Recently, dendrimers have attracted much attention as the macromolecules with precisely defined threedimensional structure in organic and polymer chemistry. 1 In particular, stiff dendrimers are expected as ideal model systems for studying how physical properties depend on molecular size and architecture because the stiff dendrimers have shape persistency in comparison with flexible dendrimers. 2 The shapes of dendrimers should be significantly affected by the core group structures. Most of the synthesized dendrimers were spherical or globular, except for a few examples, 3,4 and usually showed a low viscosity, which was unfavorable for bulk materials with molding and film-forming ability. If we use a linear molecule for the core group instead of a small spot molecule, a cylindrical or rodlike macromolecule with uniform diameter will be yielded, preserving the advantage of dendrimers such as welldefined dendritic structure with many functional groups localized on the periphery of the dendrimer. For the extension of the convergent approach, the cylindrical or rodlike dendrimer should be synthesized by polymerization of a polymerizable group attached to the focal point of the monodendron, and some synthetic efforts including copolymerization were attempted by some research groups. 4 The polydendrons with a high molecular weight would also have other properties, such as membrane-forming ability, that lead to application for highly selective membranes, and the well-defined dendritic and cylindrical structure is expected to play an important role on the permselectivity.Substituted polyacetylenes can be synthesized stereoselectively by an appropriate polymerization catalyst 5,6 and have attracted attention as one of the most interesting functional polymers with electrical conductivity, 7 nonlinear optical 8 and magnetic properties, 9 and gas-selective 10 or enantioselective 11 permeability as their membrane properties. Therefore, we selected poly-(phenylacetylene) for the central core molecule and synthesized polydendrons by the polymerization of monodendrons with the phenyleneethynylene repeating unit.The monodendrons 12 were synthesized as shown in Scheme 1 by repetition of the coupling reaction of 3,5-dibromo-1-(3-hydroxy-3-methylbutynyl)benzene with the phenylacetylene derivatives of an earlier generation and the elimination reaction of a terminal acetylene-protecting group according to a modified literature procedure, 2 where (3,5-di-tert-butylphenyl)acetylene (DB0H) or [4-(trimethylsilyl)phenyl]acetylene (TMS0H) was used as the starting peripheral group to afford adequate solvent solubility. The monodendrons were polymerized with a rhodium catalyst, [Rh(C 7 H 8 )Cl] 2 , and the polymerization mixtures were purified by precipitating the chloroform solution into methanol or methanol/benzene (3/2) to yield the polydendrons 13 as yellow powders (Table 1). The rhodium catalyst has been reported to be effective for the polymerization of monosubstituted acetylenes and ineffective for disubstituted acetylenes. 6 The m...

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Phenyleneethynylene macrocycle‐substituted acetylenes were synthesized by repetition of the Sonogashira coupling reaction, and the elimination reaction of the terminal acetylene protecting group. The monomers were polymerized with a rhodium catalyst, [Rh(nbd)Cl]2, at the terminal acetylene unit, and the polymerization mixtures were purified by precipitating into methanol to yield the corresponding poly(phenylacetylene) derivatives as yellow‐red powders, which had a high degree of polymerization ($\overline {DP}$ ≈ 500) in spite of their steric bulkiness. The trimethylsilyl and pentamethyldisiloxanyl groups of polymers improved their solubility, and the polymers were soluble in common organic solvents, such as toluene, chloroform and tetrahydrofuran.magnified image

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