Polybutadienes macrostructure

The information on physical properties of radiation cross-linking of polybutadiene rubber and butadiene copolymers was obtained in a fashion similar to that for NR, namely, by stress-strain measurements. From Table 5.6, it is evident that the dose required for a full cure of these elastomers is lower than that for natural rubber. The addition of prorads allows further reduction of the cure dose with the actual value depending on the microstructure and macrostructure of the polymer and also on the type and concentration of the compounding ingredients, such as oils, processing aids, and antioxidants in the compound. For example, solution-polymerized polybutadiene rubber usually requires lower doses than emulsion-polymerized rubber because it contains smaller amount of impurities than the latter. Since the yield of scission G(S) is relatively small, particularly when oxygen is excluded, tensile... 

Table 9.12 shows how polybutadiene microstructure and macrostructure (i.e., molecular weight, Mw, Mn, polydispersity, and branching) can affect the processability of a polymer (Kumar et al 1996). A study with both cobalt- and neodenium-catalyzed polybutadiene showed the relationship between polydispersity or molecular weight distribution and increases in stress relaxation. Increases in stress relaxation, as measured by the Mooney viscometer, will infer greater difficulty in compound processing, gauge control, nerve, and extrudate or calendered sheet shrinkage (Waddell et al 2004). 

Anionic Polymerization. Complementing the diversity in microstructure inherent to anionic chemistry, living anionic polymerization based on alkali metal alkyl initiating systems can also afford a wide range of macrostructural possibilities for polybutadiene products. 

Medium and High Vinyl Polybutadiene. Many tire performance properties are closely related to the glass-transition temperature of the polymer system used (324,325,346). As the glass-transition temperature is increased, wet and dry traction is increased, but abrasion resistance is compromised (347). Again, hysteretic properties are more a ftmetion of macrostructure than glass-transition temperature. Figure 4 depicts the trends in tire performance properties as a function of polybutadiene vinyl content (271). 

---