Synthesis, characterization, and crystallization behaviors of poly(D-lactic acid)-based triblock copolymer

Abstract

poly(D-lactic acid) (PDLA) with different polyethylene glycol (PEG) segment synthesized PDLA-PEG-PDLA triblock copolymer through the ring-opening reaction of D-LA and PEG will be used as a toughening modifier. The microstructure, crystal structures and crystallization behaviors of this triblock copolymer were investigated by fourier transform infrared (ftiR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The triblock copolymer is synthesized from the appearance of cH 2 stretching vibration peak at 2910 cm −1 and CO stretching vibration peak at 1200 cm −1 from PEG in FTIR spectra. Moreover, the chemical shift that is about 3.6 ppm in 1 H NMR and 68.8ppm in 13 c nMR proves this matter. The results of XRD and DSC reveal that PDLA and PEG are crystallized separately, and are not fully compatible, and microphase separation has occurred in this triblock copolymer. PEG can induce the triblock copolymer to accelerate the rate of crystallization, allowing it to crystallize more completely in the same amount of time. When the molecular weight of PEG is 6000 or the ratio of D-LA/ PEG is 1/1, the crystallizability of PDLA-PEG-PDLA triblock copolymer is the best. The rapid development of industry has brought great convenience to people's lives, but the environmental pollution caused by the rapid development is also gradually exposed, coupled with the oil crisis caused by the extensive development and utilization of petroleum resources, the necessity and urgency of the research and development of degradable polymers are gradually highlighted. Among the various degradable polymers, polylactic acid (PLA) is the most promising as a green polymer material 1-3. The biggest and most prominent advantage of PLA is that it can be recycled in nature 4. Its raw materials are renewable biological resources, so it is no longer dependent on petroleum and other resources. Its wastes are completely transformed into carbon dioxide and water through hydrolysis and a series of biological metabolism, which is harmless to human body and non-toxic, and has no pollution to the environment 5,6. According to the chiral property of the structural unit, PLA can be divided into poly (L-lactic acid) (PLLA), poly (D-lactic acid) (PDLA) and poly (D , L-lactic acid) (PDLLA) 7. However, compared with polyesters with higher rigidity, PLA is a semi-crystalline polymer, which usually has a slower crystallization rate without external force and produces some amorphous products during processing 8,9. And its heat resistance is poor, which limits its application requirements in bioengineering, food packaging and other industries 10-12. Currently, in order to improve its physical or thermodynamic properties, PLA is modified by adding other substances to form composites (such as rice husk hydrochar 13 , lignin 14 , polycarbonate 15 , chitosan 16 , etc.) and polymerizing with other substances (such as PLA-PCVL-PLA 17 , SEBS-g-PLA 18 , etc.). Of course...

Effect of molecular weight of polyethylene glycol on crystallization behaviors, thermal properties and tensile performance of polylactic acid stereocomplexes

“…The triblock copolymer of PDLA-PEG-PDLA with different molecular weights of PEG (2000, 4000, 6000, and 8000) was synthesized by ring-opening polymerization of D-lactide by using PEG as an initiator and stannous octoate as a catalyst according to our previous study. 25…”

“…Our group has studied the introduction of PEG in PDLA and synthesis of triblock copolymer of PDLA-PEG-PDLA by ringopening polymerization. 25 Polarized optical microscopy (POM) showed that PEG shortened the crystallization time of the copolymer and accelerated the crystallization rate. In this work, PDLA-PEG-PDLA triblock copolymers with different molecular weight of PEG were blended with PLLA in solution to fabricate PLA stereocomplex.…”

Pyrrole Plasma Polymer-Coated Electrospun Scaffolds for Neural Tissue Engineering

“…XRD patterns of uncoated scaffolds display an amorphous structure in both randomly and aligned-oriented fibers (Figure 5). Coated scaffolds depict two diffraction peaks (a sharp one at 16.7° and at 19° one with less intensity), shown by the pPPy/I-coated scaffolds and aligned pPPy-coated scaffold, which correspond to (200)/(110) and ( 203) planes of PLA in its α-form [63][64][65]. As the process of plasma polymerization produces a XRD patterns of uncoated scaffolds display an amorphous structure in both randomly and aligned-oriented fibers (Figure 5).…”

Single-Use Plastics in the Food Services Industry: Can It Be Sustainable?

“…As PLA is a copolymer of its two enantiomeric forms, namely poly L-lactic acid and poly D-lactic acid, stereocomplexation can be applied to adjust the relative proportion of these two enantiomers, which in turn alters its properties (Rahaman et al 2020). Its properties can also be further modified through composition or polymerization with other substances (Wu et al 2020).…”