The Addition Polymerization of Cyclic Olefins

This extensive section deals with the late transition metal-catalyzed homopoiymerization of cyclic olefins to afford cycloaliphatic polymers, or saturated polymers in which the cyclic structure of the monomer remains intact in the polymer backbone. 

---

The Addition Polymerization of Cyclic Olefins 1105 Fig. 4.3 Brookhart catalyst for cyclopentene polymerization. 

The observation that the metal carbene complex, (CO)5W = C(Ph)2 [22], catalyzed the polymerization of cyclic olefins to ring opened polymers containing the diphenylmethylene unit of the catalyst provided additional evidence that carbenes were involved in the catalytic cycle. The formation of the initiating metal carbenes in the classic systems that consist of transition metal halides and alkylating agents was proposed to involve metal alkylation followed by oc-hydrogen loss, Eq. (6). Methane and propene were detected in the early stages of these reactions [23]. 

NMR studies of polymers made with deuterated monomers provide additional information on the cyclic isotactic transition state. Miyazawa and Ideyuchi (97) have shown that the isotactic polymerization of propylene takes place with cis opening of the olefinic double bond. This shows that the 4-membered cyclic transition occurs with reaction of the new monomer on the front side of the propagating ion as illustrated in Fig. 12. 

Not only polyethylene can be synthesized, but also many kinds of copolymers and elastomers, new structures of polypropylenes, polymers and copolymers of cyclic olefins. In addition, polymerization can be performed in the presence of fillers and oligomerization to optically active hydrocarbons is possible. For recent reviews and books see [17-20]. 

Using metallocene catalysts it has proved possible to tailor the microstructure of the polymers by fine-tuning of the ligands. Besides polyethylene, it is possible to co-polymerize ethylene with a-olefins such as propylene, but-l-ene, pent-l-ene, hex-l-ene, and oct-l-ene, in order to produce LLDPE. In addition, many kinds of co-polymers and elastomers, and new structures of polypropylenes, polymers and co-polymers of cyclic olefins can be obtained. Furthermore, catalysts with chiral centers can be beneficial in stereospecific polymerization to build the desired isotactic products. 

Various types of copolymers of cyclic olefins and other monomers have been prepared by asymmetric synthesis polymerizations using monomers with optically active side groups, ° optically active additives, " cata-lysts, or solvents.Among these, the synthesis of a copolymer of maleic anhydride and (S)-(-)-a-methylbenzyl methacrylate (MBMA, 269) is the first example of preparation of an optically active polymer consisting of a C-C backbone with chiral induction to the main chain. °... 

This unified volume explains the mechanistic basics of tactic polymerizations, beginning with an extensive survey of the most important classes of metallocene and post-metallocene catalysts used to make polypropylenes. It also focuses on tactic stereoblock and ethylene/propylene copolymers and catalyst active site models, followed by chapters discussing the structure of more stereochemically complex polymers and polymerizations that proceed via non-vinyl-addition mechanisms. Individual chapters thoroughly describe tactic polymerizations of a-olefins, styrene, dienes, acetylenes, lactides, epoxides, acrylates, and cyclic monomers, as well as cyclopolymerizations and ditactic structures, olefin/CO copolymers, and metathesis polyalkenamers. 

After Kaminsky, Brintzinger, and Ewen discovered homogeneous metallocene/ methylaluminoxane (MAO) catalysts for stereospecific a-olefin polymerizatiOTi (for reviews on olefin polymerization, see [13-21]), the first report [22, 23] rai addition cycloolefin polymerization without ROMP appeared. This stimulated a great interest in these polymers and in catalysts for cycloolefin polymerization (Fig. 1). Cycloolefins such as cyclopentene, cyclooctene, and norbomene can be polymerized via addition (Fig. 2). Polycycloolefins by metallocenes are difficult to process due to their high melting points and their low solubility in common organic solvents. However, metallocenes allow the synthesis of cyclic olefin copolymers (COC), especially of cyclopentene and norbomene with ethene or propene, which represent a new class of thermoplastic amorphous materials (Scheme 1) [24, 25]. 

The reaction of C—Li reagents with carbon-carbon double bonds has great technological relevance because it is the basis of the anionic polymerization processes. This reaction also affords convenient synthetic routes to cyclic compounds, when internal addition to an olefinic double bond present in the metallated molecule takes place (e.g. equations 68, 83 and 84). 

A wide variety of cyclic monomers have been successfully polymerized by the ring-opening process [Frisch and Reegan, 1969 Ivin and Saegusa, 1984 Saegusa and Goethals, 1977]. This includes cyclic amines, sulfides, olefins, cyclotriphosphazenes, and IV-carboxy-oc-amino acid anhydrides, in addition to those classes of monomers mentioned above. The ease of polymerization of a cyclic monomer depends on both thermodynamic and kinetic factors as previously discussed in Sec. 2-5. 

---