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Blends of nylon-6 and EPDM-rubber were prepared with various rubber contents (0-20 wt ~o) and particle sizes (0.3-1.6 #m). The effects of rubber concentration and particle size on the tensile modulus, torsion modulus, yield stress and notched impact strength of the blends were studied. Blend structures and fracture surfaces were investigated by scanning electron microscopy. Rubber particles induce a sharp brittle-tough transition which is independent of the glass transition temperature of the nylon matrix. The brittle-tough transition temperature for notched Izod impact tests shifts to lower values when the rubber content is increased or the particle size is decreased. A correlation was found between the brittle-tough temperature and the interparticle distance. Two deformation modes were observed: voiding and shear yielding. Particle size and interfacial adhesion affect neither the yield stress nor the modulus of the blends.

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Poly(tetramethylene oxide)-based poly(ether ester amide)s with monodisperse tetraamide segments were synthesized. The tetraamide segment was based on adipic acid, terephthalic acid, and hexamethylenediamine. The synthesis method of the copolymers and the influence of the tetraamide concentration, which was varied between 3 and 44 wt %, were studied. The copolymers were characterized by differential scanning calorimetry and temperature-dependent Fourier transform infrared, small-angle X-ray scattering, atomic force microscopy, and dynamic mechanical thermal analysis. The monodisperse tetraamide segments crystallized fast, forming crystalline ribbons with high aspect ratios, and the crystallinity of the tetraamide segments in the copolymers was typically 90%. The glass-transition temperature of the poly(tetramethylene oxide) phase was low (À65 to À708C), and the modulus in the plateau region of the copolymers was virtually temperature-independent. With increasing content of crystallizable amide segments in the copolymer, the storage modulus at room temperature increased from 1 to 102 MPa. This strong increase in the modulus with the tetraamide content could be approximated with a model for fiber-reinforced polymers.

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