templates. 

Given that some of the solvent becomes an integral part of the final product and participates in the auxiliary electrode reaction, it is more than just a reaction medium. It is a reactant and should be considered as such. The solvent will also have an effect in determining the conformational nature of the polymer. This effect is analogous to that observed with other macromolecules, such as proteins, that can fold in aqueous solution to protect their hydrophobic groups but unfold in more nonpolar solvents to expose the hydrophobic groups. The choice of solvent is critical, and its role should be considered in light of the detailed polymerization mechanism. 

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