Effect of block molecular weight on the mechanical and dynamic mechanical properties of segmented polyamide

Segmented polyamides also known as polyether-ester-amides, are composed of polyether and polyamide structural units. Dynamic mechanical measurements of these polymers have been carried out over a wide range of temperatures. The polymers with hard block molecular weight of 7400 and 4100 exhibit three peaks, designated as alpha, beta and gamma in the tan delta-temperature curve. At a constant soft segment molecular weight of 1000, the alpha transition shifts to lower temperature and merges with beta transition, with decreasing hard block molecular weight. The damping also increases. However, at a constant hard block molecular weight of 1100, though the alpha and beta transitions merge together, the damping decreases on increasing the soft segment molecular weight. The mechanical properties and percent crystallinity decrease with decrease in hard block molecular weight or increase in soft segment molecular weight. The polymers with hard block molecular weight of 7400 and 4100 exhibit a higher set values and yielding characteristics. The results on dynamic mechanical studies are explained with the help of the segmented structure of the block copolymers. (C) 1998 Elsevier Science Ltd. All rights reserved.