Polymerization of (o-Phenylphenyl)acetylene and (2,5-Di-tert-butylphenyl)-acetylene and Polymer Properties

Abstract

KEY WORDS(o-Phenylphenyl)acetylene / (2,5-Di-tert-butylphenyl)acetylene / Substituted Acetylene/ Metathesis Polymerization/ Transition-Metal Catalyst / Thermal Stability / In the polymerization of monosubstituted acetylenes by W and Mo catalysts, a general tendency has been observed that monomers with bulky substituents provide high molecular weight polymers. Thus, it has recently been found that highly sterically crowded phenylacetylenes (PAs) having bulky groups at the ortho position produce polymers in good yields, and the product polymers have higher molecular weights than that of poly(phenylacetylene) [poly(PA)]: e.g., poly(HC = CC 6 H 4 -o-iso-Pr), weight-average molecular weights (Mw) 1 x 10 6 ;1 poly(HC::CC 6 H 4 -o-GeMe 3 ), Mw 7 x 10 5 ;2 and poly(HC::CC 6 H 3 -2-SiMe 3 -4-OSiMei-t-Bu), Mw 9xl05; 3 cf poly(PA), Mw 3xl0 4 • Consequently these ortho-substituted poly(PAs) can be fabricated into tough films unlike poly(PA). Therefore it will be interesting to examine the effect of as bulky or even bulkier ortho hydrocarbon groups on the polymerizability, polymer molecular weight and polymer properties of PAs.The present note deals with the polymerization of P As having a very bulky hydrocarbon group at the ortho position. The monomers used are (o-phenylphenyl)acetylene (o-PhPA) and (2,5-di-tert-butylphenyl)acetylene [2,5-(tBu)2PA]. The structure and properties of the product polymers have also been invesitigated. EXPERIMENTALThe two monomers (new compounds) were synthesized according to Scheme 1; i.e., o-PhPA was prepared by the Sandmeyer reaction 4 of o-aminobiphenyl followed by Pd-catalyzed coupling with 2-methyl-3-butyn-2-ol and base-catalyzed acetone elimination. 5 o-PhPA: bp l00°C (3mmHg), d 1.079. 2,5-(t-Bu) 2 PA was prepared from benzene via 1,4-di-tert-butylbenzene 6 and its iodination product 7 and then in a similar way. 2,5-(t-Bu)z PA: bp 140°C (3 mmHg), d 0.899. Transitionmetal compounds and organometallic cocatalysts were commercially obtained, and used without further purification.