Endblock compatible resins

Each Tg depends on the nature of that polymer segment itself and also on the nature of any materials dissolved in it. Figure 8 illustrates how the normal Tg of about 210°F for the end-block phase in an S-B-S polymer can be shifted by adding endblock compatible resins of differing softening points. 

The vapor permeability of thermoplastic rubbers with polydiene midblocks is similar to that of the rubber which forms the midblock. However, as the fraction of endblock is increased, as for example by adding endblock compatible resins, the permeability is somewhat reduced. Conversely, as the rubber phase fraction is increased, for example by adding a midblock compatible oil, the nitrogen permeability increases. While the permeability of thermoplastic rubbers is about the same as SBR, natural rubber, and poly butadiene, it is much higher than polyolefins and other materials used in packaging. This can be an advantage where high air or moisture vapor transmission is desired. 

Predominantly Endblock Compatible Resins. Poly aromatics, cumarone-indene resins,... 

Predominantly Midblock Compatible Resins. Aliphatic olefin derived resins, rosin esters, polyterpenes, and terpene phenolic resins derived from petroleum or terpentine sources and having relatively low solubility parameters tend to associate with the polydiene midblocks and not with the polystyrene endblocks. As the molecular weights or softening points of these resins are lowered, their solubility in the end-... 

---