Determination of Polylactide Microstructure by Homonuclear Decoupled ¹H NMR Spectroscopy

Abstract

The ring‐opening polymerization (ROP) of lactide (the dilactone of lactic acid) produces poly(lactide) commonly referred to as poly(lactic acid) (PLA). The monomer lactide, has two stereogenic centers and thus, three stereoisomers are possible, namely: D‐(R,R), L‐(S,S) and meso‐lactide. The rac‐lactide is an equimolar mixture of D‐ and L‐enantiomers. Depending upon the relative configuration of the stereogenic centers in the polymeric chain, different tacticities (isotactic, syndiotactic, heterotactic and atactic) arise in the PLA chains. The study of the tacticity of a polymer is fundamental since it plays a crucial role in determining the physical properties of the polymer. NMR spectroscopy is a powerful analytical technique for the determination of the tacticity of PLA. This article describes in details the tacticity assignment for PLA derived from ROP of rac‐lactide and meso‐lactide, using homonuclear proton‐decoupled 1H NMR. The detailed tetrad level assignment pertinent to the methine hydrogen signal is the key for the determination of tacticity.

Synthesis and Characterization of Well-Defined High-Molecular-Weight PDLA-b-PLLA and PDLA-b-PLLA-b-PDLA Stereo-Block Copolymers

“…32,40 The prevailingly isotactic polylactides are obtained with the Bi catalyst via the sequential addition of L-LA and D-LA. 13 C NMR and HD 1 H NMR of these copolymers revealed precise block regio-and stereoregularities and confirmed their very high tacticity, 32,51 which supports full monomer conversion after each step and negligible racemization.…”

Mononuclear Zn(ii) compounds supported by iminophenolate proligands binding in the bidentate (N, O) and tridentate (N, O, S) coordination mode: synthesis, characterization and polymerization studies

“…The tacticity of PLA (Table 1) achieved from our catalyst library was calculated by comparing the normalized integration of the methine region of homonuclear decoupled 1 H NMR spectra with the Bernoullian statistics from which the probability of isotactic linkages ( P m ) or heterotactic linkages ( P r ) for rac -LA was determined. 81 Compounds 1–4 resulted in the formation of heterotactic-enriched PLA with P r ranging between 0.63 and 0.67. However, 5–8 resulted in isotactic-enriched PLA with P m ranging between 0.72 and 0.78 (ESI†).…”

Bimetallic Al(III) Compounds as Catalysts for the Synthesis of Biodegradable Polyesters and Polycarbonates

“…[e] Measured by GPC at 40 °C. [f] Calculated from the homonuclear decoupled 1 H NMR spectrum after deconvolution [43] …”