POLY(2,5-DIALKOXY-P-PHENYLENE)S - SYNTHESIS AND PROPERTIES

The synthesis of poly(2,5-dialkoxy-p-phenylene)s (PPP) by palladium-catalyzed polycondensation of 2,5-dialkoxy-4-bromophenylboronic acids is described. Number-average degrees of polymerization of ca. 30 have been reached at best. The characterization of the polymers by NMR, IR, UV-VIS and fluorescence spectra, data on the bulk structure obtained by X-my methods, melting behavior and thermal stability are reported. PPP's with long alkoxy side chains exhibit a layered phase structure, those with short or branched alkoxy side chains, cylindrical packing. Poly(2,5-dibutoxy-p-phenylene) was prepared with chain lengths 7 less-than-or-equal-to P(n) less-than-or-equal-to 30. The polymer with P(n) of 30 shows thermal transitions in the bulk phase at 182-degrees-C and 227-degrees-C. It forms an anisotropic melt above 227-degrees-C which only starts decomposing if heated above 300-degrees-C. The polymers of shorter chain length show isotropic melts, with the melting point strongly depending on chain length.