Type of Document Dissertation Author Williamson, David URN etd-09252003-192601 Title SYNTHESIS AND CHARACTERIZATION OF WELL-DEFINED POLY(1,3-CYCLOHEXADIENE) HOMOPOLYMERS AND COPOLYMERS Degree PhD Department Chemistry Advisory Committee
Advisor Name Title Long, Timothy E. Committee Chair Esker, Alan R. Committee Member Kingston, David G. I. Committee Member McGrath, James E. Committee Member Willis, Carl L. Committee Member Keywords
- high molecular weight
- block copolymers
- anionic polymerization
- thermoplastic elastomers
Date of Defense 2003-08-21 Availability unrestricted AbstractPolymers containing poly(1,3-cyclohexadiene) were synthesized using a novel pre-formed initiator comprised of an alkyllithium and a tertiary diamine. The use of a pre-formed intiator at moderate temperatures (25° C) enabled the synthesis of high molecular weight poly(1,3-cyclohexadiene) homopolymers ( = 50000) with narrow molecular weight distributions ( / = 1.20). In contrast, the use of a conventional anionic initiation approach resulted in polymerizations that lacked significant degrees of livingness, which limited the polymer molecular weights to approximately 10000. Use of the preformed initiator resulted in a reduction in the degree of both chain termination and chain transfer. In addition, the livingness of the polymerization was shown to be a function of the monomer concentration and the polymerization temperature. The regiochemistry of the polymers were shown to be dependent on the tertiary amine used in the polymerization, which provided a route for the synthesis of polymers with a microstructure rich in either high 1,2-addition (70%) or high 1,4-addition (90%). A range of analytical methods were employed to determine the stereo and regiochemistry of poly(1,3-cyclohexadiene). These methods included 1H NMR, 13C NMR, and endgroup functionalization of the propagating center with chlorotrimethylsilane. The impact of regiochemistry on the thermal properties was examined using differential scanning calorimetry. In addition, the thermooxidative properties of these poly(1,3-cyclohexadiene) polymers were characterized in a series of oxidative studies and the onset of oxidative degradation occurred at 110° C. Perfectly alternating copolymers of poly(1,3-cyclohexadiene-alt-styrene) were synthesized, and the reactivity ratios for these copolymers (r1,3CHD =
0.022, rstyrene = 0.024) were determined using a conventional Mayo-Lewis approach. The effect of aromatization and hydrogenation on the thermal properties of these copolymers was determined using thermal gravimetric analysis and differential scanning calorimetry. The synthesis of poly(1,3-cyclohexadiene) DVB coupled star-shaped polymers was performed using a convergent arm-first approach in combination with a divinylbenzene coupling agent (PDI = 1.25). Well-defined poly(1,3-cyclohexadiene-block-isoprene)-star shaped polymers were synthesized and utilized for the development of novel high temperature thermoplastic elastomers, with excellent elastomeric properties (percent elongation = 745 %, tensile strength = 7.2 MPa). Atomic force microscopy in combination with differential scanning calorimetry verified the presence of microphase separation between the blocks.
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