Norbornene copolymerization with ethene

Early transition metal catalysts such as vanadium complexes and zirconocenes effectively copolymerize ethene with norbornene [81]. This capabihty eventually led to the commercial development of the APEL and TOPAS line of cyclic olefin copolymers by Mitsui and Ticona (formerly Hoechst), respectively [82]. Interest in this class of polymers is due to its high glass transition temperatures and transparency that is imparted by the norbornene component. 

Kiesewetter, J. Kaminsky, W. Ethene/norbornene copolymerization with palladium(II) a-diimine catalysts. From ligand screening to discrete catalyst species. Chem. Eur. J. 2003, 9, 1750-1758. 

Norbornene can be copolymerized with olefins such as ethene and propene. Among these new COCs, made accessible from metallocenes, the ethene (E)-norbornene (N) copolymers are the most versatile and interesting ones (Figure 13, R=H). 

The highly controlled living copolymerization mechanism for E-N copolymerization with a PI catalyst/MAO is the result of the stabilization of an ethene-last-inserted species toward chain transfers. The coordination of highly nucleophilic and sterically encumbered norbornene to the ethene-last-inserted active species probably stabilizes the active species toward chain transfer and catalyst decay. Such a coordination would reduce the electrophilicity of the active site and, in addition, provide steric hindrance around the active site, which probably reduces all the possible chain transfers (e.g., hydrogen transfer to a reacting monomer, chain transfer to alkyl A1 species). Thus, the achievement of the controlled living copolymerization probably results from the stabilization of a Ti-E species toward chain transfers and its smooth change to a Ti-N species stable toward chain transfers. 

The scandium complex VIII-1 was used for the first time to achieve copolymerization of ethene with 5-norbornene-2-methanol and terpolymerization of ethene with norbornene and 5-norbomene-2-methanol with these highly sensitive family of catalysts. The requirements for the success were (1) the preactivation by [Ph3C][B(C6F5)4] and (2) the use of isolated APBus-protected monomer. Copolymers with high molar masses up to 330 000 gmol" ) and good incorpora-... 

Gmbbs introduced (salicylaldimino)nickel methyl com-plexes " that yield linear polyethene with high molar masses. These catalysts operate without requirement of a cocatalyst and allow the incorporation of bulky cycloolefins as norbornene as well as functionalities into polyethene. Copolymerization of ethene with norbornene in both nonaqueous " and aqueous solutions could be carried out by (salicylaldimino)nickel methyl complexes. 

Table 9 Ethene-norbornene copolymerization with Pd diimine catalysts [(2,6-Me2C6H3)2GLY]Pd (IX-1) and [(2,6-/-Pr2C6H3)2BUD]Pd (IX-2) ...

Figure 24 Palladium allyl complexes used for the copolymerization of norbornene or the functional derivatives N-C02Et, N-CH20C(0)Me, N-CH2OH, and N-COOMe with ethene.

DCPD, an inexpensive industrially available cyclic olefin, is a very promising and attractive monomer because it contains both a norbornene unit and a cyclopentene unit. If only one of the two double bonds in DCPD is selectively copolymerized with ethene, the remaining double bonds would be available for further functionalization. Nevertheless, the copolymerization of ethene with DCPD has not been extensively studied.A major problem often encountered in DCPD copolymerization appeared to be cross-linking, depending on concentration of comonomer and polymerization time. ... 

Conventional processes for preparing COCs have some common problems. The conversion of the cycloolefin may be low and further, a high amount of ethylene incorporated results in unsatisfactory low glass transition temperatures. Catalyst compositions have been developed in order to obtain materials with high glass transition temperatures (26). Examples are shown in Table 2.3. These catalysts are used for the copolymerization of ethene and norbornene. 

As a consequence of the living nature of the copolymerization wifh fhis catalyst, palladium-capped block copolymers of norbornene and ethene as well as of norbornene, ethene, and styrene were synthesized [61]. Higher activities (up to ten times higher) were observed for a series of oxazohne-phosphine complexes (e.g., 31). Several complexes, modified with bisphosphine monooxide and monosulfide ligands (Scheme 8.8, 32 and 33), were also used as catalysts precursors. The best reported turnover frequency is 0.6x10 mol (molh) at 80°C [62, 63]. A slightly lower activity was observed for fhe ketophosphine containing catalyst precursor 34 [64]. The activity of catalyst precursors 35, 36, and 37 is even lower [65]. 

In 1998, Grubbs [171,172] reported on a new type of neutral nickelll-complexes with salicylaldimin ligands (structure (31)). With these catalysts low branched polyethylenes were obtained with a narrow molecular weight distribution. The copolymerization of ethene and norbornene is possible. 

Copolymerization of ethene and norbornene with Me2C(Flu)(te/-t-BuCp)]ZrQ2 leads to a strong alternating structure [221]. This copolymer is crystalline and shows a melting point of 295 °C, good heat resistance and resistance against unpolar solvents. 

The processing of homopolynorbornene would be extremely difficult, due to a melting point higher than the decomposition, especially if the polymer is insoluble. Dimethanooctahydronaphthalene [DMON] is more rigid than norbornene. The copolymerization product of norbornene or DMON with ethene is amorphous, featuring high Tg values of 160 °C. The copolymers are insoluble in hydrocarbons and have an excellent transparency, thermal stability, and chemical resistance [555]. 

Compared to the CO insertion, fewer reports have appeared on the olefin insertion into an acyl palladium. Direct observation of this process has been reported very recently by Rix and Brookhart [89-92] using cationic l,10-phenanthroline-Pd(II) complexes. They have investigated the microscopic steps responsible for the alternating copolymerization of ethene with CO using the same 1,10-phenanthroline system. On the basis of the kinetic and thermodynamic data, they proposed an accurate model for the polymer chain growth. In support stepwise isolation of the intermediates have been accomplished by norbornene as a substrate where symmetrical bidentate nitrogen ligands were used [93-95]. 

Copolymerizations of ethene with bicyclic olefins, such as 2,5-norbornadiene, 5-vinyl-2-norbornene, have been investigated with metallocene catalysts. The secondary groups do not interfere with metallocene copolymerizations and post-polymerization functionalization makes it possible to synthesize functionalized polyolefins. 

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