Dear researchers,
Would you please tell me: at which pH polyepoxysuccinic acid and polyaspartic acid fully dissociate in water? I mean what are their pk values?
Thanks.
Polyacids and/or polybases do not have a single pKa value. Depending on the conjugation of acid/base moities you will get multiple pka values or better said a broad range of protonation states. For instance, the pKa of allyl amine is 9.5, however, when it is polymerized to produce poly allylamine the pKa is not 9.5, A quote from the following paper may aid in your understanding
"That is, the buffer region of the titration curve is spread out over several pH units. Also, the apparent pKa of the polymer, defined as the point at which half of the amine groups are protonated, is 8.7. This is 2.1 pH units lower than the typical pKa of an aliphatic amine, which is ∼10.8. The lower pKa reflects the fact that cation-cation repulsion in the polymer makes it progressively more difficult to protonate as the mole fraction of protonated amine groups increases. At pH 10.8, only about 2% of the amine groups in the polymer are protonated. At the monomer pKa, therefore, one would not expect strong interactions between PAH and polyanion sheets."
http://research.chem.psu.edu/mallouk/articles/cm981066k.pdf
Additionally, a titration curve for a polymer looks very different from a titration curve of a small molecule as can be seen in the mentioned paper.
Polyacids and/or polybases do not have a single pKa value. Depending on the conjugation of acid/base moities you will get multiple pka values or better said a broad range of protonation states. For instance, the pKa of allyl amine is 9.5, however, when it is polymerized to produce poly allylamine the pKa is not 9.5, A quote from the following paper may aid in your understanding
"That is, the buffer region of the titration curve is spread out over several pH units. Also, the apparent pKa of the polymer, defined as the point at which half of the amine groups are protonated, is 8.7. This is 2.1 pH units lower than the typical pKa of an aliphatic amine, which is ∼10.8. The lower pKa reflects the fact that cation-cation repulsion in the polymer makes it progressively more difficult to protonate as the mole fraction of protonated amine groups increases. At pH 10.8, only about 2% of the amine groups in the polymer are protonated. At the monomer pKa, therefore, one would not expect strong interactions between PAH and polyanion sheets."
http://research.chem.psu.edu/mallouk/articles/cm981066k.pdf
Additionally, a titration curve for a polymer looks very different from a titration curve of a small molecule as can be seen in the mentioned paper.
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