Olefins copolymerization with norbornene

With the discovery of ruthenium carbene complexes as highly effective catalysts for olefin metathesis under mild reaction conditions [233,234], the scope of ring-opening metathesis polymerization could be extended to include functionalized and sensitive monomers. The resulting (soluble) polymers have been used as supports for simple synthetic transformations [235-237]. Insoluble polymers have been prepared by ringopening metathesis copolymerization of norbornene with l,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene. These polymers have been used as supports for ruthenium carbene complexes [238]. 

There are three different mechanisms by which the cyclic olefin norbornene can be polymerized to reasonably high molecular weights ring-opening metathesis polymerization (or ROMP), vinyl addition copolymerization with acyclic olefins such as ethylene, and vinyl addition homopolymerization (see Fig. 4.2). Carbocationic and free-radical initiated polymerizations are ignored since they yield only low molecular weight oligomers [8]. 

The addition copolymerization of norbornene-type monomers with a-olefins [21] forms the basis of EPDM (ethylene propylene diene monomer) technology. Incorporation of smaU amounts of DCPD or ethylidene norbornene (ENB) in olefinic vinyl addition polymers provides latent crosslink sites in EPDM elastomers. It is weU known in the hterature that incorporation of higher amounts of rigid, bulky multicychc olefins results in materials with higher TgS [22]. In fact, more recent work has concentrated on increasing the Tg of norbornene-type monomer/a-olefin copolymers [23]. The use of late transition metal catalysts to prepare such copolymers is reviewed in Section 4.3. 

A first glance at Fig. 4.11 suggests that the effect of olefins on polymer MW is catastrophic, since at 30 mol% 1-decene the products are in the trimer-hexamer range (M,< 1000) however, further study revealed that the control of MW is very precise and controllable. Indeed, the addition of controlled levels of 1-decene (or other a-ole-fins) proved to be a very reproducible way to achieve any desired MW from ohgo-mers up to very high MW polymers. This is illustrated in Fig. 4.12, where it can be seen how precisely the molecular weight can be controlled, and that similar molecular weights result whether the studied polymerization is a homopoiymerization of norbornene itself or a copolymerization with alkylnorbornenes. 

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. 

Material properties of olefin metathesis polymers made by thermal (ROMP) or photoinduced (PROMP) polymerization with ruthenium (Il)-salts and the later developed ruthenium-phosphines as catalysts are described. The low oxidative stability was improved by copolymerization with so-called "build-in" antioxidants (AOs), i.e. hindered phenols or aromatic amines bearing 2-norbornene units. 

Additionally, certain internal olefins can be copolymerized with CO, albeit at much reduced rates. For example, by employing 2-butene, low molecular weight oligomers of poly( 1,5-ketone) are obtained by a sequence of insertion and isomerization steps (54). Copolymers with strained internal olefins such as (functionalized) norbornene or norbornadiene can also be made (55). 

Norbomene can be copolymerized with olefins such as ethylene, propylene, 1-butene, and longer-chain a-olefins using early and late transition metal catalysts. The resultant copolymer properties depend on different parameters, such as comonomer content and distribution throughout the polymer chain, as well as the conformational orientation of the comonomer units. The microstmcture of the copolymer can be controlled by the appropriate choice of reaction conditions and catalyst stmcture. The most powerful method to determine copolymer microstmcture is NMR spectroscopy. In the past years, much progress has been achieved in making peak assignments for olefin-norbornene copolymers. - ... 

The first examples involving homo- or copolymerization of olefins (e.g., norbornene) bearing a ferrocenyl substituent were performed using Mo-based initiators by Schrock and coworkers [3] (Scheme 12.1a). Depending on the reaction conditions and monomer(s) ratio, redox-active polymers or block copolymers were obtained with narrow polydyspersities. Solution measurements showed that the redox centers in homo- and copolymers were electrochemically independent. 

Metallocene catalysts have a unique feature of polymerizing cyclo-olefin monomers (i.e., cyclopentene, norbornene) selectively without ring opening, and also enable copolymerization with ethylene [47, 48]. Application of metallocene catalysts to cyclo-olefin copolymer (COC) will be discussed in Section IV. 

Shiono and coworkers also reported the living copolymerization of propylene and norbornene with 5/dMAO to produce copolymers with very high Tg values (249 °C) and narrow molecular-weight distributions MJM =. 6) (Hasan et al, 2005). In a later report, the copolymerization of higher a-olefins (1-hexene, 1-octene, and 1-decene) with norbornene by 5/MAO was reported, however, molecular-weight distributions were somewhat broadened (M /Mn= 1.36-1.72) (Shiono et al, 2008). 

A solution to the steric bulk of the macromonomers is grafting from where polymerizations occur from the functionalized side chains of the ROMP-generated backbone. The copolymerization of propylene with 4mol% GOD yielded terminal vinyl groups off the main polymer chain resulting from the addition of the GOD. Attachment of the catalyst at the vinyl group via olefin metathesis enabled ROMP of nor-bomene derivatives from the polyolefin backbone.In a grafting from approach, norbornene monomers with covalently attached ATRP initiators were copolymerized with ester-functionalized norbomenes to form the polymeric backbone. The ATRP of acrylic acid successfully yielded the brush polymer. 

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). 

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. ... 

Organolanthanide complexes can catalyze not only the homopolymerization of ethylene, but also the copolymerization of ethylene with some nonpolar and polar monomers [139, 140], A series of neutral, anionic, and cationic organolanthanide complexes catalyze the copolymerization of ethylene with styrene, a-olefins, methylenecyclopropane, norbornene,... 

Two classes of diene have been copolymerized successfully with ethylene/propene, in both of which one double bond is deactivated such that the monomer behaves as a mono-olefin. These are unconjugated diolefins, such as cis and trans 1,4-hexadiene or 3,7-dimethyl 1,6-octa-diene, and compounds containing the 2-norbornene structure... 

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]. 

In addition to linear a-olefins, Shino and coworkers reported that 5/MAO catalyzed the living copolymerization of ethylene and norbornene. At 0 °C, 5/MAO can furnish poly(E-co-NB) with 53 mol% norbornene and M = 18 000 g/mol with MJM =1.16 (Hasan et al, 2004b). In addition, a linear increase in with reaction time was observed for this system. At 40 °C, a similar compound, lO/MAO, also provided ethylene-norbomene copolymers with fairly narrow PDls MJM =. 2 -. 21) (Hasan et al, 2004a). 

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. 

For many years Ziegler-Natta coordination copolymerization of ethylene with propylene and non-conjugated dienes (such as hexa-1,4-diene and 5-ethylidene-2-norbornene) has been used to prepare an important class of rubbers known collectively as EPDM rubbers. More recently, copolymerization of ethylene with small proportions of higher a-olefins (such as but-l-ene, hex-l-ene and oct-l-ene) has become important and is used to prepare a range of copolymers known as linear low-density polyethylenes (LLDPE). 

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