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PGA/PLA/PLGA polyesters

  1. Jun 30, 2010 #1
    Esters have the form R-CO-OR'.

    PGA has the form [-O-CH3-CO-].
    It is a polyester that means an ester according to Wikipedia.
    I cannot see why it is an ester.
    It does not have two oxygens bind to one carbon.

    Why is PGA an ester?
     
  2. jcsd
  3. Jun 30, 2010 #2

    chemisttree

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    No it doesn't. Review that part again.
     
  4. Jun 30, 2010 #3
    The form of the ester is right: http://en.wikipedia.org/wiki/Ester

    One part of PGA has the above form.
    I had only the given part of PGA in the exam. It was my first time to see PGA.

    I am trying to deduce somehow that PGA has an ester -part.
    PGA is poly glycosidic acid.
    This means that there is a glycosidic bond in the polymer, probably many.
    Glycosidic bond is within an ester: http://en.wikipedia.org/wiki/Glycosidic_bond

    Does an ester have always a glucosidic bond?

    It seems that the key to solve the problem was to think about the abbreviations of PGA, not the single unit of the polymer.
     
  5. Jun 30, 2010 #4

    chemisttree

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    5 bonds to carbon. It's wrong.

    You gave a general formula for an ester as R-CO-OR' but you chose to show it in a different way for the polymer. Does this help?

    PGA (polyglycolic acid) = [-CH2-COO-]
    which is equivalent to [-OCH2-CO-]
     
  6. Jul 1, 2010 #5
    WOOT!
    Thank you!
    I did not get it that it is the monomer of the PGA.
    It seems that PGA does not have different monomers: only the one.

    I now see that the monomer really make the polymer an ester.
     
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