Aromatization, polymer-analogous

We are able to functionalize our polyphenylene dendrimers via three different methods the use of functionalized cyclopentadienones, polymer-analogous reactions (group conversions), and electrophilic aromatic substitution. 

Both theoretical and experimental studies show that not only are aromatic ladder polymers more thermally stable but they are also more highly conducting than analogously structured nonladder systems.In this communication, we report the synthesis and electronic properties of a ladder aromatic polymer, poly(8-methyl, 2.3-6,7-quinolino) (PMQ). The experimental procedures for preparation and characterization of PMQ are described in refs. 5 and 6. 

A potentially valuable characteristic of poly(ether-ketone-carborane)s is that they display enormously enhanced char-yields (up to 95% on pyrolysis in air), compared to the yields obtained from analogous all-aromatic polymers.7 This behaviour suggests that carborane-based polyketones such as 7 could eventually find application as fire-retardants and as precursor polymers for carbon-ceramic materials. 

Aromatization experiments show some evidence for relatively small aromatic substructures (naphthalene, anthracene, tetracene) and this independently demonstrates the success of the polymer-analogous cyclization process. The occurence of up to 20% non-cyclized vinylic side-groups is an indication of the statistical nature of the ring-closure reaction [58]. 

The next two approaches for synthesizing structurally defined ladder-type oligomers and polymers, discussed in sects. 4.3. and 4.4., rest on the formation of the single-stranded intermediates via polycondensation of (aromatic) monomers, again followed by a polymer-analogous ring-closure sequence. 

Preparation and characterization of highly branched aromatic polymers, polyphenylenes, polyesters, polyethers, and polyamides, were reviewed. These polymers were prepared from condensation of AB -type monomers, which gave noncrosslinked, highly branched polymers. The polymer properties are vastly different compared to their linear analogs due to their resistance to chain entanglement and crystallization. 

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. 

Aramids The term aramid is used to describe aromatic and partially aromatic polyamides, which constitute a class of materials that are analogous to the aliphatic nylons . The fully aromatic polymers in this category are linear, but not thermoplastic, as they decompose before they flow sufficiently to allow shaping. However, wet spinning of fibres is possible and such materials have many technical applications besides being used as reinforcement. 

Over the last decade, several new proton exchange membranes have been developed. The new polymers in fuel cell applications are based mostly on hydrocarbon structures for the polymer backbone. Poly(styrene sulfonic acid) is a basic material in this field. In practice, poly(styrene sulfonic acid) and the analogous polymers such as phenol sulfonic acid resin and poly(trifluorostyrene sulfonic acid), were frequently used as polymer electrolytes for PEMFCs in the 1960s. Chemically and thermally stable aromatic polymers such as poly(styrene) [ 3 ], poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbony 1-1,4-phenylene) (PEEK) [4], poly(phenylenesulfide) [5], poly(l,4-phenylene) [6, 7], poly (oxy-1,4-phe-nylene) [8], and other aromatic polymers [9-11], can be employed as the polymer backbone for proton conducting polymers. These chemical structures are illustrated in Fig. 6.2. 

The target of the polymer-analogous aromatization is then the conversion (dehydrogenation) of the saturated carbon centers still present. For this purpose, Schliiter et al. used DDQ as oxidant, in somewhat more than equimolar amounts. The course of the reaction can be followed by an increase in color from yellow-orange to... 

Tan et al. investigated polymers made from bis-benzocyclobutenes [13-15]. As the benzocyclobutane is analogous to tbe dien, tbe Diels-Alder addition takes place. This reaction is applied to the preparation of polyimides. The advantage of this system is that the resultant polymer is oxidized to form thermally stable aromatic polyimides (Fig. 7). 

An alternative approach utilizes polymeric analogs of PBD. The oxadiazole unit may be in the polymer main chain or attached as a side chain. A reasonable device performance has been demonstrated in poly(aromatic oxadia/ole)s [71—74. ... 

There have been a number of different synthetic approaches to substituted PTV derivatives proposed in the last decade. Almost all focus on the aromatic ring as the site for substitution. Some effort has been made to apply the traditional base-catalyzed dehydrohalogenation route to PTV and its substituted analogs. The methodology, however, is not as successful for PTV as it is for PPV and its derivatives because of the great tendency for the poly(u-chloro thiophene) precursor spontaneously to eliminate at room temperature. Swager and co-workers attempted this route to synthesize a PTV derivative substituted with a crown ether with potential applications as a sensory material (Scheme 1-26) [123]. The synthesis employs a Fager condensation [124] in its initial step to yield diol 78. Treatment with a ditosylate yields a crown ether-functionalized thiophene diester 79. This may be elaborated to dichloride 81, but pure material could not be isolated and the dichloride monomer had to be polymerized in situ. The polymer isolated... 

All the derivatives examined above owe their instability to the presence of the furan ring similar aldehydes, carbinols, chlorides, etc. bearing aliphatic and aromatic substituents are not prone to resinify. An analogous singularity of behaviour is encountered in furan polymers, as underlined at the beginning of this chapter. In a polymer prepared from a furan derivative three different situations must be considered ... 

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