Rheology and structure change of poly(ether-block-amide) segmented block copolymer

Abstract

Melt of a segmented block copolymer constituting of poly (lauryl lactam) as the hard segment and poly (tetramethylene oxide) as the soft segment was investigated by rheological techniques. Storage modulus of the polymer melt exhibits the non-terminal behavior resembling those of diblock and triblock copolymer melts, indicating the existence of a microphase separated structure. Contrarily to most block copolymers, the melt of the segmented block copolymer transforms from a weak structure to a stiff one upon raising temperature. Atomic force microscopic data in tapping mode reveal that at low temperatures the structure of the melt is constituted of small spherical soft domains dispersed in a hard matrix and the hardness of the matrix differs slightly from that of the domains; at high temperatures the spherical domain structure preserves but the domain becomes larger and so does the hardness difference between the domain and the matrix. Infrared spectrum analysis shows that the temperature induced structural change is related to the dissociation of hydrogen bonding between the hard and the soft segments.