86. Müller, A.H.E.; Yan, D.Y.; Wulkow, M.: Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization, 1. Molecular weight distribution, Macromolecules 30, 7015 (1997) | |

Abstract:The molecular weight distribution (MWD) and its moments are calculated for hyperbranched polymers formed by self-condensing vinyl polymerization (SCVP) of monomers ("inimers") with the general structure AB*, where A is a vinyl group and B* is an initiating group. The calculated MWD is extremely broad, the polydispersity index (PDI) being equal to the number-average degree of polymerization: _{w}/_{n}
= _{n}. It is twice as broad as that
for the polycondensation of AB_{2} type monomers. If the
fraction of
unreacted monomer is not taken into account, the MWD becomes somewhat
narrower,
'_{w}/'_{n}
0.40'_{n}.
The kinetics of the polymerization process are first order with
respect to the concentration of vinyl groups;
_{n}, _{w}, and
PDI increase exponentially with time. Comparison of the
theoretical results with experimental
data indicates that the rate constant of addition of an active center
to a vinyl group decreases with
increasing degree of polymerization. Since there are two different
active centers in SCVP, namely
initiating ones, B*, and propagating ones, A*, nonequal reactivities of
the two centers (k_{A}
k_{B}) have a
strong effect on kinetics and MWD. The MWD narrows down to
_{w}/_{n} = 2
for k_{A} k_{B}
(corresponding to
the common polycondensation of AB monomers) but broadens for
k_{B} > k_{A}. Several
deviations from ideal
behavior are discussed. |