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Rapid Commun, 28, pp. 1761-1775. , and references herein; Blouin, N., Michaud, A., Gendron, D., Wakim, S., Blair, E., Neagu-Plesu, R., Belletete, M., Leclerc, M., (2008) J. Am. Chem. Soc, 130, pp. 732-742; Mullekom, H.A.M.V., Vekemans, J.A.J.M., Havinga, E.E., Meijer, E.W., (2001) Mater. Sci. Eng., R, 32, pp. 1-40; Hong, X.M., Tyson, C.J., Collard, D.M., (2000) Macromolecules, 33, pp. 3502-3504; Sheina, E.E., McCullough, R.D., (2004) Polym. Prepr, 45, pp. 800-801; It was previously demonstrated for related Suzuki chain-growth polycondensation having a similar catalyst-transfer mechanism that Pd(0) catalytic species are able to transfer intramolecularly over a 1 nm long fluorene moiety: (a) Calhorda, M. J, Brown, J. M, Cooley, N. A. Organometallics 1991, 10, 1431-1438; Dong, C.-G., Hu, Q.-S., (2005) J. Am. Chem. Soc, 127, pp. 10006-10007; Sinclair, D.J., Sherburn, M.S., (2005) J. Org. Chem, 70, pp. 3730-3733; Weber, S.K., Scherf, U., (2006) Org. 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Sci, 31, pp. 277-278; Matyjaszewski, K., Gaynor, S., Wang, J.-S., (1995) Macromolecules, 28, pp. 2093-2095; An unintended mismatch between the relative amounts of 6 and tBuMgCl during the GRIM procedure is quite probable because of difficulties to dose precisely small portions of BuMgCl solution and a high sensitivity of BuMgCl to the moisture and air; Assignment and evaluations of 1H NMR spectra were performed as described for the experiment corresponding to entry 3, Table 1 (see also Supporting Information); For given conversions of the monomers (Table 1) DP values must not exceed 10 if the polycondensation proceeds via the step-growth mechanism. For example, at 90% conversion DP = 1/1-0.9 = 10 is expected: (a) Carothers, W. H. J. Am. Chem. Soc. 1929, 51, 2548-2559; Flory, P.J., (1953) Principles of Polymer Chemistry, , Cornell University Press: Ithaca, Chapters III and VIII; Since the mass of the Br atom (80) is close to the mass of the Ph moiety (77) the polymerization mixture was treated to tBuMgCl prior to MALDI-TOF measurements according to the procedure described by McCullough et al. to reduce any existing Br end groups. 1H NMR data confirmed a quantitative reduction of Br atoms, and thus, the signals with m/z = 499 + 78 belong to Ph/H-poly3a, whereas the signals with m/z = 499 + 2 belong to H/H-poly3a (Figure 2); [Ph-poly] = 5DP and S = [Ph-poly] 1/DP, where [Ph-poly] is the fraction of Ph-terminated products in the polymerization mixture, S is the selectivity of the chain-growth (intramolecular catalyst transfer) elementary step, and DP is the mean polymerization degree. .Sph.poly2a = [Ph-poly2a] 1/15 = 0.871/15 = 0.99 (99%); SPh-poly3a = [Ph-poly3a]1/12 = 0.691/12 = 0.97 (97%); S Ph-poly2b = [Ph-poly2b]1/10 = 0.451/10 = 0.923 (92.3%); Sph-poly3b = [Ph-poly3b]1/10 = 0.311/9 = 0.88 (88%); Hidai, M., Kashiwagi, T., Ikeuchi, T., Uchida, Y., (1971) J. Organomet. Chem, 30, pp. 279-282 |