Self-inhibition of propagating carbenes in ROMP of 7-oxa-bicyclo[2.2,1]hept-2-ene-5,6-dicarboxylic acid dendritic diesters initiated with Ru(=CHPh)Cl2(PCy3)( 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene)

The kinetic study of the ring-opening metathesis polymerization (ROMP) of exo,exo-7-oxa-bicyclo[2.2.1 ]hept-2-ene-5,6-dicarboxylic acid diethyl ester (2), exo,exo-5,6-bis [[[3,5-bis(3,4(dodecyl-1-oxy)-benzyloxy)]benzyloxy] carbonyl]-7-oxabicyclo [2.2.1] hept-2-ene (3), exo,exo-5,6-bis [[[3,4-bis(3,4,5-(dodecyl-1-oxy)benzyloxy)]benzyloxy] carbonyl]-7-oxabicyclo[2.2.1]hept-2-ene (4), and exo,exo-5,6-bis[[[3,4,5-tris(3,4,5(dodecyl-1oxy)benzyloxy)]benzyloxy] carbonyl]-7-oxa-bicyclo [2.2.1]hept-2-ene (5) initiated with Ru(= CHPh)Cl-2(PCy3)L (L = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (1) and with the novel catalyst Ru(= CH-C6H4-p-CF3)Cl-2(PCy3)L (1-CFs) revealed a competition between ROMP and a facile secondary metathesis reaction between the polymer backbone and the catalyst. Both 1 and 1-CF3 polymerize 2 with a rate of propagation much higher than the rate of initiation and therefore yield polymers with a broad molecular weight distribution. It was demonstrated that the propagation was self-inhibited, and the extent of the secondary metathesis was decreased by increasing the size of the monodendritic side groups of the monomer. Consequently, polymers with narrow molecular weight distribution, i.e., M-w/M-n = 1.05, were obtained from monomer 5 which bears the bulkiest dendritic side groups. These results have demonstrated that, during the ROMP of 5, backbiting and endbiting reactions are eliminated, and only the initiation, propagation, and secondary metathesis by free catalyst take place.