Polyaspartic acid

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Polyaspartic acid
Names
Other names
PASP
Identifiers
ChemSpider
  • none
Properties
(C4H5NO3)n
Molar mass variable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Sodium polyaspartate

Polyaspartic acid (PASA) is a

water-soluble condensation polymer based on the amino acid aspartic acid.[1][2] It is a biodegradable replacement for water softeners and related applications.[3] PASA can be chemically crosslinked with a wide variety of methods to yield PASA hydrogels.[4] The resulting hydrogels are pH-sensitive such that under acidic conditions, they shrink, while the swelling capacity increases under alkaline conditions.[4]

Sodium polyaspartate is a sodium salt of polyaspartic acid.

In nature, PASA has been found in as fragments of larger

polycondensation of aspartic acid, was reported by Hugo Schiff in late 19th century.[7] Later it was proposed that thermal polymerization process leads through polysuccinimide intermediate.[8][9] Polyaspartic acid is produced industrially in both the acid form and as the sodium salt.[2]

Properties and structure

Due to presence of

biodegradability.[2]

Synthesis

Some synthetic strategies leading to polyaspartic acid
Some synthetic strategies leading to polyaspartic acid
Isomers of PASA repeating unit

Many different routes lead to PASA. In the simplest[10] and the oldest approach[6] aspartic acid is heated to induce dehydration. In a subsequent step the resulting polysuccinimide is treated with aqueous sodium hydroxide, which yields partial opening of the succinimide rings. In this process sodium-DL-(α,β)-poly(aspartate) with 30% α-linkages and 70% β-linkages[11] randomly distributed along the polymer chain,[12] and racemized chiral center of aspartic acid is produced.[13] There were many catalysts reported for improving thermal polymerization method. Main benefits from their application is increasing of the conversion rate and higher molecular weight of the product.[14][15] Polyaspartic acid can also be synthesized by polymerization of

ammonium hydroxide.[1][2][16]
High control over repeating unit isomers can be achieved by polymerization of N-carboxyanhydride (NCA) derivatives,[17] by polymerization of aspartic acid esters[18] or by application of enzyme catalyzed reaction.[19] Pure homopolymers, D- or L-PASA with α- or β-links only, can be synthesized using those methods.

The

α or β according to which carbonyl of it is part of the polymer chain. The α form has one carbon in the backbone in addition to the carbonyl itself (and a two-carbon sidechain) whereas the β form has two carbons in the backbone in addition to the carbonyl itself (and a one-carbon sidechain). This reaction gives a sodium poly(aspartate) composed of approximately 30% α-linkages and 70% β-linkages.[2]

Synthesis of sodium poly(aspartate)
Synthesis of sodium poly(aspartate)

Applications

Polyaspartic acid and its derivatives are biodegradable alternatives to traditional polyanionic materials, in particular polyacrylic acid.[20] PASA has ability to inhibit deposition of calcium carbonate, calcium sulfate, barium sulfate, and calcium phosphate and can be used as an antiscaling agent in cooling water systems, water desalination processes, and waste water treatment operations.[21] In addition and due to its ability to chelate metal ions, it provides corrosion inhibition.[11] It can also be used as biodegradable detergent and dispersant for various applications.[22]

PASA also has a variety of

targeting various forms of drug-containing carriers to the bone.[2] The main component of bone is hydroxyapatite (ca. 70%) (mineralized calcium phosphate). Apart from bone targeting, PASA has been modified for other biomedical applications such as drug delivery, surface coating, DNA delivery, mucoadhesion
, and beyond.[2]

As it can be synthesized in an environmentally friendly way and is

biodegradable, polyaspartate is a potential green alternative to several materials such as sodium polyacrylate used in disposable diapers and agriculture.[23][24][25] It can act as a super-swelling material in diapers, feminine hygiene products, and food packaging.[26] The level of water uptake which is inversely related to the mechanical properties of the hydrogel can be tuned by changing the crosslinking density.[4]

See also

References

  1. ^
    ISBN 978-3527306732
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  2. ^
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  3. doi:10.1016/S0141-3910(97)00184-5
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  4. ^
    PMID 31799235
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  5. ^
    ISBN 978-0-8412-1886-4
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  6. ^
    ISBN 978-3-527-30222-2
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  7. doi:10.1002/cber.18970300316
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  8. S2CID 40153017
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  10. doi:10.1021/ed082p1380
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  11. ^
    ISBN 978-0-8412-3133-7
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  12. S2CID 85201969
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  13. doi:10.1246/bcsj.51.1555
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  14. doi:10.1002/(SICI)1099-0518(20000101)38:1<117::AID-POLA15>3.0.CO;2-F
    .
  15. S2CID 85163135
    .
  16. ^ US patent 5468838, Boehmke, Gunter & Schmitz, Gerd, "Polysuccinimide, polyaspartic acid and their salts are prepared by reaction of maleic anhydride and ammonia, polycondensation of the resulting product in the presence of a solubilizing agent and, if appropriate, hydrolysis.", published 1995-11-21, assigned to Bayer AG 
  17. doi:10.1002/macp.1993.021940405
    .
  18. S2CID 84203387
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  19. PMID 12625712
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  20. PMID 12161646
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  21. doi:10.1021/ie200370v
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  22. S2CID 94818855
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  23. PMID 12161646
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  24. ^ "Presidential Green Chemistry Challenge Awards: 1996 Small Business Award: Donlar Corporation (now NanoChem Solutions, Inc.): Production and Use of Thermal Polyaspartic Acid". US Environmental Protection Agency.
  25. PMID 31799235
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  26. doi:10.1002/pat.1395
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