Deuteration Network Members Involved: ESS, FZJ
Project Description: This aim of this collaborative project is to synthesise stereo-defined, deuterium-labelled samples of poly(lactic acid) (Figure 1: stereochemistry omitted).
Figure 1. The structure of poly(lactic acid) (undefined stereochemistry).
Poly(lactic acid) is an increasingly important polymer because it can be derived from renewable resources and is recyclable and biodegradable.
Figure 2. Cups made from poly(lactic acid).
It’s physical properties relating to biodegradability can be tuned by changing the stereochemistry of the monomer from which it is synthesised, lactide. Lactide exists as three enantiomers, (R,R), (S,S) and (R,S), and poly(lactic acid) can exist in several forms, including isotactic (from all (R,R)-lactide, or all (S,S)-lactide) and hetero- and syndiotactic (from a mixture of (R,R)- and (S,S)-lactide, or from all (R,S)-lactide).
Determining the stereochemistry of poly(lactic acid) can be challenging. The technique of labelling molecules with the stable isotope deuterium should allow us to analyse samples of poly(lactic acid) using neutron scattering techniques, as neutrons interact in a more useful way with deuterium atoms than the more abundant hydrogen atoms.
This project requires the synthesis of enantiopure, deuterium-labelled D- (R) and L- (S)-lactic acid, which ESS aim to perform using an enzymatic reaction starting from labelled substrate. The polymer chemists at FZJ will synthesise the stereo-defined, deuterium-labelled monomer lactide, and complete the polymerisation reaction to produce stereo-defined, deuterium-labelled poly(lactic acid) for analysis at a European neutron source.