Cyclopentene addition polymerization

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

Metallocene/methylaluminoxane (MAO) and other single site catalysts for olefin polymerization have opened a new field of synlhesis in polymer chemistry. Strained cyclic olefins such as cyclobutene, cyclopentene, norbornene (NB), and their substituted compounds can be used as monomers and comonomers in a wide variety of polymers." Much interest is focused on norbornene homo- and copolymers because of the easy availability of norbornene and the special properties of their polymers. Norbornene can be polymerized by ring opening metathesis polymerization (ROMP), giving elastomeric materials, or by double bond opening (addition polymerization). Homopolymerization of norbornene by double bond opening can be achieved by early and late transition metal catalysts, namely Ti, Zr, Hf, Ni, - ° and Pd (Scheme 16.1). 

Cyclopentene has been polymerized in the presence of numerous catalytic systems leading either to poly(ey-clopentenylene) by addition polymerization or to poly-pentenylene or polypentenamer by ring-opening metathesis polymerization. Thus, in an early report, Hoffman [54] observed that the oUgomerization of cyclopentene in the presence of BF3/HF proceeded to dimers, trimers, and tetramers as well as to solid resins. The structure probably corresponded to a 1,2-addition polymer, poly(l,2-cyclopentenylene) [Eq. (10)]. 

Figure 1 Microstructures of poly(cyclopentenes) obtained by double bond opening (addition polymerization).

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.

It is generally agreed that alkenyl hydroperoxides are primary products in the liquid-phase oxidation of olefins. Kamneva and Panfilova (8) believe the dimeric and trimeric dialkyl peroxides they obtained from the oxidation of cyclohexene at 35° to 40° to be secondary products resulting from cyclohexene hydroperoxide. But Van Sickle and co-workers (20) report that, The abstraction/addition ratio is nearly independent of temperature in oxidation of isobutylene and cycloheptene and of solvent changes in oxidations of cyclopentene, tetramethylethylene, and cyclooctene. They interpret these results to support a branching mechanism which gives rise to alkenyl hydroperoxide and polymeric dialkyl peroxide, both as primary oxidation products. This interpretation has been well accepted (7, 13). Brill s (4) and our results show that acyclic alkenyl hydroperoxides decompose extensively at temperatures above 100°C. to complicate the reaction kinetics and mechanistic interpretations. A simplified reaction scheme is outlined below. 

Butadiene. The reaction of methylene with butadiene was studied by Frey44 under experimental conditions similar to those in the case of allene, except that lower pressures were required to avoid butadiene polymerization. Products formed by attack of methylene on the C—H bonds were cis and vinyl-cyclopropane resulting from addition of CH2 to the carbon-carbon double bond underwent collisional deactivation or isomerization to cyclopentene and C dienes, with the exception of isoprene. 

Group 4 metallocene catalysts are, in addition to polyethylene and polypropylene, able to generate syndiotactic polystyrene, to polymerize cycloolefins (cyclopentene, nor-bomene, and their substituted compounds), and to give access to various copolymers. During the polymerization of cycloolefins, only the double bond is opened and not the ring. 

In addition to the above mentioned processes realized in industrial scale, many other applications, (e.g., the (co-)polymerization of cyclopentene [1] or cyanonorbornene... 

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]. 

Copolymers of cyclopentene (Cyp) with alkyltrimethylsilane (ASi) were synthesized in addition to the ones of cyclopentene with ethene ) that were described previously. It could be assumed that the bilky silyl side groups in combination with the cyclopenten unit would promote optical rotation. The S enantiomeric form of Et(lndH4)2ZrCl2 was used as an optically active catalyst. Table 5 shows the polymerization conditions. 

The maximum in the polymerization rate curves for isobutyl vinyl ether,2-phenylvinyl alkyl ethers, 1-octene, norbornene/ " vinyl acetate,butene isomers,and cyclopentene copolymerizations with MA are located somewhat outside the 1 1 feed ratios. Even though 1 1 copolymer is obtained, the maximum rate of styrene-MA copolymerization is normally not at 1 1 feed equivalency. However, Tsuchida and Tomono show that addition of naphthalene causes the rate maximum point to shift... 

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