Synthesis and thermal stability of phosphaphenanthrene-containing polyacetylenes

New thermal stable mono-substituted polyacetylenes (PAT5 and PAT10) containing phosphaphenanthrene as side groups and end-chains of different lengths were studied. 4-Ethynylbenzoyl and 4-alkoxylbenzoyl were first introduced into the 2-(6-oxide-6H-dibenz <c,e> <1,2> oxaphos-phorin-6-yl)-dihydroxyphenylene (ODOPB) through a two-step esterification, respectively, which synthesized the phosphaphenanthrene- containing acetylenic monomers. The polymerization of novel monomers was carried out by using [Rh(nbd)Cl]₂-NEt₃ as the catalyst at room temperature in high yield (> 90%). The structure and optical properties of the polyphenylacetylenes were characterized by means of ¹H-NMR, FT-IR, UV-Vis and photoluminescence spectroscopy, respectively, which showed that the polyacetylenes were synthesized successfully. During the introduction of phosphaphenanthrene as side-groups, PAT5 and PAT10 are yellow-brown and soluble in common solvents. However, The model polyacetylene PA5 in the absence of phosphaphenanthrene is red and insoluble. GPC reveals two peaks for the novel polacetylenes. The first peak is attributed to the aggregation state between polymeric chains (10⁷), and the second one is to the real molecular weight (10⁴). The experimental results indicate that the regular supramolecular structures between phosphaphenanthrene-containing pendent groups are fabricated based on the strong π-π stacking and polar interactions and then induce production of the polyphenylacetylene with high trans-content configuration, which may result in the high degree of extend conjugation of the main chain and enhence the interaction between adjacent pendent groups. Comparing with the model polyphenylacetylene in the absence of phosphaphenanthrene side-groups, TGA analysis reveals the excellent thermal stability of the mono-substituted polyphenylacetylenes containing phosphaphenanthrene as side-groups because the 5% weight loss temperatures are close to 400°C.