Aliphatic polyalkenamers

The polyalkenamers are usually prepared by means of a Ziegler-Natta catalyst system. For example fran.v-polypentenamer may be obtained from cyclopentene 

Rubbery Cyclo-olefin (Cyclo-alkene) Polymers 305 

Because of side reactions which break the ring the ultimate polymers are more likely to be linear. 

As a class the aliphatic polyalkenamers have low values due to a combination of low chain stiffness and low interchain attraction. The presence of double bonds has the effect of increasing the flexibility of adjacent single bonds (see Chapter 4) and overall this leads to a reduction in. Thus in the sequence from polydecenamer down to polypentenamer an increase in the double bond concentration leads to a lowering of Tg. On the other hand the Tg of polybutenamer, i.e. poly butadiene, is somewhat higher than that of polypentenamer, presumably because the proportion of stiff links, i.e. double bonds, becomes sufficiently high to override the flexibilising effect on adjacent chains. Consequently the polypentenamers have the lowest Tg values known for hydrocarbon polymers (cis- -114°C, trans- -97°C). 

As a consequence considerable interest was shown in the trans-polypen-tenamer by Bayer as a potential general purpose rubber and particularly as a tyre rubber. In the event this hope did not materialise, apparently due to the following 

Rather more success has been achieved by trans-polyoctenamer, which was introduced by Hiils in 1980 under the name Vestenamer. The two initial grades had fran -contents of approx. 80 and approx. 62%. The polymers have a low molecular weight, and above the 7, which increases with increasing trans-content once the latter exceeds 30% and is about 60°C with the high transgrades, the polymer on its own has a very low melt viscosity. Below the melting 

---