Title page for ETD etd-441222242971820


Type of Document Dissertation
Author Xie, Donghang
Author's Email Address dxie@vt.edu
URN etd-441222242971820
Title Part I: Synthesis and Ring Opening polymerization of Macrocyclic monomers for Production Of engineering Thermoplastics
Degree PhD
Department Chemistry
Advisory Committee
Advisor Name Title
Marand, Hervé L.
McGrath, James E.
Merola, Joseph S.
Gibson, Harry W. Committee Chair
Tanko, James M. Committee member
Keywords
  • Polyrotaxanes
  • Poly(aryl ether)s
  • Macrocycles
  • Synthesis
  • Polymerization
  • Ring opening polymerization
Date of Defense 1997-01-14
Availability unrestricted
Abstract
Part I: Single sized, pure arylene ether macrocycles

ranging from 30 to 60 atom ring sizes were

synthesized in good yields (up to 83%) by the two

component method under high dilution conditions.

These macrocycles have unsymmetric structures

containing sulfone/ketone or sulfone/phosphine oxide

functional groups and have relatively low melting

points. The melt ROP of the single sized macrocycles

to form poly(arylene ether)s exhibits two stage

characteristics: the first stage is very fast, driven by the

large entropy difference between cyclics and linears;

the second stage is very slow and is diffusion

controlled due to the high viscosity created in the first

stage reaction. The latter stage leads to incomplete

polymerization at the low initiator concentrations (1-3

mol%). At high initiator concentrations (5-7 mol%),

100% conversion is reached due to improved initiator

distribution in macrocycles; however, this reduces

molecular weights of the polymers. The molecular

weight is found to build up very rapidly, independent

of conversion, reaction time and type of initiator. The

ROP is initiated by CsF and alkali phenoxides. The

efficiency of the alkali counterion is generally in the

order of Cs+>K+>Na+, while a phenoxide initiator is

more efficient than a fluoride initiator. It is also found

that the Cs counterion leads to highest degree of

crosslinking. The ROP of cyclic oligomeric mixtures is

also reported for comparison; the study shows that

the molecular weight depends on time and conversion,

and that the conversion is sensitive to the content of

linear impurities and the average ring size of cyclic

mixtures.

Part II: Polyrotaxanes are novel polymeric materials

comprised of linear polymer molecules and threaded

macrocycles with no covalent bond between the two

components. With potential movements of the cyclic

component and judicious combinations of the two

components of different properties, these materials

have brought interesting changes of physical

properties, such as morphology, crystallinity,

solubility, viscosity, etc. In this part of the dissertation,

a new family of polyrotaxanes with poly(arylene

ether)s as backbones and crown ethers as cyclic

components are described. These include linear

poly(arylene ether) based polyrotaxanes and

hyperbranched poly(ether ether ketone) based

polyrotaxanes; both are synthesized via aromatic

nucleophilic substitution reactions. Preliminary studies

show that these polymers exhibit great enhancement

of solubility. The polymers form emulsions in water

and methanol which are normally non-solvents for the

poly(arylene ether) backbones. In some cases, they

are even soluble in water to form a clear solution. The

attempted syntheses of polyrotaxanes using aromatic

macrocycles described in Part I was not successful,

with no indication of threading.

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