Alkylaluminophosphonate-catalyzed ring-opening homopolymerization of epichlorohydrin and propylene oxide

Reactions of an aluminum alkyl, AlR3 (R = Me, Et, Bu-i, Bu-t), with a phosphonic acid, R'P(O)(OH)(2) (R' = H, Me, Bu-i, Ph), in molar ratios of 3.1, 2:1, and 1:1 were conducted in toluene-TNF. Resulting aluminophosphonate solutions were screened for catalytic activity for the ring-opening homopolymerization of epichlorohydrin (ECH) and propylene oxide (PO). A highly active catalyst solution, 3a, was obtained from reaction of (Bu3Al)-Bu-t with MeP(O)(OH)(2), in a 2:1 molar ratio in toluene-THF. A more active catalyst, 3b, was obtained by removing volatiles, specifically THF, from solutions of 3a and reconstituting with toluene. Catalyst 3a polymerized ECH at 60 degrees C in 1-3 h to an elastomer with molecular weight, M-n, of 103 000 and polydispersity, M-w/M-n, of 1.9. Catalyst 3b yielded poly-ECH with M-n of 130 000 and M-w/M-n of 1.9 within 15 min. Catalysts 3a and 3b polymerized PO to oily oligomers with M-n of 3588 and 4046 and M-w/M-n of 1.1 and 1.2, respectively. Known dimeric and tetrameric aluminophosphonates such as [(Bu2AlO2P)-Bu-t(OSiMe3)Ph](2) and [RAlO3PR'](4) (R = Me, R' = Me; R = Bu-t, R' = Me, Ph) do not account for the observed activity of the catalyst solutions. Comparisons of catalytic activity with that for well-defined catalysts and a structural analogy of alkylaluminophosphonates to cyclic and cage tert-butylaluminoxanes are presented. (C) 2000 Elsevier Science S.A. All rights reserved.