Molecular parameters of hyperbranched copolymers obtained by self-condensing vinyl copolymerization.: 1.: Equal rate constants

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 gamma = M-0/I-0 (or the "dilution factor", gamma + 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 (gamma much greater than 1), the number-average molecular weight, (M) over bar(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) over bar(n) value, the polydispersity index decreases with gamma. For gamma > 1, DB decreases with gamma, however, the DB values are 4 times higher than expected from the "dilution" of AB* molecules by M molecules. For low values of gamma, DB even exceeds the values for a homo-SCVP; a maximum of DB = 0.5 is reached at gamma approximate to 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.