Raman study of lactide oligomer structure: molecular architecture, arm length and number, enantiomeric composition, crystallinity degree
Bortsova A.N.1,2, Kozlova L.Yu.2, Liubimovskii S.O.2, PuchkovA.A.3,4, Kalinin K.T.3,4, Novikov V .S.2, Kuznetsov S.M.2; 1Mendeleev University of Chemical Technology of Russia; 2Prokhorov General Physics Institute of the Russian Academy of Sciences;3 National Research Center «Kurchatov Institute»;4 N.S. Enikolopov Institute of Synthetic Polymeric Materials of the Russian Academy of Sciences
Abstract
Lactide oligomers (OLA) have great potential in the development of biodegradable
compositions for 3D printing, targeted drug delivery systems, and
tissue-engineering constructions. In practice, modified OLA are also used as
additives to polylactide (PLA) to enhance its mechanical performance. The
performance of such materials is governed by molecular architecture, chain length,
stereochemistry, and crystallinity degree (CD). Fast, non-destructive ways to
quantify these features in OLA remain underdeveloped. Raman spectroscopy is a
promising tool, but robust correlations tailored to OLA — rather than
high-molecular-weight PLA — are still lacking.
This work addresses this gap by establishing how the Raman spectra of OLA
depend on molecular architecture (linear and star-shaped), arm length and number,
enantiomeric composition, and CD. We studied partially crystalline and amorphous
oligomers of L-lactide (L-OLA) and amorphous oligomers of D,L-lactide
(D,L-OLA). Additionally, X-ray diffraction analysis (for CD determination) and
NMR spectroscopy (for determining the degree of polymerization (DP)) were used.
The most important results of the work are:
1. It is shown that the method for determining the CD of PLA, previously
proposed for high-molecular-weight PLA and lactide copolymers, works
effectively for the case of L-OLA of linear and star-shaped architecture.
2. The CD of linear and star-shaped L-OLA increases with an increase in the
DP and with a decrease in the number of arms.
3. A method for estimating the DP of L-OLA and D,L-OLA is proposed, based
on measuring the ratio of the peak intensities of the Raman lines of PLA
and the co-initiator of the synthesis.
4. Raman bands corresponding to molecules in disordered conformations were
identified, as well as Raman lines of L-lactide that appear in the oligomer
spectra at incomplete monomer conversion.
Thus, it is shown that Raman spectroscopy is an effective method for analyzing the
structure of linear and star-shaped OLA.
Speaker
Alena
Mendeleev University of Chemical Technology of Russia
Russia
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