| 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 AB2 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 (kA 
kB) have a
strong effect on kinetics and MWD. The MWD narrows down to
w/n = 2
for kA  kB
(corresponding to
the common polycondensation of AB monomers) but broadens for
kB > kA. Several
deviations from ideal
behavior are discussed. |
Prof. Dr. Axel Müller
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