SYNTHESIS OF ABA TRIBLOCK COPOLYMERS OF NORBORNENES AND 7-OXANORBORNENES VIA LIVING RING-OPENING METATHESIS POLYMERIZATION USING WELL-DEFINED, BIMETALLIC RUTHENIUM CATALYSTS

Norbornene and 7-oxanorbornene derivatives were polymerized by ring-op ening metathesis polymerization (ROMP) in a living manner by employing three new well-defined, bimetallic ruthenium catalysts (PR(3))(2)Cl2R u(=CH-p-C6H4C(H)=)RuCl2(PR(3))(2) [R = Ph, 1; R = Cy (cyclohexyl), 2; R = Cyp (cyclopentyl), 3] as initiators to obtain ABA triblock copolym ers with low polydispersities. 1-3 were synthesized via alkylidene tra nsfer from 1,4-bis(alpha-diazomethyl)benzene to RuCl2(PPh(3))(3) and s ubsequent phosphine exchange. Reactions of 7-oxanorbornenes 5 and 6 or a silicon-containing norbornene 7 with 3 resulted in polymers with lo w polydispersities ranging from 1.10 to 1.22, while polymerizations in itiated by 2 displayed higher polydispersities ranging from 1.20 to 1. 35. Polymerizations of 5-7 catalyzed by 2 and 3 fulfill the requiremen ts for a living polymerization. However, catalyst 1 is not reactive en ough to polymerize functionalized norbornenes or 7-oxanorbornenes. The living polymerizations were successfully used to prepare three ABA tr iblock copolymers of monomers 5-7. In all cases, these ABA triblock co polymers have higher molecular weights than the homopolymers, and all polydispersities remained low.