No abstract

Polymeric magnetic materials of the structural type are the focus of this article, in particular ferromagnetic polymers based on coordination complexes or ferrocene. Unlike the composite type of magnetic polymer, which contains added ferrite or magnetic powders, the structural type is an organic or organometallic polymer with intrinsic magnetic properties. Potential application of the ferrocene‐based polymers is expected in areas such as information storage, sensing, drug release, and the fabrication of high frequency microwave devices.

Synopsisa-Hydroxyisopropylferrocene, HPF, was synthesized in good yield and polymerized at 20°C with either SnCI, or BF3.0Et2. The polymerization proceeds by self-alkylation of the stable intermediate ferrocenylcarbenium ion on the cyclopentadienyl ring to form oligomers that contain both homoannular and heteroannular links. The unusually high stability of the a-isopropylferrocenylcarbenium ion was demonstrated by synthesizing and isolating a-isopropylferrocenylcarbenium tetrafluoborate from H P F and using it to initiate the polymerization of styrene. Initiation was successful at 20" and at 0"C, but no polymerization occurred -78°C. The condensation of ferrocene and acetone in the presence of AICI, gave oligomers having structures very similar to those obtained from the cationic polymerization of isopropenylferrocene.

Three types of isopropenylmetallocene monomers were synthesized and subjected to polymerization and copolymerization by cationic initiators; (1) isopropenylferrocene (IF); (2) (η5‐isopropenylcyclopentadienyl)dicarbonylnitrosylmolybdenum (IDM); and (3) 1,1′‐diisopropenylcyclopentadienylstannocene (DIS), and related derivatives of each. IF was synthesized by a three‐step procedure involving the acetylation of ferrocene, conversion of the latter to 2‐ferrocenyl‐2‐propanol, and dehydration of the carbinol. IF was homopolymerized under various cationic initiation conditions, but only low molecular weight homopolymers were obtained. Copolymerization of IF with styrene and with p‐methoxy‐α‐methylstyrene also gave only low molecular weight products. The formation of only low molecular weight polymers in all polymerization reactions is believed to result from the effect of the unusually high stability of ferrocenyl carbenium ions on its propagation reaction. The observed polymerization behavior of α‐trifluoromethylvinylferrocene is in accord with this conclusion. IDM and DIS did not form polymeric products under cationic conditions, although copolymers could be obtained for each of these monomers and styrene with a free radical polymerization initiator (AIBN).