PREPARATION OF DISCRETE POLYENES AND NORBORNENE POLYENE BLOCK COPOLYMERS USING MO(CH-TERT-BU)(NAR)(O-TERT-BU)2 AS THE INITIATOR

Ring-opening metathesis polymerization of TCDT-(CF3)2 [7,8-bis(trifluoromethyl)tricyclo[4.2.2.0(2,5)]deca-3,7,9-triene] by Mo(CH-t-Bu)(NAr)(O-t-Bu)2 (Ar = 2,6-diisopropylphenyl) as a route to polyenes was found to be as controlled as polymerization employing W(CH-t-Bu)(NAr)(O-t-Bu)2, while both TCDT-H-2 and TCDT-(CO2Me)2 gave low yields. Living polyenes could be formed in the Mo system from living poly-TCDT-(CF3)2 and were found to isomerize from the cis to the trans form at the first C = C bond next to the Mo = C bond. Rates of the retro-Diels-Alder reaction and the cis/trans isomerization in both the Mo and W systems were determined by NMR studies. The retro-Diels-Alder in the first unit next to the Mo = C bond takes place approximately 30 times faster than cis/trans isomerization. Living polyenes can be capped with triene dialdehydes to give relatively long polyenes under fairly mild conditions. Acetylene also can be polymerized by Mo(CH-t-Bu)(NAr)(O-t-Bu)2 in a more controlled manner than by W(CH-t-Bu)(NAr)(O-t-Bu)2, although the higher trans content in such polyenes contributes to their greater insolubility and/or tendency to cross-link, even when present as the center block in triblock copolymers containing polynorbornene.