Molecular Architecture of Covalent Adaptable Network Additives Governs Their Integration into Melt-Processed Polyamide 6

Abstract

Covalent adaptable networks (CANs) are predominantly developed as bulk thermoset matrices, while their use as dynamically crosslinked functional phases within melt-processed thermoplastics remains largely unexplored. Here, phosphorus-containing CANs (P-CANs) with systematically varied molecular architectures are employed as macromolecular additives in polyamide 6 (PA6) to establish relationships between network structure, dynamic response, dispersion, retention, and melt processability. Transitioning from a rigid small-molecule-derived network to flexible polyphosphonate architectures shifted the glass-transition temperature from 160 to –5 °C and markedly altered stress relaxation and deformation under processing conditions. These architecture-dependent differences translated directly into thermoplastic integration: the rigid P-CAN formed larger phosphorus-rich domains and exhibited greater phosphorus retention, whereas the most flexible network appeared more uniformly dispersed, lowered processing resistance, and promoted shear-thinning behavior. The resulting balance between dispersion and retention enabled kilogram-scale twin-screw compounding and continuous film extrusion of homogeneous PA6 composites containing 5–10 wt % flexible P-CAN. Despite low final phosphorus contents (∼0.25–0.60 wt %), incorporation of the P-CANs increased limiting oxygen index, promoted char formation, and reduced microscale heat release. These results demonstrate that CAN molecular architecture provides a tunable design parameter for controlling the integration and functional performance of dynamically crosslinked polymeric additives in melt-processed thermoplastics.