Synthesis of regio- and stereoregular poly(silylenearylenevinylene)s by the hydrosilylation of AB_x type monomers and properties of the formed polymers

Polymerization of p-(dimethylsilyl)phenylacetylene in toluene at 25 and 80°C using Rhl(PPh₃)₃ catalyst afforded highly regio- and stereoregular poly(dimethylsilylenephenylenevinylene)s (cis-2 and trans-2) containing 98% cis- and 99% trans-vinylene moieties, respectively. Similarly, poly(dimethylsilylenebiphenylenevinylene)s (5's with 74% cis- and 89% trans-structures) were prepared. The trans-type polymers showed red shifts and hyperchromic effects in the UV-visible spectrum compared to the cis-type counterparts. Photoirradiation of both cis-2 and trans-2 gave cis-rich mixtures at the equilibrium state. The degree of photoisomerization could be exactly evaluated by comparing the UV spectra of solutions of cis-2 and trans-2 before and after photoirradiation. The trans and cis polymers exhibited different emission properties: e.g., trans-2: emissn λ_max=400 nm, quantum yield=3.4 × 10^-3; cis-2: emissn λ_max=380 nm, quantum yield=1.5 × 10^-3. The quantum yield of the trans-rich 5 was especially high and reached 0.15. Interestingly, the onset temperature of weight loss of cis-2 was ca. 510°C, and much higher than that (ca. 280°C) of trans-2. In addition, polymerization of bis(4-ethynylphenyl)methylsilane catalyzed by RhI(PPh₃)₃ afforded a regio- and stereoregular hyperbranched poly(dimethylsilylenephenylenevinylene) containing 95% transvinylene moiety. This polymer displayed an absorption due to π-π* transition around 275 nm as a shoulder and a weak absorption around 330 nm due to π-to-σ* charge transfer, which was hardly seen with the corresponding linear polymer, trans-2.