Transition Metal-Catalyzed Polymerization in Aqueous Systems - Late Transition Metal Polymerization Catalysis - page 235

Scheme 7.5 Aqueous cyclobutene polymerization by an insertion
mechanism (a) and by ring opening polymerization (b); SDS= sodium
dodecyl sulfate.
sions, they obtained a crystalline, highly stereoregular polymer (Scheme 7.5(a)) [28].
An insertion mechanism is evidenced by the intact ring structure of the polymer.
By contrast, in the presence of RuCl 3 as a catalyst precursor, ring opening poly-
merization of cyclobutene and 3-methylcyclobutene was observed exclusively
(Scheme 7.5(b)) [29]. With low efficiencies of ca. 15 TO, low-molecular-weight
stereoirregular oils were formed. Rinehart et al. have also reported ring opening
polymerization of norbornene and of 2-functionalized norborn-5-enes with polar
ester moieties in aqueous emulsion with moderate activities. Iridium(III) or Iri-
dium(IV) salts in combination with a reducing agent, or Ir I olefin complexes were
employed as catalyst precursors. Norbornadiene and dicyclopentadiene were also
polymerized, reacting with only one double bond [24, 30].
In summary, this pioneering work clearly demonstrated the possibility of aque-
ous catalytic insertion polymerization of acyclic and cyclic olefins, as well as aque-
ous ROMP. On the other hand, metal salts without any additional ligands to con-
trol the properties of the metal centers were utilized, and activation to the active
species was probably also relatively ineffective in most cases. Consequently, cata-
lyst efficiencies were moderate at best. Most of the polymerizations also afforded
low molecular weight materials, or employed rather special monomers. The possi-
bility of polymer latex synthesis appears not to have received much attention,
although free-radical emulsion polymerization of styrene and butadiene was al-
ready a large-scale process at the time.
7.2.2
Recent Progresses in Catalytic Insertion Polymerization of Olefins
Since the aforementioned investigations, significant advances in aqueous catalytic
insertion polymerization have only been made over the past decade. Alternating
copolymerization of olefins with carbon monoxide, polymerization of ethylene and
1-olefins, and polymerizations of norbornenes and of butadiene have been stud-
ied.