Influence of ortho-substituents on the synthesis and properties of poly(phenylacetylene)s

The phenylacetylene derivatives (4‐decyloxyphenyl)acetylene (M1), (4‐decyloxy‐2‐methylphenyl)acetylene (M2), and (4‐decyloxy‐2,6‐dimethylphenyl)acetylene (M3) were polymerized by the well‐defined Schrock‐type initiator Mo[N‐2,6‐i‐Pr2C6H3)(CHCMe2Ph)[OCMe(CF3)2]2 (I1) and by the ill‐defined quaternary system MoOCl4–n‐Bu4Sn–EtOH–quinuclidine (1:1:2:1) (I2). Comparison of the compatibility of the initiators with the different monomers revealed a correlation of the size of the ortho‐substituents and the polymerizability of the monomers. M1 and M2 readily polymerized employing I1, but conversion of the sterically demanding monomer M3 remained incomplete. However, the use of I2 led to high monomer conversions and polymer yields only in case of M2 and M3. The steric bulkiness of the ortho‐substituents also decisively affected the maximum effective conjugation length (Neff) of the polymers and hence their absorption maximum (λmax) as well as their solution stability as shown by UV–vis and GPC studies, respectively. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4466–4477, 2004 A series of poly(phenylacetylene)s bearing increasingly sterically demanding ortho‐substituents in their phenyl rings were prepared via polymerization initiated either by Mo[N‐2,6‐i‐Pr2C6H3)(CHCMe2Ph)[OCMe(CF3)2]2 or by the quaternary system MoOCl4–n‐Bu4Sn–EtOH–quinuclidine (1:1:2:1). Depending on the steric demands of the ortho‐substituents of the monomer and the initiating system employed, the synthesis of soluble, deeply colored poly(phenylacetylene)s was achieved in moderate to high yields. The size of the ortho‐substituents decisively influenced not only the polymerizability of the monomer with the initiator used, but also the maximum effective conjugation length of the polymers as well as their solution stability.