Comparatively Speaking: The Meaning of Subscripts

By: Anthony J. O'Lenick, Jr., Siltech LLC

Posted: March 11, 2009

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The reason for this is two-fold. First, the exact location of a particular ethylene oxide segment or propylene oxide segment on a backbone in a complex mixture is an analytical nightmare to determine. Second, even if it were possible, there would be an endless number of names for these polymers depending on their exact structure.

Assume the EO and PO were mixed then added to the alcohol, and assume there is no difference in reactivity between EO and PO, which is a faulty assumption. If a = 1 and b = 1, then Figures 2 and 3 show the two possible products.

As the chemists moves to a = 2 and b = 2, things get complicated there are now more possible products:

Sequence     Order
1                      ABAB
2                      BABA
3                      AABB
4                      BBAA

The possibilities then grow exponentially as the number of “a” and “b” are added.