Use of the RAFT technique as an efficient method to synthesise well defined polymer-clay nanocomposites with improved properties
Date
2009-03
Authors
Samakande, Austin
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
Synthesis and structural characterization of two novel cationic and three new neutral
reversible addition–fragmentation chain transfer (RAFT) agents is described. The
cationic RAFT agents bear a quaternary ammonium group: N,N-dimethyl-N-(4-
(((phenylcarbonothionyl)thio)methyl)benzyl)ethanammonium bromide (PCDBAB) and
N-(4-((((dodecylthio)carbonothioyl)thio)methyl)benzyl)-N,N-dimethylethanammonium
bromide (DCTBAB). The three neutral RAFT agents synthesized are 1,4-
phenylenebis(methylene)dibenzene carbodithioate (PCDBDCP), didodecyl-1,4-
phenylenebis(methyllene)bistrithiocarbonate (DCTBTCD) and 11-(((benzylthio)carbonothioyl)
thio)undecanoic acid (BCTUA). The self-assembly behaviour in diluted
aqueous solutions of the cationic RAFT agents, PCDBAB and DCTBAB, is
described. The self-assembly behaviour was promoted by the presence of the thiocarbonyl-
thio group on the RAFT agents, in addition to the overall chemical structure
of the surfactant that also influence self-assembly.
The RAFT agents were used for the bulk or miniemulsion RAFT-mediated controlled
free-radical polymerization in the presence of clay to yield polymer–clay
nanocomposites (PCNs). Bulk polymerization resulted in PCNs with better control of
molar mass and polydispersity index (PDI) values when compared to PCNs prepared
by miniemulsion polymerization. In both bulk and miniemulsion polymerizations the
molar masses and PDI values were dependent on the amount of clay and RAFT
agent present in the system.
Free-radical bulk neutral RAFT agent-mediated polymerization resulted in PCNs with
predominantly intercalated morphology. This was attributed to radical–radical
coupling of the initiator anchored onto the clay galleries on which polymerization took
place. On the other hand, when the cationic RAFT agent anchored onto clay, i.e.
RAFT-modified clay was used, bulk polymerization resulted in predominantly exfoliated PCNs. However, miniemulsion polymerization carried out in the presence
of the RAFT-modified clays resulted in PCNs with a morphology that ranged from
partially exfoliated to intercalated morphology, as the clay loading was increased.
The changing morphology for miniemulsion-based PCNs was attributed to the
decreasing molar mass as the clay loading was increased.
The PCNs obtained had enhanced thermo-mechanical properties as a result of the
presence of clay. The thermo-mechanical properties depended on the molar mass,
PDI, clay loading, and the morphology of the PCNs.
Description
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2009.
Keywords
Dissertations -- Chemistry, Theses -- Chemistry, Addition polymerization, Nanostructured materials, Polymer clay, Polymeric composites