Degree Type

Dissertation

Date of Award

1990

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Thomas J. Barton

Abstract

Several new types of silicon-containing preceramic polymers, i.e., poly(diorganosilacetylene) and poly(diorganosilvinylene) have been synthesized with molecular weights from 10,000 to 120,000. These polymers could be thermally converted to SiC with a moderate to high char yields. Ready solubility and good processability made these types of polymers even more attractive in their applications to ceramics;First example of copolymer which contains alternate -SiMe[subscript]2-C≡C- and -SiMe[subscript]2-CH=CH- units was successfully synthesized. This copolymer had a dramatically lower decomposition temperature (300°C) and high char yield;The thermal polymerization of diethynyldiphenyl-silane, which was reported in 1968 to afford poly(diphenylsildiacetylene) (Ph[subscript]2Si-C≡C-C≡C)[subscript] n via dehydrogenation, was reinvestigated. Spectroscopic studies showed that the polymer had a structure of polyacetylene type not diacetylene;Diphenyldiethynylgermane and a series of diorganodiethynylsilanes were synthesized. These diethynyl- silane or germane could be polymerized in the presence of MoCl[subscript]5 or WCl[subscript]6 to afford a soluble, violet material with Mw as high as 108,000 (PDI ca. 2). The violet polymer was found to have a four-membered ring structure from cyclopolymerization of diorganodiethynyl-silane monomer. The polymer was intrinsically an electrical insulator. Brief exposure of the polymer film to I[subscript]2 vapor could increase the conductivity up to 0.1 s/cm. The non-linear [chi][superscript](3) value at 625 nm was measured to be 3 x 10[superscript]-9 esu, one of the largest measured among [pi]-conjugated polymers. Photobleaching recovery at 2 ev, measured with 75 fsec resolution, was 300 femtosecond (3 x 10[superscript]-13 second) which is the fastest ever observed in the [pi]-conjugated polymers;As a structural model study for cyclopolymerization of 1,6-heptadiyne, bis(ethynyldimethylsilyl)methane was polymerized by using MoCl[subscript]5 or WCl[subscript]6 catalyst to afford a red polymer with UV [lambda][subscript] max 440 nm. The structure of the polymer was first confirmed spectroscopically as a six-membered ring.

DOI

https://doi.org/10.31274/rtd-180813-11105

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Yi Pang

Language

en

Proquest ID

AAI9110551

File Format

application/pdf

File Size

244 pages

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