142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

48 B. Charleux, R. Faust
3.3
Macromonomers
A macromonomer is a macromolecule with a reactive end group that can be
homopolymerized or copolymerized with a small monomer by cationic, anionic,
free-radical, or coordination polymerization (macromonomers for stepgrowth
polymerization will not be considered here). The resulting species may
be a star-like polymer (homopolymerization of the macromonomer), a comblike
polymer (copolymerization with the same monomer), or a graft polymer
(copolymerization with a different monomer) in which the branches are the
macromonomer chains.
Macromonomers have been synthesized by living cationic polymerization by
three different techniques: by the use of a functional initiator, employing functional
capping agent or by chain end modification.
3.3.1
Synthesis of Macromonomers by Living Cationic Polymerization
3.3.1.1
Synthesis Using a Functional Initiator
This technique is the simplest as it generally requires only one step since the polymerizable
function is incorporated via the initiator fragment. To obtain welldefined
macromonomers with one polymerizable end group per chain, controlled
length and narrow MWD, the following criteria should be fulfilled:
– initiation only from the initiator (no protic or direct initiation);
– living polymerization conditions (especially no transfer to the monomer);
– during the polymerization the functional group should remain unreacted or
it needs to be protected.
3.3.1.1.1
Poly(vinyl ethers)
Most of the reported poly(vinyl ether) macromonomers have been prepared
with a methacrylate end group which can be radically polymerized and which is
non-reactive under cationic polymerization conditions [71–73] . Generally, the
synthesis was based on the use of the functional initiator 30, which contains a
methacrylate ester group and a function able to initiate the cationic polymerization
of vinyl ethers. Such initiator can be obtained by the reaction of HI and the
corresponding vinyl ether. With initiator 30 the polymerization of ethyl vinyl
ether (EVE) was performed using I 2 as an activator in toluene at –40 °C. The MW
increased in direct proportion with conversion, and narrow MWD (M w/M n=
1.05–1.15) was obtained. The chain length could be controlled by the monomer
to initiator feed ratio. Three poly(EVE) macromonomers of different length
were prepared by this method: M n=1200, 5400, and 9700 g mol –1 . After complete