Promoted stereocomplex formation and two‐step crystallization kinetics of poly(
            <scp>l</scp>
            ‐lactic acid)/poly(
            <scp>d</scp>
            ‐lactic acid) blends induced by nucleator

Xie, Qing; Han, Lina; Shan, Guorong; Bao, Yongzhong; Pan, Pengju

doi:10.1002/pcr2.10057

Cited by 6 publications

(3 citation statements)

References 59 publications

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“…On the basis of elaborate exploration, many strategies have been reported to promote the formation of SC. These include the synthesis of stereo-block PLLA- b -PDLA, − melt blending at a temperature between the melting points of SC and HC, , adding nucleating agents, , flow-induced crystallization, ,, high temperature annealing, , etc. In spite of all this effort, crystallization of pure SC still remains an unsolved challenge, especially in a high-molecular-weight (HMW) PLLA/PDLA racemate. − …”

Section: Introductionmentioning

confidence: 99%

Poisoning by Purity: What Stops Stereocomplex Crystallization in Polylactide Racemate?

et al. 2023

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Formation of stereocomplex crystals (SC) is an effective way to improve the heat resistance and mechanical performance of poly(lactic acid) products. However, at all but the slowest cooling rates, SC crystallization of a high-molecular-weight poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) racemate stops at a high temperature or does not even start, leaving the remaining melt to crystallize into homochiral crystals (HC) or an SC–HC mixture on continuous cooling. To understand this intriguing phenomenon, we revisit the SC crystallization of both high- and low-molecular-weight PLLA/PDLA racemates. Based on differential scanning calorimetry (DSC), supplemented by optical microscopy and X-ray scattering, we concluded that what stops the growth of SC is the accumulation of the nearly pure enantiomer, either PDLA or PLLA, that is rejected from the SC ahead of its growth front. The excess enantiomer is a result of random compositional fluctuation present in the melt even if the average composition is 1:1. The situation is more favorable if the initial polymer is not fully molten or is brought up to just above the melting point where SC seeds remain, as proven by DSC and X-ray scattering. Moreover, we find that not only is SC growth poisoned by the locally pure enantiomer but also that at lower temperatures, the HC growth can be poisoned by the blend. This explains why SC growth, arrested at high temperatures, can resume at lower temperatures, along with the growth of HC. Furthermore, while some previous works attributed the incomplete SC crystallization to a problem of primary nucleation, we find that adding a specific SC-promoting nucleating agent does not help alleviate the problem of cessation of SC crystallization. This reinforces the conclusion that the main problem is in growth rather than in nucleation.

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Section: Introductionmentioning

confidence: 99%

Poisoning by Purity: What Stops Stereocomplex Crystallization in Polylactide Racemate?

et al. 2023

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“…However, this method is limited because not all polymers experience as drastic of a difference in T m between its homocrystallite and stereocomplex forms. A way to address this is the addition of organic or inorganic compounds called nucleators that selectively induce stereocomplex crystallization. − By specifically enhancing the noncovalent forces that drive stereocomplexation, these nucleating agents can also significantly enhance the crystallization rate of the complex. − Future research needs to be done to see whether these or other methods used to enhance the crystallinity and crystallization rate of SC-PLA can be applied to other SC-polyesters or even other SC-scaffolds.…”

Section: Future Directionsmentioning

confidence: 99%

Underexplored Stereocomplex Polymeric Scaffolds with Improved Thermal and Mechanical Properties

Tutoni

Becker

2020

Macromolecules

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Stereocomplexation has been shown to enhance the thermal and mechanical properties of polymers. The scope and utility of stereocomplexation have focused primarily on toughening of poly(l-lactic acid) (PLLA). Recently, additional polyester and polycarbonate systems with more diverse properties and functionality have also exhibited the ability to form stereocomplexes which is coupled to enhanced thermal properties similar to those exhibited by stereocomplexed-PLA (SC-PLA). This Perspective will highlight recent and future efforts that aim to discover new stereocomplexable scaffolds and expand their use in the formation of molecular and supramolecular assemblies and in biomaterial applications.

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“…In comparison with liner PLLA/PDLA blends, star-shaped and comblike ones have been proven to exhibit markedly enhanced SC crystallizability, probably owing to the favored interactions between enantiomeric PLA branches and the increased segment mobility [34,[37][38][39][40][41]. Nevertheless, such unique PLAs have not been industrially produced up to now, so considerable efforts have recently been devoted to gain exclusive SC crystallization of commercial linear high-MW PLLA/PDLA blends by incorporating certain processing additives (e.g., plasticizers [42][43][44], compatibilizers [22,45,46], and nucleating agents [47][48][49][50]). For example, Yang et al [51] first reported that poly (ethylene glycol) (PEG) can facilitate the SC crystallization of PLLA/PDLA blends by increasing segment mobility and diffusion ability as a plasticizer.…”

Section: Introductionmentioning

confidence: 99%

Substantially Enhanced Stereocomplex Crystallization of Poly(L-lactide)/Poly(D-lactide) Blends by the Formation of Multi-Arm Stereo-Block Copolymers

et al. 2022

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Stereocomplex-type polylactide (SC-PLA) created by alternate packing of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) chains in a crystalline state has emerged as a growingly popular engineering bioplastic that possesses excellent hydrolytic stability and thermomechanical properties. However, it is extremely difficult to acquire high-performance SC-PLA products via melt-processing of high-molecular-weight PLLA/PDLA blends because both SC crystallites and homocrystallites (HCs) are competitively formed in the melt-crystallization. Herein, a facile yet powerful way was employed to boost SC formation by introducing trace amounts of some epoxy-functionalized small-molecule modifiers into the enantiomeric blends during reactive melt-blending. The results show that the SC formation is considerably enhanced with the in situ generation of multi-arm stereo-block PLA copolymers, based on the reaction between epoxy groups of the modifiers and hydroxyl end groups of PLAs. More impressively, it is intriguing to find that the introduction of only 0.5 wt% modifiers can induce exclusive SC formation in the blends upon isothermal and non-isothermal melt-crystallizations. The outstanding SC crystallizability might be attributed to the suppressing effect of such unique copolymers on the separation of the alternately arranged PLLA/PDLA chain segments in molten state as a compatibilizer. Furthermore, the generation of these copolymers does not result in a significant increase in melt viscosity of the blends. These findings suggest new opportunities for the high-throughput processing of SC-PLA materials into useful products.

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Promoted stereocomplex formation and two‐step crystallization kinetics of poly( l ‐lactic acid)/poly( d ‐lactic acid) blends induced by nucleator

Cited by 6 publications

References 59 publications

Poisoning by Purity: What Stops Stereocomplex Crystallization in Polylactide Racemate?

Poisoning by Purity: What Stops Stereocomplex Crystallization in Polylactide Racemate?

Underexplored Stereocomplex Polymeric Scaffolds with Improved Thermal and Mechanical Properties

Substantially Enhanced Stereocomplex Crystallization of Poly(L-lactide)/Poly(D-lactide) Blends by the Formation of Multi-Arm Stereo-Block Copolymers

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