Synergistic effect of star‐shaped architecture and poly(ethylene glycol) moieties on poly(lactic acid) stereocomplex crystallization behaviors

Abstract

Stereocomplex (sc) crystal formation represents an important strategy to improve the physical properties of poly(lactic acid) (PLA), including enhanced thermal resistance, anti‐hydrolysis and mechanical performance. Therefore, understanding and controlling the sc crystallization behaviors is an important and widely studied research topic. Herein, we investigate the cooperative effect of star‐shaped PLA chain topology and poly(ethylene glycol) incorporation on sc formation. We synthesize a series of poly(lactides), including poly(l‐lactic acid) (PLLA), poly(d‐lactic acid), star‐shaped PLLA and poly(d‐lactic acid)‐poly(ethylene glycol)‐poly(d‐lactic acid) (DED) triblock copolymer, via ring‐opening polymerization of lactide, followed by solution blending to form PLA stereocomplexes (scPLAs). The chemical structure of the prepared scPLAs is characterized by Fourier transform infrared and nuclear magnetic resonance, whereas the crystallization behavior and spherulite morphology are investigated by wide‐angle X‐ray diffraction, DSC and polarized optical microscopy. Linear PLLA/star‐shaped poly(d‐lactic acid) presents rapid crystallization behaviors and high crystallinity due to the excellent nucleation ability of star‐shaped chain topology. For isothermal crystallization, star‐shaped PLLA/DED exhibits the fastest crystallization kinetics, the highest crystallinity and the lowest crystallization half‐time of all samples. It is found that addition of poly(ethylene glycol) segments can increase chain mobility and backbone flexibility, further facilitating the crystallization of scPLA containing star‐shaped chain architecture. These results demonstrate an effective approach to cooperatively promote scPLA formation, with potential use for practical applications. © 2022 Society of Industrial Chemistry.

Effect of oligolactic acid stereocomplex microplates as rapid crystallization nucleating agents on the properties of poly(L‐lactic acid)

“…In addition, the driving force of the stereocomplex between OLLA and ODLA may be correlated with the hydrogen bond formation between CH 3 and CO. By comparing the CO and CH 3 stretching vibration peaks of OLLA, ODLA, and SC‐OLA‐MPs, it was found that the characteristic peak of CO was shifted from 1748 to 1744 cm −1 and the location of the CH 3 stretching vibration peak also showed the same trend from 2997 to 2991 cm −1 , which was because of the formation of a large number of hydrogen bonds between the molecular chains of OLLA and ODLA, and the density of electron clouds around the functional groups decreased, thus reducing their stretching vibration frequencies and increasing the growth of chemical bonds, resulting in the migration of the stretching vibration peaks of SC‐OLA‐MPs to lower wave numbers 27 …”

“…As shown in Figure 8, the crystallinity versus time showed an “S” curve 27 . The crystallization process of the sample can be divided into three stages: the induced crystallization period, the middle crystallization period, and the late crystallization period.…”

“…As shown in Figure 8, the crystallinity versus time showed an "S" curve. 27 The crystallization process of the sample can be divided into three stages: the induced crystallization period, the middle crystallization period, and the late crystallization period. Because there were few crystal nuclei at the beginning of crystallization, the crystallization rate was slow, which increased with time and decreased in the last stage due to the nucleus extrusion collision.…”

Immobilization of Protease K with ZIF-8 for Enhanced Stability in Polylactic Acid Melt Processing and Catalytic Degradation

“…As shown in Figure 4f, the diffraction peaks of PLA at 14.8°, 16.6°, 19.0°, and 22.3°w ere assigned to (010), (110)/(200), (203), and (015) crystal planes of α-form homocrystallites, respectively. 54 Notably, after degradation, there was a significant decrease in the intensity of these characteristic peaks, indicating that these crystalline planes of PLA were disrupted by enzymatic digestion.…”