Cycloaliphatic Polymers via Late Transition Metal Catalysis - Late Transition Metal Polymerization Catalysis - page 104

Fig. 4.3 Brookhart catalyst for cyclopentene polymerization.

4.2.3
Norbornenes

The addition copolymerization of norbornene-type monomers with -olefins [21]

forms the basis of EPDM ( e thylene p ropylene d iene m onomer) technology. Incor-
poration of small amounts of DCPD or ethylidene norbornene (ENB) in olefinic
vinyl addition polymers provides latent crosslink sites in EPDM elastomers. It is
well known in the literature that incorporation of higher amounts of rigid, bulky
multicyclic olefins results in materials with higher T g s [22]. In fact, more recent
work has concentrated on increasing the T g of norbornene-type monomer/ -olefin

copolymers [23]. The use of late transition metal catalysts to prepare such copoly-
mers is reviewed in Section 4.3.
The vinyl addition homopolymerization of norbornene, resulting in poly(2,3-
norbornene) was first mentioned in the early 1960s using classical TiCl 4 -based
Ziegler systems [24]. These catalysts afforded only very low molecular weight
materials (molecular weights <1000) at low yields. Zirconocene/methaluminoxane
systems are reported to afford high polymers, but these polymers decompose in
air at high temperatures before they melt and are insoluble in organic solvents
[25]. Furthermore, for the homopolymerization of norbornene zirconocene addi-
tion catalysts exhibit low activity and require the use of a large excess of expensive
methaluminoxane (MAO). Electrophilic palladium(II) complexes effect the “living”
polymerization of norbornene [26, 27]. For example, cationic palladium complexes
such as [Pd(CH 3 CN) 4 ][BF 4 ] 2 , in solvents such as nitromethane, were found to
homopolymerize norbornene to high polymers with reasonable solubility in sol-
vents such as tetrachloroethylene, chlorobenzene and o -dichlorobenzene. These
polymers exhibit molecular weights in excess of 100000 and also were found to
have high glass transition temperatures ( T g >300

C). Three brief reviews of the vi-
nyl polymerization of norbornene have recently appeared [28].
Thus, until the last decade, three families of catalysts have been reported to cat-
alyze the addition, or “vinyl-type” homopolymerization of norbornene resulting in
poly(2,3-bicyclo[2.2.1]hept-2-ene). These three catalyst types are the classical TiCl 4 -
based Ziegler systems (type 1), the zirconocene/aluminoxane systems (type 2) and
certain electrophilic palladium(II) complexes (type 3).
The homopolymerization of norbornene is described in a process patent to Ide-
mitsu Kosan [29]. This patent application describes the use of catalysts compris-