| 87. Yan, D.Y.; Müller, A.H.E.; Matyjaszewski, K.: Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization, 2.Degree of branching, Macromolecules 30, 7024 (1997) | |
| Abstract: Using a modified definition, the average degree of branching,  , the
fraction of
branchpoints,
 , as
well as the fractions of various structural units are calculated as a
function of
conversion of double bonds for hyperbranched polymers formed by
self-condensing vinyl polymerization
(SCVP) of monomers (or "inimers") with the general structure AB*,
where A is a vinyl group and B* is
an initiating group. The results are compared to those for the
polycondensation of AB2-type monomers.
At full conversion,
 is
somewhat smaller for SCVP
( 
 0.465) than for AB2 systems
(
= 0.5).
There are two kinds of linear groups in SCVP whereas there is only
one kind in AB2 systems. Since
there are two different active centers in SCVP, i.e., initiating B* and
propagating A* centers, the effect
of nonequal reactivities on
 is
also discussed. At a reactivity ratio of the two kinds of active
centers,
r = kA/kB 2.59, a
maximum value of
= 0.5 is reached. For the limiting case r << 1, a
linear
polymer resembling a polycondensate will be formed whereas for
r >> 1 a weakly branched vinyl polymer
is expected. NMR experiments allow for the determination of
reactivity ratio r. |
Prof. Dr. Axel Müller
|
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