Biodegradable polyesters

1 mark · Easy

Draw the structure of the repeat unit of polylactic acid (PLA) formed from lactic acid monomers.

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Repeat unit structure of PLA: —[O—CH(CH3)—CO]—

Must show: correct backbone, ester linkage, side group (—CH3) on correct carbon

Also accept: Bracketed repeat unit with correct ester linkage and side group

Common mistakes: Incorrect positioning of CH3 group; Omission of ester linkage

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Marking points

A1 · 1 mark · Correct structure with backbone, ester linkage, and side group as shown in PLA repeat unit.

Worked solution

The repeat unit of PLA formed from lactic acid is: