Polymerization, structures and thermal properties of phosphaphenanthrene- containing poly ( 1-pentyne)

The phosphaphenanthrene-containing 1-pentyne monomer (M-34) was synthesized through the successive esterification of 2-( 6-oxide-6H-dibenz < c,e > < 1 ,2 > oxaphos-phorin-6-yl)-dihydroxyphenylene (ODOPB) with 4-(4-pentynoxy) benzoyl and 4-butyloxybenzoyl, respectively. Due to the introduction of 9,10dihydro-9-oxa-lO-phosphaphenanthrene 10-oxide (DOPO) group, the catalytic ability of Rh-based catalysts ( [ Rh(nbd)Cl]₂ and Rh ( nbd) B ( C₆H₅ )₄ ) is decreased and the yields of polymer are relatively low. The polymerization of model monomer (M-O) in the absence of phosphaphenanthrene side-group was, however, carried out in high yield at the same condition. The microstructure of the poly ( 1-pentyne) dérivants was characterized by means of ¹H-NMR. The experimental results indicate that the main-chains of poly ( 1-pentyne) dérivants with high trans-content configuration are produced due to the strong π-π stacking and polar interactions between phosphaphenanthrene- containing pendent groups. Thus, the interaction between adjacent pendent groups is further strengthened. The molecular weights and distribution of P-34 and its model polymer P-O were measured by GPC; Their thermal properties were evaluated by TGA and DSC. Comparing with P-O in the absence of phosphaphenanthrene side-group,TGA analysis reveals the excellent thermal stability of P-34, losing 1% of weights during heating to 270°C and retaining 50% of weights after pyrolyzis at 55°C And the char yield of P-34 is over 50 wt% at 550 ^°C. The DSC results indicate that T_g of P-34 is lower than that of P-O because DOPO increases the volume of side-groups in P-34.