Monotelechelic Poly(oxa)norbornenes by Ring-Opening Metathesis Polymerization using Direct End-Capping and Cross Metathesis.
Two different methodologies for the synthesis of monotelechelic poly(oxa)norbornenes prepared by living ring-opening metathesis polymerization (ROMP) are presented. The first method, termed direct end-capping, is carried out by adding an internal cis-olefin terminating agent (TA) to the reaction mixture immediately after the completion of the living ROMP reaction. The second method relies on cross metathesis (CM) between a methylene-terminated poly(oxa)norbornene and a cis-olefin TA mediated by the ruthenium olefin metathesis catalyst (H(2)IMes)(Cl)(2)Ru(CH-o-OiPrC(6)H(4)) (H(2)IMes = 1,3-dimesitylimidazolidine-2-ylidene). TAs containing various functional groups, including alcohols, acetates, bromides, a-bromoesters, thioacetates, N-hydroxysuccinimidyl esters and Boc-amines, as well as fluorescein and biotin groups, were synthesized and tested. The direct end-capping method typically resulted in >90% end-functionalization efficiency, while the CM method was nearly as effective for TAs without polar functional groups or significant steric bulk. End-functionalization efficiency values were determined by (1)H NMR spectroscopy.
Matson
John B
JB
NanoSystems Biology Cancer Center, Division of Chemistry and Chemical Engineering, MC 127-72, California Institute of Technology, Pasadena, California 91125.
Grubbs
Robert H
RH