Title

Photopolymerization In Liquid Crystalline Media: Development of Nanostructured Polymeric Materials

Date of Award

2002

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

C. Allan Guymon

Advisor Department

Polymers and High Performance Materials

Abstract

This work focuses on understanding the processes involved in the development of polymer nanostructure in liquid crystalline media. Through understanding the processes governing nanostructured polymer development, the ability to controllably synthesize nanostructured polymeric materials will be gained. Polymerization kinetics were studied for a variety of monomers photopolymerized in a smectic liquid crystal. Interestingly, a substantial increase in polymerization rate is observed as LC order increases for all monomers studied due to ordering effects of the LC. This rate acceleration is particularly pronounced for a fluorinated monoacrylate monomer. The fluorinated monoacrylate remains segregated between the smectic layers of the LC before, during and after polymerization, while other polymers phase separate. The linear fluorinated polymer is also ordered after polymerization leading to continued birefringence in the polymer/LC samples at elevated temperatures. When applied to a ferroelectric liquid crystalline (FLC) system, retention of the FLC electro-optic properties is observed in polymer/FLC systems with linear fluorinated polymer incorporated while properties are retarded in systems with an aliphatic polymer incorporated. The order of the LC may not only affect the polymerization rate and polymer nanostructure, but affects polymer molecular weight as well. Chain transfer to the LC was found to play a critical role in the observed effects on polymerization rate and molecular weight LC solvent systems. Nanostructure development for lyotropic liquid crystal systems was examined through the photopolymerization of non-mesogenic acrylate monomers in Pluronic LLC media. The mesophase thermal stability of a polymer/LLC sample is directly related to the polymer nanostructure that forms. Polymer nanostructures generated in the continuous regions of the LLC mesophase impart more thermal stability than polymers formed in LLC discontinuous regions. When copolymer systems of water and oil soluble monomers are examined, mesophase thermal stability depends heavily on the copolymer ratio. The physical properties of the polymers resulting from the homopolymer and copolymer polymerization were examined. The polymer physical properties are greatly dependent on the LLC phase in which the polymers are synthesized in on the copolymer ratio used. (Abstract shortened by UMI.)