Type of Document Master's Thesis Author Wood, Paul A. III URN etd-08012012-040442 Title Synthesis and characterization of linear and star-branched butadiene-isoprene block copolymers and their hydrogenated derivatives Degree Master of Science Department Chemistry Advisory Committee
Advisor Name Title McGrath, James E. Committee Chair Mason, John G. Committee Member Wolfe, James F. Committee Member Keywords
- Block copolymers
Date of Defense 1988-09-05 Availability restricted AbstractThe principal purpose of this investigation was to
synthesize and hydrogenate well—characterized linear and
star—branched block copolymers based on butadiene and
isoprene. Sequential anionic addition techniques initiated
by homogeneous organolithium species in hydrocarbon solvents
were employed to prepare several series of butadiene-isoprene
copolymers varying in block size and architecture.
Linear A—B—A poly(butadiene—isoprene—butadiene) triblock
copolymers were synthesized by two different living addition
techniques, e.g., three—stage process using a monofunctional
anionic initiator and a two—stage process using a
difunctional anionic initiator. Alternatively, the synthesis
of star block copolymers involved the sequential
polymerization of poly(butadiene—isoprene) diblock arms which
were then linked into stars via divinylbenzene.
Hydrogenation of unsaturated polymers has widely
attracted attention since this provides an alternate method
for improving and optimizing the mechanical, thermal,
oxidative and chemical resistance properties of these
technological important materials.
Homogeneous catalytic hydrogenation was employed to
chemically modify these linear and star-branched copolymer
into thermoplastic elastomers. Hydrogenation successfully
converted the soft polybutadiene blocks into hard
semicrystalline polyethylene segments, while the central
polyisoprene blocks resulted in the formation of amorphous
alternating rubbery copolymers of propylene-ethylene. The
hard semicrystalline blocks form morphological domains that
serve as physical crosslinking and reinforcement sites.
The presence of semicrystalline segments in both the
linear and star—branched copolymers has important
significance for processing. Above the endothermic melting
temperature of the semicrystalline end. blocks, the now
amorphous system can approach the melt behavior of a singlephase
melt, that is, displaying negligible "physical" network
structure in the melt. Overall, these systems display a
valuable combination of good melt processability together
with physical properties characteristic of A-B—A
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