METALATION AS A TERMINATION STEP IN POLYMERIZATION REACTIONS INVOLVING ALPHA-OLEFINS AND ETHYLENE AS DETECTED BY FIELD DESORPTION MASS-SPECTROMETRY

Field desorption mass spectroscopy (FD-MS) in conjunction with NMR spe ctroscopy has been used to study how olefins larger than ethylene are incorporated into polyethylene using (C(5)Me(5))(2)Sm-based catalysts under hydrogen. Polymerization reactions of propene, 1-pentene, cis- a nd trans-2-pentene, 1-heptene, trans-2-heptene, trans-3-heptene, 1-oct ene, and 1-nonadecene with ethylene under H-2 and with CD2=CD2 under D -2 were studied as well as reactions of ethylene with propene-d(6) and 3,3,3-propene-d(3) using (C(5)Me(5))(2)Sm and (C(5)Me(5))(2)Sm(eta(3) -CH(2)CHCHR) precursors where R = H, Et, and Bu. For the olefins liste d above, the combined analytical techniques with the appropriate deute rium labeling indicate that one olefin is selectively incorporated per polyethylene chain and that incorporation occurs by insertion into a Sm-H bond in the system rather than via an allyl group. Metalation of the olefin by growing polymer chains was found to be competitive with hydrogenolysis as a termination step and can be used to control molecu lar weight. 2-Pentene and 2-heptene do not incorporate as readily as t heir alpha-olefin analogs and 3-heptene incorporation was not detectab le, but these internal olefins are effective termination agents via me talation.