Design and synthesis of POE/LLDPE functionalized with different amounts of reactive functional groups and its potential in toughening of PBT resin

Glycidyl methacrylate (GMA) and styrene (St) were grafted to the molecular chains of poly(ethylene-octene) (POE)/linear low-density polyethylene (LLDPE) using the bi-functional cooperative grafting method of in situ reactive melting grafting technology to prepare a series of GMA-functionalized (POE/LLDPE)-g-(GMA-co-St) graft copolymers. Then the graft copolymers were blended with poly(butylene terephthalate) (PBT) to prepare PBT/(POE/LLDPE)-g-(GMA-co-St) blends. The effects of the reactive functional group amount (GMA) in the graft copolymer on the rheological, thermal, and mechanical properties and phase morphology of the blends were studied in detail, and the toughening mechanism was analyzed comprehensively. The results showed that the (POE/LLDPE)-g-(GMA-co-St) graft copolymers had a good toughening effect on the PBT resin, and the compatibility between PBT and the dispersed phase could be effectively improved by introducing a small amount of GMA in the graft copolymers. The Izod impact strength, tensile strength and elongation at break of the PBT/(POE/LLDPE)-g-(GMA-co-St) blends were significantly improved, and blends with excellent comprehensive properties were obtained. Furthermore, the thermal stability, dynamic modulus, and complex viscosity of the blending system gradually increased, the size of the dispersed phase particles gradually decreased, and the mechanical properties gradually increased with increased GMA amount in the graft copolymer (2–5 wt%). Additionally, the blends were fractured in a ductile manner within the GMA amount range investigated. Cavitations were created inside the (POE/LLDPE)-g-(GMA-co-St) particles. Their exfoliation released three-dimensional static stress to initiate matrix yielding and absorb more energy to achieve better toughness of the blends. However, the reaction system underwent severe cross-linking side reactions when the GMA amount added in the graft copolymer was too high (6 wt%), deteriorating the performance of (POE/LLDPE)-g-(GMA-co-St) and ultimately damaging the phase morphology of the blends and their mechanical properties.