Properties of Styrenic Block Copolymer Elastomers

Albert Einstein said that it is good to make things as simple as possible, but not simpler. Beneath each simple statement about the properties of styrene block copolymers lie volumes of books, thousands of patents and countless pages of paper and electronic files dedicated to describing and understanding these highly useful polymers, and their applications. The task becomes reducing all of this to simple ideas, simple pictures and simple words, but not simpler . 

One simple idea is that styrenic block copolymers are almost never used as a stand-alone 100% neat polymer for any application or use. We tend to think about polymers in terms of this plastic soda bottle is polyester, or this carpet fiber is polyamide, or this house siding is PVC, or this garbage bag film is polyethylene , fully understanding and meaning that virtually 100% of the named object is that polymer. Our brains usefully process the named polymer properties set (as neat polymer) into the desired and required property set for its application. Life is simple in the 100% world. It is intuitive, and what we seem to know makes sense, looking either way properties wise, to why this polymer is used for this application. 

we can begin to take a look at some what ifs . What if the styrene content is much higher than data point A What if the endblock size is much smaller than A What if the molecular weight is much less than or much greater than A Are there boundaries, and what is their nature  

If we look at Table 21.1 [64], we can see that there is a lower limit to how small a styrene endblock can be in a styrene-isoprene-styrene (SIS) styrenic block copolymer before the strength is severely reduced, or is reduced to that of chewing gum. There is a lower minimum molecular weight for the styrene block that will not yield a useful polymer or property set, let alone an elastomer. Thus, we have a lower boundary condition on how small the endblock is allowed to be. Similar results are found for styrene-butadiene-styrene (SBS) block copolymers [65]. 

The left panel is an example of a higher molecular weight version of a hydrogenated block copolymer with the same chemical structure as in the 

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