107. Litvinenko, G. I.; Simon, P.F.W.; Müller, A.H.E.: Molecular parameters of hyperbranched copolymers obtained by self-condensing vinyl copolymerization, 1. Equal rate constants, Macromolecules 32, 2410 (1999) | |
Abstract: The kinetics, molecular weight averages and the average degree of branching, DB, are calculated analytically for the self-condensing vinyl copolymerization (SCVCP) of a vinyl monomer M with an "inimer" AB*, i.e., a molecule having a vinyl group A and an initiating group B*. MWD and DB strongly depend on the monomer/inimer ratio g = M_{0}/I_{0} (or the "dilution factor", g + 1 = (M_{0} + I_{0})/I_{0}). At low conversions, the process resembles a living polymerization of M, where the AB* inimers act as initiators only; at high conversions, the process resembles a self-condensing vinyl homopolymerization (SCVP) of AB* inimers. For a high monomer/inimer ratio (g >> 1), the number-average molecular weight, M_{n}, is given by the product of the values for the SCVP of inimer and the living polymerization of monomer initiated by inimer. For a given M_{n} value, the polydispersity index decreases with g. For g > 1, DB decreases with g, however, the DB values are 4 times higher than expected from the "dilution" of AB* molecules by M molecules. For low values of g, DB even exceeds the values for a homo-SCVP; a maximum of DB = 0.5 is reached at g = 0.6. These effects can be explained by the addition of monomer molecules to in-chain active centers (i.e., in linear segments) leading to very short branches. The trends predicted by our calculations are confirmed by preliminary experimental data. |