Poly(ferrocenylmethylsilane): An Unsymmetrically Substituted, Atactic, but Semicrystalline Polymetallocene

Polyferrocenylsilanes (PFSs) [Fe(mu-C5H4)(2)SiRR'](n) are generally atactic and amorphous when unsymmetrically substituted at silicon (R not equal R') but are often able to crystallize if the substitution is symmetrical (R = R'). In this paper we report detailed studies of the ring-opening polymerization (ROP) of [1]methylsilaferrocenophane Fe(mu-C5H4)(2)SiMeH (1) by thermal, anionic and photolytic methods to yield an unsymmetrically substituted yet crystallizable poly(ferrocenylmethylsilane) (PFMS) (R = Me, R' = H) with Me and H substituents at silicon (designated PFMST, PFMSA, and PFMSP, respectively). The structures of the resulting polymers were shown to possess significant differences as revealed by MALDI-TOF mass spectroscopy experiments. For example, PFMSA prepared using n-BuLi as an initiator was shown to contain cyclic contaminants whose formation indicated the existence of backbiting reactions during polymer chain growth. On the other hand, photolytic ROP of 1 using Na[C5H5] as an initiator led only to the formation of linear material but was not a living process due to side reactions between the initiator (and presumably the propagating polymeric anions) and the Si-H groups in the monomer 1. Transition metal-catalyzed ROP of 1 was also explored and, in contrast, was found to afford a hyperbranched and amorphous low molar mass polyferrocenylsilane (4), presumably also as a result of side reactions involving the Si-H groups in the monomer. High resolution H-1 and C-13 NMR spectroscopic studies revealed that PFMST, PFMSA, and PFMSP were all atactic, irrespective of the polymerization route utilized. The crystallization of the samples was investigated by wide-angle X-ray scattering (WAXS), which showed a reflection corresponding to a d-spacing of 6.32 angstrom, by differential scanning calorimetry (DSC), which revealed melting endotherms in the range 106-139 degrees C, and by polarizing optical microscopy (POM).