A Unique Meta‐Form Structure in the Stereocomplex of Poly(<scp>D</scp>‐lactic acid) with Low‐Molecular‐Weight Poly(<scp>L</scp>‐lactic acid)

Chang, Liuwen; Woo, Eamor M.

doi:10.1002/macp.201000375

Cited by 30 publications

(15 citation statements)

References 47 publications

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“…Both P hc and P sc shift to low q with increasing T c , meaning the enhancement of long period of hc and sc crystallites (Table 3). Long periods of sc crystallites range 11−17 nm, which agree with the results reported by Li et al 57 and Woo et al 58 It is notable that, at the same T c , the long period of sc crystallites is much smaller than that of homocrystallites. Long diffusion path and large kinetic barrier of stereocomplexation may restrict the formation of thick crystalline lamellae.…”

Section: ■ Experimental Sectionsupporting

confidence: 91%

Competitive Stereocomplexation, Homocrystallization, and Polymorphic Crystalline Transition in Poly(l-lactic acid)/Poly(d-lactic acid) Racemic Blends: Molecular Weight Effects

et al. 2015

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Competitive crystallization kinetics, polymorphic crystalline structure, and transition of poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) racemic blends with a wide range of molecular weights (MWs) were symmetrically investigated. Stereocomplex (sc) crystallites are exclusively formed in the low-MW racemic blends. However, stereocomplexation is remarkably depressed, and homocrystallization becomes prevailing with increasing MWs of PLLA and PDLA. Suppressed stereocomplexation in high-MW (HMW) racemic blends is proposed to be due to the low chain diffusion ability and restricted intermolecular crystal nucleation/growth. Equilibrium melting point of sc crystallites first increases and then decreases as MW increases. Crystallinity and relative fraction of sc crystallites in racemic blends enhance with crystallization temperature (Tc), and the sc crystallites are merely formed at Tc > 170 °C because of their higher thermodynamic stability. In situ wide-angle X-ray diffraction (WAXD) analysis reveals that the stereocomplexation and homocrystallization are successive rather than completely simultaneous, and the stereocomplexation is preceding homocrystallization in isothermal crystallization of HMW racemic blends. Both initial crystalline structure of homocrystallites (hc) and MW influence the heating-induced hc-to-sc transition of HMW racemic blend drastically; the hc-to-sc transition becomes easier with decreasing Tc and MW. After crystallization at the same temperature, sc crystallites show smaller long period than their hc counterparts.

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Section: ■ Experimental Sectionsupporting

confidence: 91%

Competitive Stereocomplexation, Homocrystallization, and Polymorphic Crystalline Transition in Poly(l-lactic acid)/Poly(d-lactic acid) Racemic Blends: Molecular Weight Effects

et al. 2015

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“…In addition, the preorder state melted completely and recrystallized with the unmelted original crystals, which acted as nuclei, when T a was higher than 225 °C [Figure (b)]. We observed that the preorder state was different from the δ (or α′, disordered α) form of PLA . As reported in these studies, the δ form of PLA was attained upon certain crystalline conditions and characterized by in situ WAXD and IR spectroscopy; it transformed into the α form upon direct heating, and this was considered a solid‐to‐solid transition .…”

Section: Discussionsupporting

confidence: 51%

Microstructure and melting behavior of a solution‐cast polylactide stereocomplex: Effect of annealing

Shao

Zhou

et al. 2016

J of Applied Polymer Sci

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The effect of annealing on the microstructure and melting behavior of a solution-cast polylactide (PLA) stereocomplex (sc) was systematically investigated by differential scanning calorimetry and small-angle X-ray scattering. A preorder state, an intermediate form between the amorphous and crystalline states, was found in the solution-cast poly(L-lactide)-poly(D-lactide) blend. When the annealing temperature (T a ) was below 220 8C, a part of the preorder state directly formed thicker sc crystallites; these corresponded to the second melting peak, which appeared around 250 8C during the heating process. Although the rest melted and became the amorphous phase, it formed a thinner lamella under the restriction of the unmelted initial sc crystallites during annealing; the melting process of this lamella was parallel to that of the new melting peak, which appeared around 220 8C. The melting of the initial crystal formed as the solvent volatilized corresponded to the range of the first melting temperature around 230 8C. When T a was above 220 8C, the preorder state melted completely, and the initial crystal experienced perfection process. Furthermore, the highest melting temperature of PLA sc (254.1 8C, with a fusion enthalpy of 125.5 J/g) was obtained when T a was 235 8C.

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“…The exotherm was attributed to the cold crystallization of homocrystals. It was related to α ′ crystal formation [23]. An additional exotherm was observed on the non-reversing curve between approximately 105 °C and 165 °C.…”

Section: Resultsmentioning

confidence: 99%

Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating

Shyr

Chen

2019

Polymers

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A series of poly(l-lactide)/poly(d-lactide) blended chips (LDC), as-spun LD fibers (LDA) and hot-drawn LD fibers (LDH) were prepared for investigating the homocrystallization and stereocomplex crystallization behaviors of LDA and LDH fibers during heating. Modulated differential scanning calorimetry (MDSC), hot stage polarized microscopy (HSPM), and real-time wide-angle X-ray diffraction (WAXD) were used for studying the crystallization and melting behaviors, fiber morphology, and crystalline structure evolution of the LDA and LDH fibers’ homocrystals and stereocomplex crystals during heating. The molecular chain orientations of the LDA and LDH fibers were obtained through spinning and improved through the hot drawing processes. When the molecular chain was oriented on the fiber axis, the homocrystals and stereocomplex crystals of the fibers began to form in turn as the heating temperature exceeded the glass transition temperature of the fiber. The side-by-side packing of the molecular chains was promoted by mixing the molecular chains with the extrusion screw during the spinning process, facilitating stereocomplex crystallization. When the LDA fiber was heated above the glass transition temperature of the fiber, movement of the fiber molecular chain—including molecular chain orientation and relaxation, as well as crystallization, melting, and recrystallization of homocrystals and stereocomplex crystals—were investigated through HSPM. MDSC and real-time WAXD were used to observe the molecular chains of the melted poly(l-lactide) and poly(d-lactide) homocrystals of the fibers rearranging and transiting to form stereocomplex crystals during heating.

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A Unique Meta‐Form Structure in the Stereocomplex of Poly(D‐lactic acid) with Low‐Molecular‐Weight Poly(L‐lactic acid)

Cited by 30 publications

References 47 publications

Competitive Stereocomplexation, Homocrystallization, and Polymorphic Crystalline Transition in Poly(l-lactic acid)/Poly(d-lactic acid) Racemic Blends: Molecular Weight Effects

Competitive Stereocomplexation, Homocrystallization, and Polymorphic Crystalline Transition in Poly(l-lactic acid)/Poly(d-lactic acid) Racemic Blends: Molecular Weight Effects

Microstructure and melting behavior of a solution‐cast polylactide stereocomplex: Effect of annealing

Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating

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