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Copolymerization of 1‐(trimethylsilyl)‐1‐propyne (MeC ≡ CSiMe3) with several aromatic and aliphatic disubstituted acetylenes (MeC ≡ CPh, n‐BuC ≡ CPh, 2‐octyne, and 4‐octyne) were examined by using Ta and Nb catalysts. The TaCl5–Ph3Bi catalyst was effective in copolymerization with the aromatic acetylenes, whereas the NbCl5–Ph3Bi catalyst was preferable in copolymerization with the aliphatic acetylenes. The copolymerization products were not mixtures of homopolymers but copolymers. The relative reactivity of monomer tended to decrease with increasing steric effect of monomer: 2‐octyne > MeC ≡ CSiMe3 > 4‐octyne > MeC ≡ CPh > n‐BuC ≡ CPh. The copolymers of MeC ≡ CSiMe3 with MeC ≡ CPh [copoly(TMSP/PP)s] had high molecular weight (Mw > 1 × 106), and provided thermally stable tough films. With increasing MeC ≡ CPh content of copoly(TMSP/PP), the oxygen permeability coefficient (P italicO 2) decreased, while the separation factor (P italicO 2/P italicN 2) increased.

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

Polymerization of homologues of 1‐(trimethylsilyl)‐1‐propyne [CH3CCSi(CH3)3] was studied. CH3CCSi(CH3)2(n‐C6H13) (I) polymerized with 1 : 1 mixtures of TaCl5 and organometallic cocatalysts (e.g., Ph4Sn and Ph3Bi) to produce in good yields a polymer having a weight‐average molecular weight (Mw) over 1 × 106. CH3CCSi(CH3)2 Ph (II) and CH3CCSi(C2H5)3 (III) formed polymers having Mw's of ∼ 5 × 105 in moderate yields in the presence of TaCl5‐based catalysts. In contrast, none of CH3CCSi(CH3)2(i‐C3H7), CH3CCSi(CH3)2(t,‐C4H9), C2H5CCSi(CH3)3, and n,‐C4H9CCSi(CH3)3 polymerized, which is attributed to the steric effect of the monomers. Some other 1‐silyl‐1‐propynes also failed to polymerize. The three new polymers formed from (I)–(III) had the structure \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} [{\rm CCH}_{\rm 3} \hbox{=\hskip-2pt=} {\rm C(SiRR'R''}\rlap{--} ]_n$\end{document} according to IR and 13C‐NMR spectra. They were white solids, soluble in low‐polarity solvents (e.g., toluene and chloroform) and stable enough in air at room temperature.