Polymers containing aromatic hydrocarbons in the main chain

2 POLYMERS CONTAINING AROMATIC HYDROCARBONS IN THE MAIN CHAIN 

Some of the most important structures are summarized in Table 20. Many of them are commercial products. Their stability is often very good. Representative data are given in Fig. 68. 

Linear p-polyphenylene is thermally stable and crystalline, but brittle, insoluble and infusible. Therefore there has been considerable effort to insert flexible links such as —O—, —CO—, —NH—, O—CO—, —O—CO—O, N2, —S— or S02 without loss of thermal stability. Poly-p-xylylene has a melting point of 400°C and its mechanical properties are good. It is, however, insoluble and cannot be thermoprocessed. If one or more 

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