Synthesis and properties of monomer cast nylon-6-b-polyether amine copolymers with different structures

Abstract

TDI-polyether amine macro-initiators with different structures were synthesized to initiate the caprolactam monomer successfully, and monomer cast (MC) nylon-6-b-polyether amine copolymers with multi-branched molecular structure were prepared via an in situ polymerization. It was found that the apparent activation energy (E) and the pre-exponential factor (A) of the reaction increased for the copolymers, and the TDI-polyether amine macro-initiators presented low reactivity due to the steric effects of the multi-armed long-chain structure. The hydrogen bond and inter-molecular forces of the copolymers were weakened by the introduction of multi-branched molecular chains, which was in favor of the formation of a γ-crystal. The crystallization ability decreased for the copolymers, among which MC nylon-6-b-PP3A with an extra branched-chain showed the highest melting and crystallization temperatures and crystallinity with a relatively large crystal grain size. A pseudo-plastic fluid characteristic of flow behavior was observed for MC nylon-6. The viscoelastic moduli (G) and entanglement density (ν_e) of all copolymers were higher than that of neat MC nylon-6 due to severe entanglement of the large quantity of multi-branched molecular chains of the copolymers resulting in the formation of physical networks, of which MC nylon-6-b-PP3A presented the highest. In the meantime, the values of the loss factor of the copolymers increased and the storage modulus and glass transition temperature (T_g) decreased. The stress–strain curves of all copolymers showed an untypical yield point and presented obvious strain hardening behavior, while a hairy fibrous structure was observed on the fracture surface of the copolymers, indicating the notable toughening effect of polyether amine on the nylon-6 matrix. The toughening mechanism of the copolymers was deduced as a multi-layer crack extension mechanism.