Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.

(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)

Miktoarm star block copolymers: Effects of molecular architecture over morphology

Lizhang Yang, University of Massachusetts Amherst


Three aspects of the effects of molecular architecture on block copolymer and block copolymer/homopolymer blends morphological behavior have been investigated. In the Chapter 2 and 3, the morphological behaviors of “Model” graft block copolymer/homopolymer blends was discussed. The morphological behaviors for two distinct types of graft architectures were investigated. The first type, I2S block copolymers, which have 2 low polydispersity (PDI) polyisoprene arms and one low PDI polystyrene arm joint at a single junction point, has an asymmetry, non-linear molecular architecture. The second type, I2S2 block copolymers, which have 2 low PDI polyisoprene arms and two low PDI polystyrene arms joint at a single junction point, has a symmetry, non-linear molecular architecture. In the blend study, a slow co-casting procedure was developed to get single crystal structure of Gyroid morphology. The amazing scattering patterns of this sample provide the best evidence for Gyroid morphology observed so far. In Chapter 4, morphological behavior of I5S block copolymers was studied to investigate the systematic discrepancies between the theoretical predicated miktoarm star block copolymer morphology and the experimental observations. The current results indicate that geometrical packing constraints prevent the formation of morphologies such as spheres and cylinders in highly asymmetric miktoarm stars in which the minor volume fraction component would need to occupy the matrix phase. Unusual broken chevron tilt grain boundary morphologies were also observed in a lamellar I5 S material. We attribute these new structures to the asymmetric energy penalties for interfacial bending which result from the molecular asymmetry of the miktoarm stars. Finally, irreversible morphology transformation from lamella to cylinder was investigated using selective solvent approach. Selective solvent can preferentially swell one of the components of block copolymers, increase the effective volume fraction of that component during solvent casting and thus affect the resulting block copolymer morphology. During the subsequent annealing, the kinetically trapped unstable morphology will transform to its stable morphology. By controlling the annealing temperature and the length of annealing time, we will be able to tract the detailed information about the morphology transformations.

Subject Area

Chemical engineering|Plastics|Polymers

Recommended Citation

Yang, Lizhang, "Miktoarm star block copolymers: Effects of molecular architecture over morphology" (2002). Doctoral Dissertations Available from Proquest. AAI3039404.