Synthesis, properties, and biodegradability of three‐branched copolyamide (4/6).

Previous studies on polyamide 4, excellent properties, functionalities, and biodegradation in natural condition have been shown. In this study, three‐branched (star‐shaped) copolyamides constituted of polyamide 4 and polyamide 6 constitutional unit were synthesized by anionic ring‐opening copolymerization of 2‐pyrrolidone with ε‐caprolactam. The thermal and mechanical properties and the biodegradability of the obtained copolyamides have been systematically investigated. The weight‐average molecular weight of the copolyamides was as high as tens of thousands (Mw 10–80 × 103 g/mol). The composition of the copolyamides was approximately in accord with the monomer feed ratio, thereby being controllable. The thermal and mechanical properties changed readily as the composition was varied (Tm 146–266°C, ΔHm 10–70 J/g, Td 278–369°C, tensile strength 28–64 MPa, elongation at break 80–750%). The copolyamide having 2‐pyrrolidone unit of 96–51 mol% exhibited biodegradability by an activated sludge. The biodegradation of the copolyamide proceeded uniformly without disproportion in constitutional unit. [ABSTRACT FROM AUTHOR]