Enhanced crystallization kinetics of poly(lactide) with oxalamide compounds as nucleators: effect of spacer length between the oxalamide moieties

Poly(lactide), PLA, suffers from low crystallization rate. To speed up the crystallization rate, oxalamide compounds with the formula of C6H5NHCOCONH(CH2)(n)NHCOCONHC6H5 (n = 2, 4, 6, 8, 12) are synthesized as nucleating agents (NA((n))). Their thermal properties and nucleation efficiency can be tailored by tuning the aliphatic spacer length, i.e., -(CH2)(n)-. The melting temperatures and crystallization temperatures of the NA((n)) decrease monotonically with increasing n value while the thermal decomposition temperature remains constant. The aliphatic spacer length (n) of NA((n)) influences obviously the crystallization kinetics of PLA, resulting in nucleation efficiency in the sequence of NA((2)) > NA((4)) > NA((12)) approximate to NA((8)) > NA((6)). Polarized optical microscopy results show that NA((n)) could self-assemble into needle-like superstructures which subsequently promote the crystallization of PLA macromolecules. The differences in superstructural geometry and the nucleation activity of NA((n)) are responsible for the variation in the nucleation efficiency.