Morphologies and tensile properties of block copolymers with different molecular architectures

The effects of molecular architecture on morphological behavior of block copolymers for four types of architectures have been investigated. In Chapter 2, the morphological behaviors of a group of polystyrene-polybutadiene (PS-PBD)C cyclic block copolymers and their corresponding linear polystyrene-polybutadiene-polystyrene (PS-PBD-PS) triblock copolymer precursors were investigated across a range of morphologies. The contour length and the volume fraction of the cyclic block copolymers obtained are essentially identical to that of their corresponding linear triblock copolymers. Therefore, morphological difference due to compositional mismatch between the cyclic and triblock copolymer pair is eliminated. It is found that when the cyclic and its triblock copolymer form the same morphology, microdomain periods of cyclic block copolymers are all smaller than those of the corresponding linear triblock copolymer precursors. This is resulted from the portion of chain segments that adopts their trajectory parallel to the interface in cyclic block copolymers and thus does not contribute to domain spacing. When different morphologies are formed between the cyclic and triblock pairs, the interface tends to curve away from the linked end-block side in cyclics compared to their triblock copolymers. In Chapter 3, lamellar spacings of a series of (PS)n(PI) n star block copolymers, with n = 1, 2, 4, 16, were studied. Among the series, all the PS blocks are of same length and all the PI blocks have the same molecular weight. Lamellar spacings of the stars (n = 2, 4, 16) were compared directly with that of the diblock copolymer (n = 1). A significant increase in lamellar spacing with increasing junction point functionality (n) was found in this series of materials and can be attributed to molecular crowding near the junction point. Chapter 4 and chapter 5 discussed the effect of chain architecture on the morphological and tensile properties of series of multigraft copolymers. By applying the “constituting block copolymer concept”, the physical behavior of these molecules was compared with the existing theories. It is found that morphological behavior of grafted copolymers can be well predicted using this theoretical approach. The material property, however, is controlled by both the chain architecture and the morphologies thus formed