Effect of arrangement of i-lactide and D-lactide in poly[(L-lactide)-co-(D- lactide)] on its resistance to hydrolysis studied by molecular modeling

Molecular modeling is used to explain how the resistance of poly[(L-lactide)-co-(D-lactide)] to hydrolysis is affected by the percentages of L- and D-lactide and their arrangements in blocks or random arrangements in the polymer. Previous studies on improving the hydrolysis resistance of PLA have involved forming either poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) polyblends or copolymers of L- and D-lactide. In this study, molecular modeling was used to study the hydrolysis resistance of PLA containing various arrangements of L- and D-lactide in the polymers. PLA copolymers are found to have less resistance to hydrolysis than a PLLA/PDLA polyblend having the same percentages of L- and D-lactide because a polyblend can form more stereocomplexes, which is the most stable structure PLA can form.