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)Cl-2(PCy3)( 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene)

The kinetic study of the ring-opening metathesis polymerization (ROMP) of e xo,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] ca rbonyl]-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)]be nzyloxy] 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 w ith the novel catalyst Ru(= CH-C6H4-p-CF3)Cl-2(PCy3)L (1-CFs) revealed a co mpetition between ROMP and a facile secondary metathesis reaction between t he 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 y ield polymers with a broad molecular weight distribution. It was demonstrat ed 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 bear s the bulkiest dendritic side groups. These results have demonstrated that, during the ROMP of 5, backbiting and endbiting reactions are eliminated, a nd only the initiation, propagation, and secondary metathesis by free catal yst take place.