Ladder polymer synthesis

Ladder polymer, synthesis of, 503 Lanthanide catalysts, 288 Lanthanide compounds, 73 Latent-reactive polymers, 455 Laurolactam, 136... 

The synthetic route represents a classical ladder polymer synthesis a suitably substituted, open-chain precursor polymer is cyclized to a band structure in a polymer-analogous fashion. The first step here, formation of the polymeric, open-chain precursor structure, is AA-type coupling of a 2,5-dibromo-1,4-dibenzoyl-benzene derivative, by a Yamamoto-type aryl-aryl coupling. The reagent employed for dehalogenation, the nickel(0)/l,5-cyclooctadiene complex (Ni(COD)2), was used in stoichiometric amounts with co-reagents (2,2 -bipyridine and 1,5-cyclooctadiene), in dimethylacetamide or dimethylformamide as solvent. 

Nevertheless, the route is attractive, because many interesting ladder structures are not accessible using the polycondensation or polyaddition of multifunctional monomers [2, 5]. Besides the specific problems of ladder polymer synthesis discussed above, another problem is almost invariably associated with... 

A new quality in ladder polymer synthesis via multifunctional polycondensation was reached in the late 1960s when poly(benzimidazobenzo-phenanthroline) (BBL) 12 was prepared by Arnold and van Deusen [21 -24]. The polymer was synthesized from naphthalene-l,4,5,8-tetracarboxylic acid dianhydride (11) and 1,2,4,5-tetraaminobenzene (la) in strong acidic media (polyphosphoric acid, sulfuric acid). BBL is completely soluble in concentratal sulfuric acid or methanesulfonic add and is processible into durable films and... 

It is clear, however, that such physical aspects are intimately related to the quality of ladder polymer synthesis, which is evidenced by such facts as structural homogeneity and solubility of the resulting products. 

Discussion of ladder polymers also enables us to introduce a step-growth polymerization that deviates from the simple condensation reactions which we have described almost exclusively in this chapter. The Diels-Alder reaction is widely used in the synthesis of both ladder and semiladder polymers. In general, the Diels-Alder reaction occurs between a diene [XVI] and a dienophile [XVll] and yields an adduct with a ring structure [XVlll] ... 

In Figure 8-1 we show the chemical structure of m-LPPP. The increase in conjugation and the reduction of geometrical defects was the main motivation to incorporate a poly(/ -phenylene)(PPP) backbone into a ladder polymer structure [21]. Due to the side groups attached to the PPP main chain excellent solubility in nonpolar solvents is achieved. This is the prerequisite for producing polymer films of high optical quality. A detailed presentation of the synthesis, sample preparation,... 

The preferred catalysts are salts of inorganic and organic acids as well as tertiary amines. Phthalic anhydride, succinic anhydride and maleic anhydride are typical acid anhydrides, while ethylene oxide, propylene oxide, epichlorohydrin and phenyl glycidyl ether are typical epoxides. The synthesis of a ladder polymer was carried out by using bisanhydrides264. ... 

This idea was realized impressively in 1991 with the first synthesis of a soluble, conjugated ladder polymer of the PPP-type [41]. This PPP ladder polymer, LPPP 26, was prepared according to a so-called classical route, in which an open-chain, single-stranded precursor polymer was closed to give a double-stranded ladder polymer. The synthetic potential of the so-called classical multi-step sequence has been in doubt for a long time in the 1980s synchronous routes were strongly favoured as preparative method for ladder polymers. 

In 1993, Scherf and Chmil described the first synthesis of a ladder-type poly(pflra-phenylene-czs-vinylene) (116) [138]. On the one hand, ladder polymer 116 represents, a planar poly(phenylene) containing additional vinylene bridges on the other hand, it is a poly(phenylenevinylene) with aryl-aryl linkages in the polymeric main chain. The target macromolecules, as fully aromatic ladder polymers, are composed of all-carbon six-membered rings in the double-stranded main chain (an example of angularly annelated poly(acene)s). 

In the field of polymer chemistry the regio- and stereoselectivity of the Diels-Alder reaction is used for the concerted synthesis of structurally homogeneous double-stranded ladder polymers [39], which are useful materials with nonlinear optical properties and high electrical conductivity. It has turned out that the repeated Diels-Alder method is superior to an alternative two-step process, in which first an open chain precursor is formed followed by polymer ring closure as structural defects can occur [40]. 

The synthesis of fully conjugated semiconducting para-phenylene ladder polymers by microwave-assisted palladium-mediated double Suzuki and Stille-type reactions has been demonstrated by Scherf and coworkers (Scheme 6.27) [58], The procedure, which yields polymeric material in ca. 10 min, has no adverse effects on the quality of the polymers and displays a high degree of reproducibility. Compared... 

Scherf, U. and Mullen, KThe Synthesis of Ladder Polymers. Vol. 123, pp. 1-40. 

Another approach to CPL is the synthesis of conjugated polymers with intrinsic chiro-optical properties. A variety of polymers with CPPL have been synthesized so far. Most of them are based upon well-known conjugated polymers such as poly(thiophene)s [4,111], polyphenylene vinylene)s [123], poly(thienylene vinylene)s [124], ladder polymers [125], PPPs [126], polyphenylene ethynylene)s, [127] and poly(fluorenes) [128]. All of them have been modified with chiral side-chains, which induce the chiro-optical properties. 

Figure 14.9. Synthesis of perfluoro nitrogen-containing ladder polymers.

Note The souree-based name identifies the starting monomer of this ladder polymer, the synthesis of which comprises a multistep reaction involving condensation and cyclization. 

Polymers such as PBI have a weak link in them since a single covalent bond connects the phenyl rings in biphenyl. This weakness is overcome by the synthesis of ladder polymers, such as polyquinoxaline structures 4.64 and 4.65, and polydithione (structure 4.66), which have two covalent bonds throughout the chain. Thus, the integrity of the polymer is maintained even if one bond is broken ... 

The Diels Alder reaction, involving the [4 + 2]-cycloaddition of an unsaturated group (di-enophile) to a 1,3-diene, has been studied for the synthesis of ladder polymers, such as the reaction of 2-vinyl-l,3-butadiene with benzoquinone [Bailey, 1972] (Eq. 2-247). Related polymerizations are those utilizing the [2 + 2]-cycloaddition reaction [Dilling, 1983]. While [4 + 2]-cycloaddition reactions are thermally induced, [2 + 2]-cycloaddition reactions are... 

Another example is a synthesis of a ladder polymer suggested by Bamford and... 

Research Focus Synthesis of silsesquioxane ladder polymers effective as iniferters containing polymerizable grafted components. 

Attention was then turned to aromatic heterocyclic ladder polymers other than BBL. Due to the complexities in their synthesis, ladder polymers were not reported extensively in the literature at that time. A sample of polyfluoflavine (I) having an inherent viscosity in methanesulfonic acid of 2.5 was obtained from professor C. S. Marvel at the University of Arizona. The ladder polymer was prepared [5] from the A-B polycondensation of 2,3-dihydroxy-6,7-diamino-quinoxaline hydrochloride in PPA. Transparent blue sheets were observed on precipitation of this polymer from methanesulfonic acid, and when collected and dried, it formed gold films much like the color of the BBL films. It was felt at that time that all ladder polymers of sufficient molecular weight would form precipitated films. 

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