Organocatalytic ring-opening polymerization of l-lactide in bulk: a long standing challenge

The exponential increase in the use of plastic demands that biosourced and biodegradable polymers such as poly(l-lactide)s (PLLA)s be considered to replace some petroleum based polymers in a range of applications. In order to produce PLLA in the greenest manner, i.e. by ring-opening polymerization (ROP) of l-lactide using an organocatalyst in solvent free conditions at high temperature (in bulk) has proven to be a significant challenge. Indeed, the high required temperature (180 °C) has led to poorly controlled polymerizations as a result of transesterification reactions of the PLLA backbone, racemization of the lactide monomers as well as the degradation and thus deactivation of the organocatalyst. We report herein the efforts made over the past 20 years in order to conduct the ROP of l-lactide in bulk by using organic molecules and the problems encountered by the scientific community in addressing this challenge to date.