5-Methyl-1-heptene, polymerization

The failure in separating in fractions possessing optical activity of opposite sign the stereoregular polymers of racemic 5-methyl-l-heptene, polymerized in the presence of the same catalyst as that used to prepare polymers from racemic 3-methyl-l-pentene and 4-methyl-1-hexene (75), might be an indication that, in order to obtain prevailingly (R) and (S) separable polymers instead of random copolymers from racemic vinyl monomers, the asymmetric carbon atom of the monomer must be in a or in / position with respect to the double bond. 

Such a-olefins as (+)- S)-3-methyl-l-pentene, (—)(S)-4-(methyl-l-hexene, and (+ )(S)-5-methyl-heptene have been polymerized with a titanium trichlo-ride/tri-isobutylaluminum catalyst without solvents. From the product mix, by solvent extraction crystalline and amorphous fractions were isolated. Both forms... 

Studies on stereoselective polymerization of racemic olefins also support this view.338 Polymerization of 3,7-dimethyl-l-octene (the chiral center is in a position to the double bond) took place with 90% stereoselectivity yielding an equimolar mixture of homopolymers of the two enantiomers. No stereoselectivity was observed in the polymerization of 5-methyl-1-heptene (the chiral center is in y position to the double bond). The conclusion is that the ability of a catalytic center to distinguish between the two enantiomers of a monomer required for stereoselective polymerization must arise from its intrinsic asymmetry. The first-ever chiral polypropylene synthesized using a chiral zirconium complex with aluminox-ane cocatalyst is the latest evidence to testify the role of the catalyst center in isotactic polymerization.339... 

Under similar conditions, the 2-methylenebicyclo[2.2.1]heptane, or norcamphene (7) was conYerted to the isomer 6, through the intermediate formation of 5, whose maximum concentration in the mixtures is about 10%. This slow reaction is complicated by extensive hydrogen transfer and polymerization reactions (20), leading to saturated bicyclic hydrocarbons 2-methylbicyclo[2.2.1]heptane (12), bicyclo[3.2.1]- and [3.3.0]octanes (15 and 17). Isomerization of norcamphene (7) to hydrocarbons of the bicyclo[2.2.1]heptane series is also noticed at 250° in the vapor phase, but this is the main reaction at 140° in the liquid phase with the same catalyst. The main products are then 2-methyl-bicyclo[2.2.1]-2-heptene (8), l-methylbicydo[2.2.1]-2-heptene (10), and l-methyltricyclo[2.2.1.0]heptane 11 (13). The tricyclic isomer has been observed in the liquid-phase silica-alumina-catalyzed conversion of norbornene (21). 

Propylene has been co-polymerized with a broad set of higher olefins to isotactic co-polymers, including 1-pen-tene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene,... 

Other monomers that undergo isomerization polymerization include 5-methyl-l-hexene, 4,4-dimethyl-1-pentene, 6-methyl-l-heptene, a-pinene, and vinylcyclopropane. 

In addition to propylene, other nonconjugated olefins have been copolymerized with CO using enantiopure palladium catalysts. Allylbenzene, 1-butene, 1-heptene, 4-methyl-l-pentene, and cis-2-butene [84,85] as well as hydroxy- and carboxylic acid-functionalized monomers [87] have been polymerized to give optically active polymers. Waymouth, Takaya and Nozaki have recently reported the enantioselective cyclocopolymerization of 1,5-hexadiene and CO [88,89]. 

The development of bifunctional catalysts for specific catalytic sequences of reactions in which the product of the first reaction can serve as substrate for the second is of great importance. There are many examples of such reactions. They are, for instance, the monomer-isomerizing polymerization of heptene-2, heptene-3 and 4-methyl-2-pentene and the combination of propene disproportionation with oligomerization, etc. Bifunctional catalysts are most widely used for ethylene copolymerization with a-butene in situ in the production of so-called low-density linear polyethylene (LDLPE). All general methods for LDLPE production are based on incorporation into a PE backbone of short-chain branches, which can be made by catalytic copolymerization of ethylene with a-olefins C3-C10. A macromolecnlar ligand offers wide possibilities of joining the different types of active site in the same matrix (see also Section 12.5.2). 

Polymerizations of many internal olefins, like 2-butene, 2-pentene, 3-heptene, 4-methyl-2-pen-tene, 4-phenyl-2-butene, and others, with Ziegler-Natta catalysts, are accompanied by monomer rearrangements. The isomerizations take place before insertions into the chains. The double bonds migrate from the internal to the a-positions ... 

Cyclohexene-l-one, methyl vinyl ketone, phenylacetylene, diphenylacety-lene, benzaldehyde, perfluoro-l-heptene, and cyclohexene were found to not be effective dienophiles for the reaction. Only polymeric o-xylylene products were seen in the reaction mixture. In addition, no cycloadduct was produced by using / -benzoquinone as the dienophile. Only hydroquinone and a,a -diiodo-o-xylene were recovered. The hydroquinone presumably results from the reduction of benzoquinone by nickel. Since sodium iodide is known to react with dibromo-o-xylene to give diiodo-o-xylene [112], the diiodo-o-xylene could result from the reaction of unconsumed dibromo-o-xylene with lithium iodide which is present in the reaction flask. These results are analogous to those reported in a similar reaction by Scheffer [113], where the use of zinc metal and ultrasound gave only hydroquinone and a quantitative yield of the unreacted dibromo-o-xylene. 

The first experiments in this field, on racemic a-olefins, appeared in 1955 when crystalline isotactic polymers issued from racemic 4-methyl-1-hexene were described by Natta etal [161a]. Several racemic a-olefins 3-methyl-l-pentene (a), 4-methyl-1-hexene (b), 5-methyl-1-heptene (c), and 3,7-dimethyl-l-octene (d) were polymerized by a catalytic... 

This contrasts with the results published by Chiellini etal [173] about stereoregular copolymers of racemic 5-methyl-1-heptene with OA 2-methylbutylvinylether. From adsorption chromatography data on poly(L)-lactide which leads to optically inactive fractions, it seems doubtless that the polymerization is stereoselective, even if at least partially isospecific that means able to give prevailingly isotactic polymers. 

Fig. 2. Molar optical rotation [(0] f) ) vs polymerized monomer optical purity of isotactic vinyl polymers having the asymmetric carbon atom in the 7 position to the main chain. -O- poly-[(/J)-o -phenylethyl]-methacrylate -C- poly-(+)-menthylmethacrylate poly-(5 )-5-methyl-l-heptene poly-[(5 )-2-methylbutyl]-vinyl ether.

---