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 t rans, 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) (1 d) (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 e xperiments 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 w ith 1a as the initiator are atactic while high cis polymers prepared w ith 1d as the initiator are isotactic. Bimodal molecular weight distri butions were observed in some cases when 1d was employed, consistent w ith slightly different rates of polymerization of enantiomerically pur e substrate by the two different enantiomers of the racemic initiator.