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Stereocomplex-Driven Hierarchical Assembly in Melt-Quenched PLLA/PDLA-Based Block Copolymer Blends
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DOI：10.1021/acs.macromol.6c01032.png)
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Abstract
En 中文
Understanding the structural evolution and stereocomplex (SC) formation in polylactide (PLA)-based block copolymer systems is of considerable interest for tailoring material properties and broadening their application potential. Herein, we investigate the crystallization and morphological evolution of poly(isoprene-b-l-lactide) (PI-b-PLLA) and poly(styrene-b-d-lactide) (PS-b-PDLA), and their equimolar blend, which promotes the formation of a noncovalent triblock terpolymer, polystyrene-SCPLA-polyisoprene (PS-SC-PI). All systems exhibit well-defined microphase-separated morphologies that are retained upon melt-quenching. Upon heating of melt-quenched block copolymers, PLLA in PI-b-PLLA crystallizes into metastable α′, β, and γ forms that transform into the α form under soft confinement. In contrast, PDLA in PS-b-PDLA crystallizes directly into the α form. Melt-quenched blends display well-ordered microphase-separated structures, while remaining largely amorphous. Upon heating, PLA crystallization occurs just above the glass transition temperature, leading to the formation of the SC and the associated mesophase, accompanied by a modest increase in microdomain spacing. At intermediate temperatures (100–160 °C), confined crystallization of both homopolymers and the SC takes place, yielding α(α′), β, γ, and SC forms within the microphase-separated framework. At higher temperatures, the β and γ forms convert into the α form, which melts near 170 °C, followed by rapid growth of the SC phase, leading to breakout crystallization and consequent disruption of the microphase-separated morphology. Above 190 °C, a new reflection at 2θ = 21.7° appears, indicating altered SC lattice packing. Similar behavior is observed for blends with different molecular weights. These results indicate that confined crystallization of PLA within noncovalent triblock terpolymers facilitates the formation of unconventional metastable crystalline phases. Overall, this work provides new insight into the mechanisms of SC formation and the hierarchical structural organization in PLA-based noncovalent triblock terpolymer systems.
Keywords:
Copolymers
Crystal structure
Crystallization
Organic polymers
Thermodynamic properties
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5.2
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3.6W
Citations:
9.4W
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