Polymer ladder

Lastly, we consider a class of compounds called ladder polymers, which are made up of a double-stranded backbone that is linked at regular intervals into rings so that the schematic structure is... 

Spiro polymers are also sometimes classified as ladder polymers, and molecules in which the ladder structure is interrupted by periodic single bonds are called semiladders. Consisting entirely of fused ring structures, ladder polymers possess very rigid chains with excellent thermal stability. 

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] ... 

The first ladder polymer with a high degree of structural perfection was reported in 1960 and was prepared by the equilibrium condensation of phenyltrichlorosilane Figure 29.19). 

Using a mononuclear tetramine a polycondensation very similar to that used with BBB can occur which leads to a ladder polymer of high structural perfection (BBL) Figure 29.20). 

Polyfunctional condensation has also been used to prepare ladder polymers from, for example, the following other intermediates ... 

Related to the ladder polymers are the spiro polymers as typified by the reaction product of cyclo-octadecane-1, 10-dione with pentaerythritol Figure 29.22). 

The commercial fibers are produced from rayon, polyacrylonitrile, and petroleum pitch. When acrylonitrile is heated in air at moderate temperatures (= 220°C ), HCN is lost, and a ladder polymer is thought to be the intermediate ... 

The softening behaviour of a thermoplastic material depends to a large extent on the flexibility of the chain and the ability to crystallise. Significant cross-linking of a reasonably stiff-chained polymer will lead to material that is unlikely to soften below its decomposition temperature. Intermediate to the linear and cross-linked polymers are various ladder polymers in which the polymer molecule consists of a pair of more-or-less parallel chains bridged in a manner analogous to the rungs of a ladder. 

Photophysics of Methyl-Substituted PPP-Type Ladder Polymers... 

Concerning the nature of electronic traps for this class of ladder polymers, we would like to recall the experimental facts. On comparing the results of LPPP to those of poly(para-phenylene vinylene) (PPV) [38] it must be noted that the appearance of the maximum current at 167 K, for heating rates between 0.06 K/s and 0.25 K/s, can be attributed to monomolecular kinetics with non-retrapping traps [26]. In PPV the density of trap states is evaluated on the basis of a multiple trapping model [38], leading to a trap density which is comparable to the density of monomer units and very low mobilities of 10-8 cm2 V-1 s l. These values for PPV have to be compared to trap densities of 0.0002 and 0.00003 traps per monomer unit in the LPPP. As a consequence of the low trap densities, high mobility values of 0.1 cm2 V-1 s-1 for the LPPPs are obtained [39]. 

The resulting ladder polymer LPPP 12 possesses a number average molecular weight of 25000, which corresponds to the incorporation of 65 phenylene units. No structure defects could be detected using NMR spectroscopy. LPPP 12 is... 

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,... 

T. Pauck, R. Hennig, M. Pcnter, U. Lemmer, U. Siegncr, R. F. Malm, U. Scherf, K. Mullen, H. Bassler, E.O. Gobel, Femtosecond dynamics of stimulated emission and photoinduced absorption in a PPP-typc ladder polymer Client. Phys. Lett. 1995, 244, 171. 

W. Graupner, G. Leising. G. Lanzani, M. Nisoli. S. De Silvcstri, U. Scherf, Femtosecond relaxation of pholoexcilalions in a poly(para-pheuy (cueHype ladder polymer Phys. Rev Lett. 1996, 76, 847. 

This compound has been investigated by several groups,379- 384 but due to its practical insolubility it has not been fully characterized. Another approach to obtain phthalocyanine network polymers is with the use of crown ethers385 or other groups like di oxy -para-p h enyle n e3 8 6 as bridging units between the macrocycles. Some attempts to obtain metal phthalocyanine substructures arranged as ladder polymers have also been proposed (see below).344... 

Phthalocyanines with side groups which can undergo Diels-Alder reactions can be synthesized as precursors for ladder polymers (see pp772, 773).344-345 For these kinds of compounds an intrinsic conductivity is predicted.346 Both dienophilic and enophilic phthalocyanines have been prepared. The possibility to undergo a Diels-Alder reaction was tested with fumaronitrile and 2,3-dimethylbutadiene.345 Via a Diels-Alder reaction, a connection between a phthalocyanine and [60]fullercne was also achieved.336... 

Polydithiazoles Polyoxadiazoles Polyamidines Pyrolyzed polyacrylonitrile Polyvinyl isocyanate ladder polymer Polyamide-imide Polysulfone Decompose at 525°C (977°F) soluble in concentrated sulfuric acid. Decompose at 450-500°C (842-932°F) can be made into fiber or film. Stable to oxidation up to 500°C (932°F) can make flexible elastomer. Stable above 900°C (1625°F) fiber resists abrasion with low tenacity. Soluble polymer that decomposes at 385°C (725°F) prepolymer melts above 405° C (76l.°F). Service temperatures up to 288° C (550°F) amenable to fabrication. Thermoplastic use temperature —102°C (—152°F) to greater than 150° C (302°F) acid and base resistant. 

Phosphonitrilic Metal polyphosphinates Phenylsilesesquioxanes (phenyl-T ladder polymers)... 

Polyvinyl isocyanate ladder polymer Polyamide-imide Soluble polymer that decomposes at 385°C (725°F) prepolymer melts above 405°C (761°F). Service temperatures up to 288°C (550°F) amenable to fabrication. 

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