Ring-Opening Copolymerization of Cyclotetrasilanes and Silicon-Bridged [1]Ferrocenophanes:  Synthesis and Properties of Polysilane−Poly(ferrocenylsilane) Random Copolymers

Abstract

Novel poly(methylphenylsilane)-poly(ferrocenyldimethylsilane) copolymers 5a-d of varying monomer composition were prepared via the thermal ring-opening polymerization of a mixture of the strained cyclic tetrasilane [MePhSi]4 (1) and the silicon-bridged [1]ferrocenophane Fe(η-C5H4)2SiMe2 (3). The resulting materials were structurally characterized by 1 H and 29 Si NMR and also by gel permeation chromatography (GPC), pyrolysis mass spectrometry (MS), and cyclic voltammetry. GPC in THF indicated that the molecular weights of the polymers 5a-d were in the range Mn ) (2.0 × 10 4 )-(8.9 × 10 4 ) with PDI values of 2.4-3.5. Polymers 5a-c were photosensitive and GPC traces of 5a-c were studied both before and after irradiation of the sample with UV light (λ ) 340 nm). The formation of short chain oligo(ferrocenylsilanes) after irradiation was consistent with exclusive photodegradation of the polysilane segments and indicated that the copolymers were random in nature. Pyrolysis MS of 5a-c also supported a random structure. Cyclic voltammetric studies of 5a-c in CH2Cl2 showed the presence of the characteristic two reversible oxidation waves arising from oligo(ferrocenylsilane) segments with interacting iron atoms at E1/2 ) 0.00 and 0.23 V (relative to ferrocene/ferrocenium) and an irreversible oxidation with Ep(ox) ) 0.39 V arising from the polysilane segments. UV/vis spectroscopy showed that the σ-electrons in the oligosilane segments are delocalized and that λmax increased from 325 to 333 nm as the proportion of the cyclotetrasilane 1 in the initial monomer mixture increased. These values suggest that the oligosilane segments are relatively short and do not approach the limit corresponding to ca. 30 silicon atoms (Mn ) ca. 3 000), which levels off at 338 nm. Attempted anionic initiation of the copolymerization of 1 and 3 was unsuccessful and led exclusively to homopolymerization. Transition metal catalyzed copolymerization of 1 and 3 using PtCl2 resulted in a copolymer which was derived almost exclusively from 3. The charge transport properties of the representative copolymer 5d were also investigated. Films of pristine 5d were insulating (conductivity <10 -14 S cm -1 ) but after exposure to iodine the conductivity increased by a factor of 10 8 to (6.5-8.2) × 10 -6 S cm -1 . In comparison, the conductivities of iodineexposed films of poly(ferrocenyldimethylsilane) (4) and poly(ferrocenyldi-n-butylsilane) (7) were ca. 2 × 10 -4 S cm -1 . The hole mobility of 5d was studied by standard time of flight techniques and was found to be appreciable with a value of 4.0 × 10 -6 cm 2 /V s.

Organometallic Ferrocene- and Phosphorus-Containing Polymers: Synthesis and Characterization

“…It has been reported that the initial oxidation occurs at alternating iron sites and subsequent oxidation occurs at a higher potential due to the charge repulsion between the iron sites [31]. In addition, it was reported that doped ferrocene polymers possess semiconductor characteristics [32]. It is contemplated that the differences between the bridging moieties in ferrocene polymers affect their electronic properties such as metal-metal interaction and electrical conduction.…”

“…Polyferrocenylsilanes bearing alkyl, alkoxy, aryloxy and amino groups are typical. When symmetrically substituted, PFSs are often semicrystalline, whereas asymmetrically substituted materials are generally amorphous [32]. Additionally, the presence of iron in PFSs imparts unique properties that are otherwise not found or difficult to acquire with traditional organic polymers.…”

Polyferrocenylsilanes as Protective Charge Migration Coatings for Dielectrics

“…)1 ) have been established [25,26]. However, the polyferrocenes in their pristine state are insulating (conductivities less than 1 Â 10 )14 SAEcm )1 ) [26].…”

“…However, the polyferrocenes in their pristine state are insulating (conductivities less than 1 Â 10 )14 SAEcm )1 ) [26]. We were therefore interested in investigating additional properties of polyferrocenylsilanes including their dielectric properties in comparison with other commercially available organic polymers.…”

“…Given current knowledge of the charge transport properties of polyferrocenylsilanes, it is plausible to imagine of the coatings of PFSs 3 and 4 acting as semiconductors [25,26]. In essence, the charge being directed at the surface of the coated sample might therefore be slowly drained to the ground by contact with the edges of the grounded mask aperture.…”