Friday, June 15, 2007

PVA - Err, is that alcohol or acetate?

Continuing on the theme of confusing polymer names, this week’s subject is “PVA”.


The “PV” is easy: “Polyvinyl-“.  The problem with this TLA (“three-letter acronym”) is that the “A” could be either “alcohol” or “acetate” (or actually both, since copolymers of these two are trivial to prepare.)  It could also stand for “acrylamide”, although that is pretty uncommon, and usually goes by “Am”.  Kind, gentile authors will use “PVAc” for the acetate, but that still is not a common enough that you can assume it will ALWAYS been indicated as such.


PVA is unusual for a "vinyl" polymer in that it is not made by polymerizing "vinyl alcohol".  Vinyl alcohol doesn't exist.  Anytime you do try and make it, it undergoes a keto-enol rearrangement to form acetaldehyde.  (If you didn't know that, don't feel bad.  Linus Pauling forgot about keto-enol rearrangements and consequently was wrong when he published his version of the structure of DNA.  Too bad, as that would have yielded a THIRD Nobel Prize for the guy.  Instead he just had to be happy with 2 Nobel Prizes.)


Anyway, PVA starts off as PVA which then undergoes a reaction to form PVA.  Confused?  Let me restate this.  Polyvinyl alcohol starts off as polyvinyl acetate which then undergoes a (hydrolysis) reaction to form polyvinyl alcohol.  By varying the degrees of hydrolysis, you can end up with either straight polyvinyl alcohol or polyvinyl (acetate-co-alcohol). 

1 comment:

Gaussling said...

I did some work making custom colloidal dispersions based on polyvinyl acetate. We were making specicalized inks.