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ABSTRACT:The toughening enhancement of Polyamide 6 blended with different types of functionalized elastomers was studied. Morphological analysis by scanning electron microscopy (SEM) were performed on undeformed samples in order to determine particle-size distribution. Yet more SEM examination of the damage zone ahead of notch tip in uniaxial tensile test provided insight into the failure mechanisms. The best impact strength was achieved with the PA6/EPDM-g-MA (terpolymer ethylene-propylene-diene monomer grafted with Maleic Anhydride) blend, unlike ULDPE-g-MA (ultra-low-density polyethylene grafted with maleic anhydride), which possesses the poorest toughening efficiency even though opposite results would be expected from particle-size evaluation. The higher cavitation resistance of EPDM compared to UL-DPE observed during low strain rate tensile test plays a crucial role in understanding the best performances of its blends.

SYNOPSISThe relationship of blend morphology to deformation mechanisms and notched Izod impact strength was studied with three butadiene-based impact modifiers for polycarbonate ( P C ) .The impact modifiers were a linear polybutadiene ( P B ) , a styrene-butadiene-styrene block copolymer (SBS) , and a structured latex particle having a P B core and methyl methacrylate/ styrene shell (MBS). The particle-size distribution in the blends was determined from transmission electron micrographs ( T E M ) . Fractographic analysis combined with TEM examination of thin sections from impacted specimens provided insight into the failure mechanisms. Good impact was achieved with PC/MBS blends when cavitation of the coreshell particles relieved triaxiality and enabled the matrix to fracture by the plane stress ductile tearing mode that is characteristic of thin PC. The best impact properties were obtained with PC /SBS blends when the modifier was dispersed as aggregates of small particles. Cavitation at the weak internal boundaries relieved triaxiality, but subsequent coalescence of cavitated particles during ductile drawing of the matrix created critical size voids and the resulting secondary cracks reduced the toughness of the blend. In general, P B did not significantly enhance the impact strength of PC. 0 1994 John Wiley & Sons, Inc. INTRODUCTIONPolycarbonate ( PC ) is an engineering thermoplastic with excellent clarity, high heat-deflection temperature, and toughness in thin sections. However, its notched impact properties become poorer as the thickness increases. This notch sensitivity is due to the change in stress state at the notch from plane stress to plane strain and the resulting change in failure mechanism from shearing to crazing. The notch sensitivity can be reduced by blending a small amount of an elastomer with PC. Cavitation of the elastomer relieves the triaxiality at the notch and permits the matrix to deform by ductile shearing. The effectiveness of the elastomer in this function depends on various factors; the ones of particular interest in this study are the chemical architecture of the elastomer and the dispersion of the elastomer in the matrix.' * To whom correspondence should be addressed. Linear polybutadiene ( P B ) alone is not commonly used for toughening ductile matrices. Without cross-linking, it has poor strength, and being difficult to disperse, the morphology of its blends is difficult to control. Instead, PB is incorporated as a component into copolymers or terpolymers of various architectures such as styrene-butadiene-styrene block copolymer (SBS) and structured latex particles with methyl methacrylate/styrene (MBS 1.Styrenic block copolymers with high elastomer content possess a phase-separated morphology in which polystyrene (PS) domains function as physical cross-links for the continuous PB phase. These copolymers are quite attractive as impact modifiers because they significantly improve the toughness at relatively low Nevertheless, elastomer dispersion depends on the processing condit...

13C NMR analysis of propene/l -butene block copolymers obtained by gas-phase polymerization with Ziegler-Natta catalysts allows the determination of the propagation rate constants for the homopolymerization of the two monomers. They are very similar for the Solvay type catalyst 6-TiCI3/AIMe3 and the supported catalyst TiC1,/MgCl,/phthalate/AlMe3. The constant of propene polymerization is three times higher than that of 1-butene polymerization. The high value of the constant found for propene polymerization is in agreement with the literature value determined by the stopped flow polymerization method.