Pressure-Induced cis-to-trans Isomerization of Poly[(p-methylthiophenyl)acetylene] Prepared with a [Rh(norbornadiene)Cl]2 Catalyst – A Raman, UV-Vis, and ESR Study

A stereospecific polymerization of a novel aromatic acetylene containing an alkyl sulfide group, i.e., (p-methylthiophenyl)acetylene (pMeSPA) was successfully performed to selectively give the corresponding polymerbearing a cis-transoid structure as a main geometrical form and a very high molecular weight, M n =1.7-5.8 ×10 6 in high yields. This was accomplished when a Rh complex catalyst, [Rh(norbornadiene)Cl] 2 was used in the presence of triethylamine (TEA) solvent as a cocatalyst and its mixed solvents with TEA, together with a detailed characterization of the resulting polymers before and after compression at room temperature. Based on the data obtained before and after compression, it was concluded that compression of the PpMeSPA polymers induced a cis-to-trans isomerization at room temperature under vacuum even in the solid state (the Figure shows the radical generated by compression).