Preparation of long-chain branched poly(ethylene terephthalate): Molecular entanglement structure and toughening mechanism

Poly(ethylene terephthalate) (PET) was long-chain branched (LCB) by ring-opening reaction with both pyromellitic dianhydride and tetrahydrophthalic acid diglycidyl ester as chain extenders through reactive melt processing. It was found that with the increase of chain extenders dosage, the intrinsic viscosity of PET increased and melt index decreased greatly, while both the tensile strength and impact strength of PET were remarkably improved. The elastic modulus (G ') and viscous modulus (G '') were enhanced by chain branching. Compared with PET, the complex viscosities of LCB-PET were much higher at full frequency range, and obvious shear thinning was presented. The Cole-Cole curve deviated from the semicircular shape and the curve end was inclined to upward in high viscosity region, indicating the formation of the multiple hierarchical structures. The molecular weight of the branch (M-B) was much greater than critical entanglement molecular weight (M-e), which essentially confirmed the existence of LCB structure and fairly strong molecular entanglement in the LCB-PET molecular chain. When subjected to external force, the entanglement point, acting as physical crosslinking point between the molecules, was in favor of increasing the molecular interaction, reducing the molecular slippage, and bearing a large deformation. POLYM. ENG. SCI., 2019. (c) 2019 Society of Plastics Engineers