Semi-ladder polymers

Although there seem to be no true ladder polymers in large-scale commercial production, several semi-ladder polymers that have rather rigid structures are employed where high-temperature strength is important. Among these are... 

BPA/DC was compounded with high-temperature resistant ladder and semi-ladder polymers. A composition, which contained BPA/DC, a polyimide resin, organic Zn salt and benzyldimethylamine in A -methylpyrrolidone solution was described. The binder was destined for the manufacture of copper clad laminates. Tg of the cross-linked material was 265 °C [50]. Another example is a binder obtained from BPA/DC and polyphenylquinoxaline in chloroform [51]. 

A great part of the work on the BIC unit has been done for developing precursors to ladder or semi-ladder polymers. Two different ways have been used so far, the direct synthesis of the BIC unit and the polymerization of this unit or the polymerization of 3,6-dibenzoyl-substituted carbazole and a ring-closure afterward. This last pathway affords a completely ladder-type polymer which is of great interest for various applications. 

To the best of our knowledge, there is only one paper by Mullen et al. [ 125] that presents the polymerization of the BIC unit. The semi-ladder polymer was synthesized by a nickel(0)-mediated Yamamoto-type polymerization using dichlorobisindenocarbazole or dibromobisindenocarbazole as precursors. The two polymers were synthesized in good yields (77 and 70%). They both show a strong blue emission in solution with a maximum centered at 445 nm. 

Moreover, semi-ladder polymers based on DIC units were obtained in much more classical ways. 2,11- and 3,10-dichloro DIC derivatives were polymerized through a nickel(0)-mediated Yamamoto polymerization reaction [95]. The resulting polymers are soluble in ODCB and partially soluble in CB. The absorption maxima of the BIC-based polymers clearly indicate a planar structure. The absorption maxima of the polymeric precursors show a primary maximum around 350 nm compared to the ladder-type polymers where the maximum is centered around 470 nm [50]. This significant red shift clearly indicates the higher degree of conjugation in the planar rigid polymers. The fluorescence spectra of those polymers also show the same trend. 

Table 3.5 presents a selection of values of various conjugated polymers, determined by THG measurements, while Table 3.6 shows values of some full-ladder and semi-ladder polymers, determined by means of the DFWM technique. 

C. M. Zimmerman, W. J. Koros, Comparison of gas and sorption in the ladder polymer BBL and some semi-ladder polymers. Polymer, 40, 5655 (1999). 

The polymers highlighted in this chapter include those based on polyazoles, polybenzazoles, aromatic polyimides, and a variety of ladder and semi-ladder polymers. The key synthetic strategies to produce these polymers as well as detailed assessment of various synthetic strategies are described in detail. Molecular composites, in which molecular-level blends of rigid rod polymers are produced to enhance strength, are described. 

Some metals form coordination polymers with sulfur that have a semi-ladder structure. One series are the bisdithiocarbamate polymers, which have the typical structure shown... 

By varying the heating rate, cyclodehydration takes place, giving either a semi-ladder or ladder structure. The semi-ladder polybenzimidazolone is soluble in some solvents. The ladder polymer subsequently formed is insoluble. This type of polymer is stable to 450—650°C in nitrogen. 

An alternative to a linear polymer is a branched one. The branches can be long or short. Low-density polyethylene, for instance, can have both short and long branches. Linear and branched molecules are shown in Fig. 1.1a, b. Branched polymers can also be star- or comb-shaped (Fig. 1.1c, d). In addition to the above, polymer molecules can also be double-stranded. Such polymers are called ladder polymers (Fig. Lie). It is also possible for polymers to have semi-ladder structures (Fig. l.lf). 

Polybonding should be utilized as much as possible. The polybonding concept leads to the utilization of semi-ladder or ladder polymers in which each skeletal atom is linked in the polymer chain by more than one bond, so that the chain cannot be broken by the rupture of a single bond. 

Heteroaromatic Ladder Polymers. BBB and BBL are benzimidazophenan-throline ladder poljuners which lend themselves to third-order NLOs through their planar conformation, quasi-two-dimensional structure, and to end use applications through their mechanical and thermal stability and electrical properties (252). BBL and BBB are very similar in their repeat imit structure the manner in which the monomer units are linked together, however, is different. BBL (10) has a full-ladder structure, which means that the monomeric imits are linked by two covalent bonds, whereas BBB (11) has a semi ladder structure because its... 

The most promising applications of template polymerization seems to be the production of materials in which the daughter polymer and the template together form a final product, because the synthesis of polymers requiring further separation of the product from the template is not acceptable for industry. The template process can be applied in order to produce a set of new materials on the basis of ladder-type polymers, semi-adder copolymers, the properties of which are not yet well known. 

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