Preparation of core-shell structured polyacrylic modifiers and effects of the core-shell weight ratio on toughening of poly(butylene terephthalate)

Core-shell structured polyacrylic (named CSSP) impact modifiers consisting of a rubbery poly(n-butyl acrylate) core and a rigid poly(methyl methacrylate) shell with a size of about 353 nm were prepared by seed emulsion polymerization. The CSSP modifiers with different core-shell weight ratios (90/10, 85/15, 80/20, 75/25, 70/30, 65/35 and 60/40) were used to modify the toughness of poly(butylene terephthalate) (PBT) by melt blending. It was found that the polymerization had a very high instantaneous conversion (> 95.7%) and overall conversion (99.7%). The morphology of the core-shell structure was confirmed by means of transmission electron microscopy. Scanning electron microscopy was used to observe the morphology of the fractured surfaces. Differential scanning calorimeter was used to study the crystallization behaviors of PBT/CSSP blends. The dynamic mechanical analyses of PBT/CSSP blends showed two merged transition peaks of PBT matrix, with the presence of CSSP core-shell structured modifier, that were responsible for the improvement of PBT toughness. The results indicated that the notch impact strength of PBT/CSSP blends with a core-shell weight ratio of 75/25 was almost 8.64 times greater than that of pure PBT, and the mechanical properties agreed well with the SEM observation.