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Morphological studies of graft copolymers with different molecular architectures
The effects of phase behavior and the molecular architecture on morphological behavior of graft copolymers for three types of architectures have been investigated. In Chapter 2, the effects of homopolymer on the formation of T-junction grain boundaries have been studied in a blend of polyisoprene homopolymer and a single graft block copolymer I2S with two equal length blocks of polyisoprene and one arm of polystyrene linked at a common junction point. While T-junctions were previously observed to be quite rare compared to other tilt grain boundary morphologies such as chevrons and omegas, they were found in abundance in the blend used in the current study. Simple free energy calculations show that the homopolymer present in the blend stabilizes the cylindrical curvature of the end caps, rendering the T-junction morphology more stable in blends than in neat block copolymers. This agrees with the observed greater frequency of occurrence of the T-junctions in our blend sample than in neat block copolymers. In Chapter 3, we report the observation of a lyotropic phase transition between the lamellar and cylindrical morphologies in a mixture of polystyrene-polyisoprene Y-shaped single graft copolymer with a lower molecular weight homopolyisoprene. The nature of the intermediate structures which form as the transition progresses has been examined via transmission electron microscopy (TEM) and Wigner-Seitz cell analysis with simple free energy arguments. The shapes of grains of cylindrical morphology have been analyzed via an adaptation of Wulff construction and simple interfacial free energy calculations. In Chapter 4, nucleation of cylindrical morphology at chevron, omega and T-junction grain boundaries is observed in blends of homopolyisoprene and I2S single graft block copolymer in which two arms of polyisoprene (PI) and one arm of polystyrene (PS) are linked at a common junction point. Chapter 5 and Chapter 6 discuss the morphological behavior of organic-inorganic randomly grafted copolymers and trifunctional multigraft copolymers, respectively. By applying the results from the recently established mean-field theory, we study the microphase segregation of organic-inorganic randomly grafted copolymers. For trifunctional multigraft copolymers, "constituting block copolymer concept" is used to understand their morphological behavior.
Burgaz, Engin, "Morphological studies of graft copolymers with different molecular architectures" (2006). Doctoral Dissertations Available from Proquest. AAI3212725.