Effect of catalyst and polymerization conditions on the preparation of low molecular weight lactic acid polymers

Kari Hiltunen, Jukka V. Seppälä*, Mika Härkönen

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    97 Citations (Scopus)

    Abstract

    The synthesis of low molecular weight (M̄n(NMR) <27 000 g/mol) lactic acid polymers by condensation polymerization of L-lactic acid was investigated. All polymerizations were carried out in the melt, using different catalysts and polymerization temperatures. The products were characterized by DSC, GPC, titrimetric methods, and 13C-NMR. According to NMR, the resulting polymers contained less than 1 mol % of lactic acid monomer and less than 6.6 mol % of lactide. In 13C-NMR studies, the molecular weights were calculated by using the previously identified end group peaks in the methine area. The calculated molecular weights were systematically smaller than the weight-average molecular weights determined by GPC and on the same order as the molecular weights determined by titrimetric methods. The weight-average molecular weights of prepared prepolymers determined by GPC varied from 3600 to 32 600 g/mol, depending on the catalyst and polycondensation conditions. In DSC studies the glass transition temperatures of the resulting polymers varied from 24 to 51 °C, and crystallinity varied from 0% to 52%. The annealing of the polymer samples had only a small effect on glass transition temperatures and crystallinity. According to our results, the best polycondensation catalyst was sulfuric acid, which produced the highest molecular weights and over 50% crystallinity. Sn(II) octoate produced quite a high molecular weight polymer which was totally amorphous (the proportion of D-lactic acid structures was about 48 mol %).

    Original languageEnglish
    Pages (from-to)373-379
    Number of pages7
    JournalMacromolecules
    Volume30
    Issue number3
    DOIs
    Publication statusPublished - 10 Feb 1997
    MoE publication typeA1 Journal article-refereed

    Keywords

    • 13C-NMR
    • lactic acid polymers
    • molecular weight determination
    • polycondensation
    • polycondensation catalysts
    • Sn(II)octoate

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