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 furan-terminated 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 × 10⁴ to 2.5 and 4.5 × 10⁴ 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^oC.