Title page for ETD etd-08012012-040442


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
Abstract
The 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

architectures.

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