Macrocyclic ring-containing polymers

Synthesis of Macrocyclic Ring-Containing Polymers Via Cyclopolymerization and Cyclocopolymerization... 

The principle of cyclopolymerization has been applied to the synthesis of macrocyclic ether-containing polymers which may simulate the properties of crown ethers. l,2-Bis(ethenyloxy)benzene (a 1,7-diene) and l,2-bis(2-ethenyloxyethoxy)benzene (a 1,13-diene) are typical of the monomers synthesized. Homopolymerization of the 1,7-diene via radical and cationic initiation led to cyclopolymers of different ring sizes homopolymerization of the 1,13-diene led to cyclic polymer only via cationic initiation. Both monomer types were copolymerized with maleic anhydride to yield predominantly alternating copolymers having macro-cyclic ether-containing rings in the polymer backbone. 

Compounds such as [n-Bu2Sn( a-0H)(03SC6H3-2,5-Me2)]2 K are two-dimensional polymers. This compound contains a [Sn2( J.-OH)2] unit as its repeat unit. Such four-membered distannoxanes are linked to each other by an anisobidentate coordination action of the sulfonate ligand to afford a 20-membered macrocyclic ring. The macrocyclic rings, in turn, are linked to each other to afford a coordination polymer (Figure 2.4.15). 

Two-dimensional and three-dimensional structures containing analogous and related macrocyclic ring systems are known for most of the ligand types that form discrete macrocyles. Additionally, there are a few examples for two-dimensional and three-dimensional coordination polymers containing sulfate, phosphate, vanadate, chromate, molybdate, and tungstate, indicating that these are also possible candidates for the formation of discrete macrocycles. 

An interesting polymer containing macrocyclic rings was formed from pyromellitic tetranitrile by condensation with dianilino ether ... 

The circuits discussed hitherto in this section are all in the growing or final tree. Because of the fractal nature of these trees and chemical nomenclature, we shall refer to thejm below as intrafractal rings or intrafractal macrocyclic structures. These should not be confused with interfractal rings or interfractal macrocycles. The latter are formed between fractal polymers as they aggregate to create the network, and each such macrocycle may contain several segments belonging to two or more FPs. Thus, in the final network the number of interfractal macrocyclic structures increases with network perfection and with concentration above CJ. 

An interesting development in monomer synthesis and subsequent polymerization was disclosed earlier this year [51. A synthetic route for preparing giant rings containing about 20 to 40 monomer units was devised. These macrocycles could be polymerized directly to high molecular weight polymers (Equation 3). 

Most of the systems described in Chapter 5 contain small- or medium-sized or multinuclear benzenoid and non-benzenoid arenes. In Chapter 6, Hoger gives an overview over the mastery of the synthesis of macro- and megacycles. He shows different approaches towards shape-persistent macrocycles and carefully examines and discusses selected examples that display the advantages and disadvantages of macrocycle synthesis under kinetic and thermodynamic control. The template approach (both supramolecular and covalent) towards functionalized rings is also discussed and introduces a strong motif of supramolecular chemistry, which is much further developed but in a more polymer-oriented topic, in the next chapter. 

For a synthetic polymer chemist the important question is whether the cyclization processes in cationic ring-opening polymerization can be controlled. If the preparation of linear polymer is attempted, then cyclic oligomers are undesirable side products. This is especially important in synthesis of telechelic polymers containing reactive end groups, because macrocycles would be unreactive admixtures. On the other hand, cyclic polymers, if prepared selectively, could be a valuable materials. 

Thus, cationic polymerization of oxiranes is of little synthetic value, if the preparation of linear polymers is attempted. The high tendency for cyclization may be employed, however, for preparation of macrocyclic polyethers (crown ethers). Polymerization of ethylene oxide in the presence of suitable cations (e.g., Na+, K+, Rb +, Cs + ) leads to crown ethers of a given ring size in relatively high yields, due to the template effect [105], Thus, with Rb+ or Cs+ cations, cyclic fraction contained exclusively 18-crown-6. 

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