SOLID-STATE NMR-STUDY OF POLY(PHENYLACETYLENE) SYNTHESIZED WITH A RHODIUM COMPLEX INITIATOR

The polymerization mechanism and the structure of poly(phenylacetylene ) synthesized using the Rh(C=CC6H5)(2,5-norbornadiene)[P(C6H5)(3)](2) initiator were investigated by solid-state NMR. The C-13 Fake doublet of the poly(phenylacetylene) containing 5% [1,2-C-13]phenylacetylene w as observed by effectively removing the chemical shift anisotropies us ing a composite inversion pulse sequence. The C-13-C-13 bond distance was determined to be 1.386 Angstrom from the spectrum, which correspon ds to a double bond length. This result clearly shows that the polymer ization by the Rh initiator progresses by the cis-insertion mechanism. The C-13 isotropic chemical shifts of the protonated and nonprotonate d olefin carbons were deduced to be 131.8 and 141.4 ppm, respectively, from differences between some overlapped CPMAS spectra. Two-dimension al C-13 CPMAS exchange experiments revealed conformational inhomogenei ty of the main chain and the presence of slow pi-flip motion of the ph enyl ring.