Thermal, Crystallization, and Toughness Behavior of Polyamide 4/Long-Chain Hyperbranched Polymer Blends

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 = T_d5-T_m) 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 T_m of 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.