Chiral nature of Poly-lactide demystified

PolySciTech division of Akina, Inc (www.polyscitech.com) provides a wide array of polymers including poly(lactide). A common question I receive is about chirality as it applies to poly-lactide (PLA). If you’re like most scientists, your memories of chirality likely include staring at your right and left hands during your Organic-Chem 200 level exam trying desperately to remember which one was D and which one was L so you could put the right answer down for the test. Luckily, here, it’s simple. For poly(lactide) the important aspect of chirality applies in regards to the side-methyl unit orientation relative to the main chain. This affects the ‘tacitity’ of the polymer and in this case, pure chiral form (D or L, respectively) has the methyl units arranged on one side of the polymer chain which allows for close-stacking and crystallinity of the polymer. Conversely, the racemic mixture (D,L) has the methyl units randomly arranged which reduces crystalline formation. This minor detail strongly affects the resultant properties of the polymer as pure-chiral PLA tends to have higher mechanical stiffness but slower degradation while DL racemic PLA has more flexibility with faster degradation. PolySciTech sells both types so you can find the right one for your application.