Structure and properties of hydrogen and covalently bonded side group liquid crystalline block copolymers

Diblock copolymers incorporating liquid crystallinity via a lateral attachment of mesogenic species to a flexible backbone were studied for their microstructure-property relationships. Two families of materials were studied, distinguished primarily by the method of attachment of the mesogen to the polymer. In the first, azobenzene based mesogens were covalently tethered to the isoprene blocks of a poly(styrene)-block-poly(isoprene), P(S-b-ILC), series of diblock copolymers. In the second family of polymers, hydrogen bonding was used to complex bi-phenyl based mesogens to the acrylic acid units of a poly(styrene)-block-poly(acrylic acid), P(S-b-AA) diblock copolymer. The morphology of the P(S-b-ILC) system was characterized as a function of composition, and clear correlations between the microphase separated structure and the thermal properties of the liquid crystalline mesophase were observed and accounted for. Control of the hierarchical structure in these materials was pursued and achieved independently via surface epitaxy, oscillatory shear and, for the first time in this class of materials, via magnetic fields. It was found that the morphology adopted by the material under the external fields is strongly dependent on the orientation of the liquid crystalline mesophase with respect to the inter-material dividing surfaces present due to the microstructure. Oscillatory shear of a P(S-b-ILC) resulted in the first observation of a novel transverse cylindrical microdomain morphology in one case. The investigation of hydrogen-bonded side-group liquid crystalline block copolymers based on P(S-b-AA) followed a screening of several other candidate host diblock-mesogen pairs. The structure and thermal properties of a model P(S-b-AA) diblock and a homopolymer acrylic acid complexed with mesogens were studied and characterized as a function of composition. A high molecular weight analogue, based on poly(styrene)-block-poly(methacrylic acid), P(S-b-MAA), was successfully

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Osuji, Chinedum, 1976-

Advisor dc:contributor.advisor

• Edwin L. Thomas.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/29973

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/29973