Well-Defined Redox-Active Polymers and Block Copolymers Prepared by Living Ring-Opening Metathesis Polymerization

Mo(CH-t-Bu)(NAr)(O-t-Bu)₂ (1a) in THf/0.1 M [n-Bu₄N]AsF₆ is not oxidized at potentials up to 1.0 V and undergoes a reversible, one electron reduction at −2.16 V vs SCE at a Pt electrode. An analogous intiator containing a ferrocenylmethylidene ligand (1b) can be synthesized by treating 1a with vinylferrocene. Redox-active derivatives of norbornene, containing ferrocene (2) or phenothiazine (3), were prepared and polymerized by 1a or 1b to give living block copolymers containing the ring-opened norbornene derivatives. The living polymer was cleaved from the metal in a Wittig-like reaction with pivaldehyde, trimethylsilylbenzaldehyde, or octamethylferrocenecarboxaldehyde. Polydispersities for the longer block copolymers containing up to ~80 monomer units were found to be as low as 1.05 by GPC. In one case the polydispersity of a homopolymer made from the ferrocene-containing monomer was determined by FD-mass spectroscopy to be 1.06. DSC studies suggest that microphase formation occurs in the block copolymers, even in the case of relatively low molecular weight materials. Solution voltammetric studies of homo and block copolymers showed that the redox centers were electrochemically independent and that all centers exchanged electrons with the electrode. Neutral polymers became insoluble upon oxidation to a polycation, yielding an adsorbed polymer layer on the electrode that could then be cathodically stripped. This oxidative deposition process depended on the electrolyte and the polymer molecular weight but also could be controlled by the size of a nonelectroactive block in the block copolymers. Problems resulting from precipitation of the redox polymers could be circumvented by employing normal pulse voltammetry. Polymers containing redox centers in both end groups as well as in the polymer chain itself have been prepared and their nature confirmed in electrochemical studies.