Polyphenylene analogues

Polyphenylene Analogues. Early work aimed at the development of linked-ring borazine polymers with structures (2-3) has been outlined in a previous review. In particular, it is worth noting that the metathetical reaction of N-lithio pentamethyl borazine with B-chloropentamethyl borazine (eq. 1) led to LiCl metathesis and production of decamethyl-N,B-diborazine.l2 Extensions of this chemistry resulted in formation of a polyborazinyl chains, estimated to contain ten monomer rings, which melted over a broad temperature range. Unfortunately, little follow up on these polymers has been published perhaps because the polymers are not likely to be efficient ceramic precursors due to their expected low char yields and the inclusion of carbon in their ceramic residues. 

Perfluoropolyphenylene shows about the same stability as the unfluori-nated analogues [271]. Perfluoropolyphenylene ethers are less stable than the corresponding polyphenylene ethers [272]. Perfluoropoly-p-phenyl-enesulphide is less stable than p-polyphenylenesulphide in the range 360-440°C [273]. 

Yang, C.D. et al., Poly(2,7-phenanthrylene)s and poly(3,6-phenanthrylene)s as polyphenylene and poly(phenylenevinylene) analogues, Macromolecules 39, 5213-5221, 2006. 

The selenium and tellurium analogues of PPS have also been synthesized and investigated [50]. As prepared, polyphenylene selenide (PPSe) and polyphenylene telluride (PPTe) are insulators with conductivities of less than 10 S m Exposure of PPSe to AsFs results in an insulator-to-conductor transformation, with a maximum conductivity in the range 0.1-1 S m being achieved. The thermal stability of PPSe is similar to that of PPS, while PPTe is decomposed by relatively mild conditions. 

Despite the open structure of the hyperbranched stiff macromolecules, they are rather compact with radius of gyration, Rq, far smaller than that for the linear analogues. The compactness is mirrored in the modest change in solution viscosity upon the addition of more than 1 g Li-carboxylate terminated polyphenylene to 1 ml water [363], and in the brittleness and inability to form films [383] exhibited by these polymers. A similar very modest effect on solution viscosity was previously observed by Aharoni et al [370] on solutions of the highly branched and very compact poly((x,e-L-lysine) molecules prepared by Denkewalter et al. [332]. 

With respect to the mechanism of gas transport, the polyphenylene oxides can be considered as the polymeric analogues of the microporous adsorbents. The intrinsic micropores, inherent in the supermolecular structure of polyphenylene oxides and belonging to the polymers free volume, are suggested to be formed by a continuous network of interconnected intermolecular microcavities. 

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