Cyclopentene polymerization

Cyclopentene. After Eleuterio s early disclosure (10) of cyclopentene polymerization by ring-opening catalysis, Natta and co-workers (11) reported that trans polymer forms using WC16 catalyst and the cispolypentenamer forms using MoC15. The... 

Fig. 3. Effect of catalyst and conversion on microstructure for cyclopentene polymerizations (79, 80).

Fig. 4. Effect of temperature on microstructure and inherent viscosity for cyclopentene polymerizations (22).

Table III presents additional cyclopentene polymerization data with 1-pentene as a regulator at 0°C throughout a wide range of conversion. As long as the cis selectivity is maintained, the regulator remains inactive and does not participate in the scrambling process.

Cyclopentene polymerization has been catalyzed by several metallocenes (Table XVII). In each case, the homopolymers were found to contain no 1,2 enchainments. Whereas a mechanism similar to that proposed for the formation of 1,3 enchainments in polypropylene is reasonable, there is no plausible explanation for the formation of trans structures. 

Metathesis catalysts vary widely. They always contain a transition metal compound which is usually employed in combination with one or more cocatalysts like AlEt3. The most important catalysts for cyclopentene polymerization are derived from W or Mo. Low-molecular-weight alcohols are used in low concentrations to reduce the formation of oligomeric products. 

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

In the case of cyclopentene polymerization, the insertions at secondary alkyls are the only possible mode of chain growth no insertions adjacent to tertiary carbons are observed. For substituted cyclo-pentenes, there are more options in the polymerization. For instance, with 4-methylcyclopentene, insertion generally takes place on the unsubstituted side of the ring. This leaves a cis-C—H bond available for chain walking to the methyl group. The next insertion takes place at the primary carbon atom, giving a methylenecyclopentane polymer as illustrated in eq 8. A similar behavior is observed for... 

Early studies on cyclopentene polymerization with WCle-based catalysts [192] showed that the reaction kinetics correspond to a first-order equation. The following expression is found for the rate of monomer... 

In early studies of the molecular weight-regulating efficiency of various olefins in the metathesis polymerization of cyclopentene, the results of... 

Polymerization of Cyclopentene in the Presence of 2-Pentene by WF6/C2H5A1C12 Catalyst"... 

For the n = 5 case there is the unique starting material of cyclopentene (16, n = 5) and polymerization enthalpy16 from which the enthalpy of formation of [—CH=CH—(CH2)3— ] is found to be —14 kJmol-1. The enthalpy of hydrogenation is thus ca —121 kJmol-1. Likewise, for n = 6, 7 and 8, the respective enthalpies of hydrogenation of [—CH=CH—(CH2)n-2] are seen to be ca —83, —120 and — 121 kJmol-1. Except for the n = 6 case, the various enthalpies of hydrogenation are around —120 kJmol-1, a value comparable to those found for numerous simple internal olefins reported in References 11 and 14. We can think of no reason why the n = 6 case should be so different from the others17. 

As expected, the metathesis polymerization of more strained cycloalkenes, such as cyclobutene, occurs more rapidly than less strained structures such as cyclopentene. 

Polymers containing rings incorporated into the main chain (e.g., by double-bond polymerization of a cycloalkene) are also capable of exhibiting stereoisomerism. Such polymers possess two stereocenters—the two atoms at which the polymer chain enters and leaves each ring. Thus the polymerization of cyclopentene to polycyclopentene [IUPAC poly(cyclopen-tane-l,2-diyl)] is considered in the same manner as that of a 1,2-disubstituted ethylene. The... 

Cyclopentene yields mixtures of ROMP and double-bond polymerization with some Ti and V initiators. ROMP occurs exclusively with molybdenum and tungsten initiators, as well as Re, Nb, and Ta initiators. The relative amounts of cis and trans structures vary with the initiator and temperature [Dall Asta et al., 1962 Pampus and Lehnert, 1974]. Metallocene initiators polymerize cyclopentene through the double bond, but the polymer structure consists of cis 1,3-placement (Coates, 2000 Kaminsky, 2001 Kelly et al., 1997]. 

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