| Popis: |
2-, 3- and 4-Iodophenylacetylenes (IPA) have been polymerized with [Rh(cod)(OCH3)]2 complex in THF (system Rh), MoCl5 in benzene (Mo), WOCl4 in benzene (WB) and WOCl4/Ph4Sn in benzene-dioxane 1 : 1 (WD). All the systems provide poly(iodophenylacetylene)s (PIPA) and diverse amounts of oligomers (mostly cyclic trimers and tetramers) but the system 2-IPA/Rh that provides mostly dimers only. 2-IPA has also been polymerized with MoOCl4/Bu4Sn/EtOH in toluene (Masuda's catalyst system), however, neither living nor pseudo-living polymerization has been observed. The ring-iodine steric effects control the polymerization activity of the Rh and WB systems and the oligomerization activity of the Mo system. The ring-iodine electronic effects are important for the oligomerization activity of the Rh and WB systems and both oligomerization and polymerization activity of the WD system. Both types of the ring-iodine effect are important for polymerization activity of the Mo system. Rh catalyst provides high-cis-transoid, head-to-tail (HT) 3-PIPA that slowly isomerizes in CDCl3 solution to an insoluble trans-polymer. In the case of 4-PIPA, the isomerization is extremely fast upon polymer entering into contact with methanol. On the basis of spectral changes accompanying this isomerization, the Raman band at 1 338 cm-1 is assigned to the presence of HT sequences of both cis-transoid and trans-cisoid type. The other catalysts provide irregular PIPAs with content of both cis units and HT sequences decreasing in order Mo > WD > WB. Solubility of PIPA samples is shown as a result of complex interplay of the ring-iodine position and the polymer microstructure and molecular weight. |
