Dicumyl peroxide cross-linked polybutadiene

Figure 8.29 plotted against Gg for three rubbers [polybutadiene (PB), styrene-butadiene copolymer (SBR), and natural rubber (NR)] at different stages of cross-linking by (O) dicumyl peroxide and ( ) sulfur. (From Ref. 44.)... 

Polybutadiene is readily cross-linked by heating with 1% dicumyl peroxide for 10 min at 145°C. If the product is first extracted with C2CI4 to remove any non-cross-linked material and then placed in eontact with WCl6/EtA.lCl2/EtOH in C2CI4 at 45°C, it rapidly goes into solution (Hummel 1970 Kumar 1981). An added acyclic olefin assists this process but is not essential. It is clear that the network can be readily broken down by the occurrence of either intramolecular or intermolecular metathesis reactions. 

Figure 19. Proposed cross-linked structure of cis-polybutadiene vulcanized with dicumyl peroxide.

Filled elastomers - polybutadiene containing small untreated glass beads 30 - 95 /xm in diameter, 0 - 34% by volume, cross-linked with dicumyl peroxide. We also examine the peeling detachment of polybutadiene bonded to a macroscopic flat glass surface. 

FIG. 14-1. Logarithmic plots of G against radian frequency at 25 C for four cross-linked polymers showing the onset of the transition zone. (NR) natural rubber (PB) 1,4-polybutadiene, about 50% trans (SBR) styrene-butadiene rubber with 23.5% styrene (Butyl) butyl rubber. All cross-linked with sulfur except SBR by dicumyl peroxide. (A) Plotted directly (B) with scales shifted to make C, and to, coincide with the values for natural rubber (indicated by cross). Reproduced by permission, from Science and Technology of Rubber, edited by F. R. Eirich, Academic Press, New York, 1978. 

The polydienes consist of films cured with dicumyl peroxide. These cross-linked samples were swollen with a solution of the probe in cyclohexane and dried by extensive pumping in vacuo. Films with raw polybutadiene were also prepared by casting onto a quartz plate a cyclohexane solution containing the probe. 

---