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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The morphological behavior of miktoarm star and multiple-graft block copolymers

Beyer, Frederick Louis 01 January 1999 (has links)
The effects of molecular architecture on block copolymer morphological behavior for two distinct types of architectures have been investigated. The first, AnBm-type stars, have a single, centrally located junction point from which blocks of two polymer species radiate, and are referred to as miktoarm stars. The extremes of a model proposed by Milner were investigated using three miktoarm systems, A2B2 stars, A8B 8 “Vergina” stars, and A5B stars. Samples having a low molecular asymmetry agreed in general with the predictions of this model, although bicontinuous morphologies were not observed. The A5B miktoarm samples, which have a high level of molecular asymmetry, exhibited behavior not predicted by the model, but which was consistent with a trend of discrepancies observed in prior studies. The effect of the junction point on chain stretching behavior in miktoarm stars was noted by comparing the lamellar period of several A2B2 and A8B8 stars to comparable AB diblocks. These materials were found to have significantly increased lamellar periods, thought to result from the increased chain stretching at and near the junction point. The second type of molecular architecture investigated was the multiple-graft architecture. Three series of multigrafts, were characterized: regular multigrafts with tetrafunctional branch points, random multigrafts with trifunctional branch points, and random multigrafts; with tetrafunctional branch points. Using the constituting block copolymer hypothesis, the behavior of these molecules was predicted using existing theories for block copolymers with simpler architectures. Use of this hypothesis is justified herein, and illustrates that the behavior of block copolymers with complex architectures is dictated by the preferred behavior of smaller architectural subunits from which the multigraft is comprised. The morphological behavior of multiple-graft block copolymers was shown to be influenced by branch point functionality, branch point location, and the number of branch points per molecule. Architectural heterogeneity was found to impair self-assembly behavior of the multigrafts. Small-angle scattering data indicating the formation of microphase separated domains of specific shapes were observed for non-lamellar morphologies, which are able to form and fill space without ordering on a lattice. Finally, lamellar grain size and shape a the series of regular multigrafts was investigated. Grain size was seen to be influenced by the total molecular weight of the multigraft. Grain anisotropy was found to increase as the lamellar grains increase in size, indicating that the growth of lamellar grains is anisotropic, occurring more readily in the direction normal to the plane of the lamellae.

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