Recently, not only the polymerization of acetylene but also that of substituted acetylenes has been intensively ~t u d i e d .~ We have succeeded in the synthesis of various substituted polyacetylenes.4 1-(Trimethylsily1)-1-propyne [CH3C=CSi(CH3),] polymerizes with the pentahalides of tantalum and niobium (TaC1, and NbC1,) alone 2b,5 to give a new polymer having weight-average molecular weights (i@$s) of 1 X 105-1 X 10,. Poly[l-(trimethylsily1)-1propyne] is white, soluble, air-stable, and electrically insulating, which gives a striking contrast to the properties of polyacetylene. Further, this polymer has proved to exhibit the highest oxygen permeability among all the existing polymer^.^,^ Organometallics of group 4 and 5 main-group metals (e.g., Ph4Sn, EhSiH, Ph3Bi) work as weak reducing agents and eventually play important roles as cocatalysts in the polymerization of substituted acetylenes by group 5 and 6 transition-metal catalysts. For instance, the polymerization of disubstituted acetylenes (e.g., 1-phenyl-1-propyne, 2-octyne, 1-chloro-2-phenylacetylene) by WCl, or MoCl, yields polymers only in the presence of these cocatalyst^.^ As another example, polymer degradation occurs in the polymerization of 1-phenyl-1-propyne by TaC1, and NbCl,, whereas it is restrained in the presence of the cocatalysts, resulting in the formation of high molecular weight poly-(1-phenyl-1-propyne) .7Here we report the synthesis of high molecular weight poly[l-(trimethylsily1)-1-propyne] with a catalyst system composed of a equimolar mixture of TaC1, and Ph3Bi [1:1 TaC1,-Ph3Bi]. In the course of our study on the cocatalyst effect, it was found that the TaC1,-Ph3Bi catalyst achieves extremely high MW, up to 4 x 10,. This molecular weight is the highest among those of the substituted polyacetylenes ever k n~w n .~~~ The influences of various cocatalysts and polymerization conditions are also discussed. Table I shows the effect of various cocatalysts on the polymerization of 1-(trimethylsily1)-1-propyne by TaC1, and NbC1,. Polymerizations were run in toluene at 80 "C for 24 h. TaC15 alone yielded quantitatively poly[l-(tri-methylsily1)-1-propyne] having a M, somewhat lower than 1 x lo6 [i@$s and number-average molecular weights ( &f ; s) were determined by gel permeation chromatography (GPC)]. It is of great interest that an equimolar mixture of TaC1, and Ph3Bi afforded the polymer with &fw as high as 4 X lo6 without reducing the polymer yield. Organoantimony, -tin, and -silicon cocatalysts also increased the 0024-9297/86/2219-2448$01.50/0 0 Table I Polymerization of 1-(Trimethylsily1)-1-propyne by Various TaC1,-and NbC1,-Based Catalysts" polymerb yield, % $fw X M, X catalvst
Results and Discussion