Novel bio-based and biodegradable block copolymers were synthesized by “click” reaction between poly(L-lactide) (PLLA) and polyamide 4 (PA4). Upon tuning the molar mass of PLLA block, the properties of copolymers and electrospun ultrafine fibers were investigated and compared with those of PLLA and PA4 blends. PLLA and PA4 were found incompatible and formed individual crystalline regions, along with reciprocal inhibition in crystallization. Electrospun fibers were highly hydrophobic, even if hydrophilic PA4 was the rich component. The crystallinity of either PLLA or PA4 decreased after electrospinning and PLLA-rich as-spun fibers were almost amorphous. Immersion tests proved that fibers of block copolymers were relatively homogeneous with micro-phase separation between PLLA and PA4. The fibrous structures of copolymers were different from those of the fibers electrospun from blends, for which sheath-core structure induced by macro-phase separation between homopolymers of PLLA and PA4 was confirmed by TEM, EDS, and XPS.
Long-chain hyperbranched polyesters (LHBPx, x = 1, 2, 3) with varying lengths of branched chains were synthesized through a thiol-ene click reaction. Subsequently, LHBPx was incorporated into PA4 via the solution method to prepare a LHBPx/PA4 polymer blend, aiming to address the limitations of PA4, such as its narrow thermal processing window (△T = Td5−Tm) and high brittleness. The results demonstrated that the addition of LHBPx enhanced the △T of PA4 from 1.6 °C to 14.5 °C (LHBP3/PA4), increasing the rheological properties of LHBPx/PA4 polymer blends, thereby improving its thermal processability. Compared with PA4, the elongation at the break of the LHBP3/PA4 polymer blend was increased by 20.4%, and the brittle fracture was changed into a ductile fracture. The crystallinity of PA4 was greatly decreased, from 54.41% to 37.42%, owing to the incorporation of LHBPx, whereas Tmof PA4 had almost no change. It was explained that LHBPx hindered the crystal growth stage, whereas it promoted the nucleation stage of PA4, resulting in no significant change in crystal type. Moreover, the longer the branched chain of LHBPx was, the more pronounced the improvement in the thermal processability and toughness of PA4 became. Above all, this work was meaningful for the potential application of PA4 in industrial plastics.
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