Reactive Electrospinning of Stereoblock Polylactides Prepared via Spontaneous Diels-Alder Coupling of Bis Maleimide-terminated Poly-L-lactide and Bis Furan-terminated Poly-D-lactide

Abstract

Bis maleimide-terminated poly-L-lactide (M-PLLA-M) and bis furan-terminated poly-D-lactide (F-PDLA-F) were synthesized by isocyanate coupling reactions of mono maleimide-terminated PLLA (M-PLLA) and mono furanterminated PDLA (F-PDLA) that had been prepared by the ordinary ring opening polymerization of L-and D-lactides with N-(2-hydroxyethyl)-maleimide and furfurylamine as the initiators, respectively. Both the M-PLLA-M and F-PDLA-F were dissolved in CH2Cl2 in 1 : 1 ratio and subjected to the ordinary electrospinning where the initial polymer concentration was increased up to 20 wt% because of the prepolymer state of the solute and the fiber diameter could be retained in nanometer to submicron size. The molecular weight of the polymers was found to have increased from 1.0 × 10 4 to 2.5 and 4.5 × 10 4 after the electrospinning and post annealing, respectively, due to the spontaneous chain extension taking place by the terminal Diels-Alder reaction of M-PLLA-M and F-PDLA-F to form a stereoblock polylactide. The as-spun fibers were amorphous or partially semi-crystalline, whereas the annealed fibers become fully crystalline due to the formation of the stereocomplex showing a melting temperature above 200°C.

Macromolecular design of specialty polylactides by means of controlled copolymerization and stereocomplexation

“…Yamane and colleagues reported a melt‐blending of PLLA and PDLA at a temperature between the T m of hc and sc crystals where sc crystallization can be selectively promoted with hc crystal fusing . Our groups focused on the molecular level mixing state of the PLLA and PDLA segments in sb‐PLAs consisting of PLLA and PDLA block sequences . Yui et al first synthesized stereo diblock PLAs (di‐sb‐PLA) to find the preferential sc formation .…”

“…Three methods are available for the synthesis of sb‐PLA having different PLLA and PDLA sequences: (1) two‐step ROP of d ‐ and l ‐lactides, (2) melt/solid combination polycondensation with l ‐ and d ‐lactic acids as the starting monomers and (3) polymer coupling of terminal‐functionalized PLLA and PDLA (Table ). Two‐step ROP is suitable for obtaining di‐sb‐PLAs as well as stereo triblock PLAs (tri‐sb‐PLA), particularly for synthesizing those having controlled PLLA/PDLA compositions.…”

Melt-Blown Cross-Linked Fibers from Thermally Reversible Diels–Alder Polymer Networks

“…In this study, we introduce a one-step approach for producing cross-linked fibers by melt blowing a thermoreversible polymer network ,− with dynamic cross-links. Unlike conventional thermosets, reversible networks can undergo dynamic molecular rearrangement to achieve macroscopic flow in response to external stimuli (e.g., heat), exhibiting self-healing capability and reprocessability/recyclability. ,− Here, a thermoreversible network comprised of methacrylate-based backbones with functional pendants that can participate in covalent cross-linking by forming Diels–Alder linkages was selected. A Diels–Alder reaction ,− is defined as a [4 + 2] cycloaddition between a conjugated diene (e.g., furan) and a dienophile (e.g., maleimide) (Figure A).…”

“…Unlike conventional thermosets, reversible networks can undergo dynamic molecular rearrangement to achieve macroscopic flow in response to external stimuli (e.g., heat), exhibiting self-healing capability and reprocessability/recyclability. ,− Here, a thermoreversible network comprised of methacrylate-based backbones with functional pendants that can participate in covalent cross-linking by forming Diels–Alder linkages was selected. A Diels–Alder reaction ,− is defined as a [4 + 2] cycloaddition between a conjugated diene (e.g., furan) and a dienophile (e.g., maleimide) (Figure A). Below a certain temperature (usually ∼100 °C), furan–maleimide linkages remain connected, and the Diels–Alder network behaves like a thermoset.…”

“…Below a certain temperature (usually ∼100 °C), furan–maleimide linkages remain connected, and the Diels–Alder network behaves like a thermoset. At elevated temperatures (>100 °C), furan–maleimide linkages cleave and revert to free furan and maleimide functionalities through a retro-Diels–Alder reaction, forming de-cross-linked materials with thermoplastic characteristics. ,− Upon heating to a certain temperature, they possess an appropriate viscosity for melt blowing, while upon cooling during/after melt blowing, the Diels–Alder reaction again produces cross-linked fibers. Reversibly cross-linked fibers can be recycled because of their dynamic nature, potentially promoting sustainability for nonwoven fiber products.…”