Enhancing the Crystallization Performance of Poly(L-lactide) by Intramolecular Hybridizing with Tunable Self-assembly-type Oxalamide Segments

In this work, hydroxyl-terminated oxalamide compounds N 1 , N 2 -bis(2-hydroxyethyl)oxalamide (OXA1) and N 1 , N 1′ -(ethane-1,2-diyl)bis( N 2 -(2-hydroxyethyl)oxalamide (OXA2) were synthesized to initiate the ring-opening polymerization of L-lactide for preparation of oxalamide-hybridized poly(L-lactide) (PLA OXA ), i.e. , PLA OXA1 and PLA OXA2 . The crystallization properties of PLA were improved by the self-assembly of the oxalamide segments in PLA OXA which served as the initial heterogeneous nuclei. The crystal growth kinetics was studied by Hoffman-Lauritzen theory and it revealed that the nucleation energy barrier of PLA OXA1 and PLA OXA2 was lower than that of PLA. Consequently, PLA OXA could crystallize much faster than PLA, accompanied with a decrease in spherulite size and half-life crystallization time by 74.8% and 86.5% (T = 125 °C), respectively. In addition, the final crystallinity of PLA OXA1 and PLA OXA2 was 6 and 8 times higher, respectively, in comparison with that of neat PLA under a controlled cooling rate of 10 °C/min. The results demonstrate that the hybridization of oxalamide segments in PLA backbone will serve as the self-heteronucleation for promoting the crystallization rate. The higher the content of oxalamide segments (PLA OXA2 compared with PLA OXA1 ) is, the stronger the promotion effect will be. Therefore, this study may provide a universal approach by hybridizing macromolecular structure to facilitate the crystallization of semi-crystalline polymer materials.