d0/fn-mediated ring-opening ziegler polymerization (ROZP) and copolymerization with mono- and disubstituted methylenecyclopropanes.: Diverse mechanisms and a new chain-capping termination process

The mono- and disubstituted methylenecyclopropane derivatives 2-phenyl-1-methylenecyclopropane (A) and 7-methylenebicyclo[4.1.0]heptane (B) have been successfully implemented in ring-opening Ziegler polymerization. Homogeneous ethylene + 2-phenyl-1-methylenecyclopropane (A) random copolymerizations are mediated efficiently by the single-site kcatalysts Cp*2ZrMe+B(C6F5)(4)(-), [Cp*2LuH](2), [CP*2SmH](2), and [Cp*2YH](2) (CP* = C5Me5) to produce a copolymer (C) with A enchained in a ring-opened fashion. Single-site coordinative polymerization of 7-methylenebicyclo[4.1.0]heptane (B) proceeds via either ring-opened or ring-unopened pathways. In the presence of CP*2ZrMe+ MeB(C6F5)(3)(-) at 0degreesC, B undergoes polymerization to afford the insoluble, ring-unopened homopolymer D, which was characterized by CPMAS NMR, DSC, elemental analysis, FTIR, TGA, and XRD. The melting point of polymer D lies above its decomposition temperature (>300 degreesC). Random copolymerizations of B and ethylene mediated by Cp*2ZrMe+MeB(C6F5)(3)(-) at room temperature result in polymer E, a polyethylene capped by a ring-opened B fragment. The formation of B-capped polymer E is a consequence of a new chain transfer mechanism, as evidenced by a linear relationship between M-n and [B](-1). The rate constant for insertion of ethylene is similar to25 x greater than the rate constant for insertion of monomer B into the metal-alkyl bond. Random copolymers (F) of ring-opened B and ethylene are produced when the catalysts Me2Si(Me4C5)((BuN)-Bu-t)ZrMe2, Me2Si(Me4C5)((BuN)-Bu-t)TiMe2 (activated by either (C6H5)(3)C+B(C6F5)(4)(-) or B(C6F5)(3)), and [CP*2LuH](2) are employed.