POLYMERIZATION OF ENANTIOMERICALLY PURE 2,3-DICARBOALKOXYNORBORNADIENES AND 5,6-DISUBSTITUTED NORBORNENES BY WELL-CHARACTERIZED MOLYBDENUM RING-OPENING METATHESIS POLYMERIZATION INITIATORS - DIRECT DETERMINATION OF TACTICITY IN CIS, HIGHLY TACTIC AND TRANS, HIGHLY TACTIC POLYMERS

The ring-opening metathesis polymerization (ROMP) of enantiomerically pure dicarboalkoxynorbornadienes (2,3-(CO(2)R*)(2)-norbornadiene where R* = (1R,2S,5R)-(-)-menthyl (2a) or (R)-(-)-pantalactonyl (2b)) with Mo(CHCMe(2)Ph)(NAr)(O-t-BU)(2) (1a) (Ar = 2,6-i-Pr2C6H3) yields high trans, highly tactic polymers. The ROMP of chiral monomers 2a,b with Mo(CHCMe(2)Ph)(NAr)[OC(CF3)(3)](2) (1b), Mo(CHCMe(2)Ph)(NAr')[BIPH(t-Bu)(4)] (1c), and Mo(CHCMe(2)Ph)(NAr') [(+/-)-BINO(SiMe(2)Ph)(2)](THF) (1d) (Ar' = 2,6-Me(2)C(6)H(3)) yields high cis, highly tactic polymers. Tacticities can be determined directly by homonuclear (proton/proton) correlation spectroscopy and decoupling experiments. The cis polymers were found to be isotactic, the trans polymers syndiotactic. Related experiments employing enantiomerically pure disubstituted norbornenes (2,3-dicarbomethoxynorborn-5-ene, 2,3-dimethoxymethylnorborn-5-ene, and 5,6-dimethylnorborn-2-ene) showed that high trans polymers prepared with 1a as the initiator are atactic while high cis polymers prepared with 1d as the initiator are isotactic. Bimodal molecular weight distributions were observed in some cases when 1d was employed, consistent with slightly different rates of polymerization of enantiomerically pure substrate by the two different enantiomers of the racemic initiator.