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SYNTHESIS OF CYCLIC AND MULTICYCLIC POLYSTYENES AND THEIR SURFACE FLUCTUATIONS IN MELT POLYMER FILMS

He, Qiming
http://orcid.org/0000-0002-2652-3200
http://rave.ohiolink.edu/etdc/view?acc_num=akron1493720701063113

Abstract Details

, Doctor of Philosophy, University of Akron, Polymer Science.
An efficient method for the synthesis of well-defined cyclic polystyrenes using anionic polymerization, silicon chloride linking chemistry, and metathesis ring closure has been developed. The macrocycle precursor, a,¿-bis(4-pentenyl)polystyrene, was formed by 4-pentenyllithium-initiated polymerization of styrene, coupling of a-pentenylpoly(styryl)lithium (PLi) with dimethyldichlorosilane to form a,¿-bis(4-pentenyl)polystyrene (Mn=4600 g/mol) and reaction of excess PLi with ethylene oxide to facilitate purification. Cyclization of the purified a,¿-bis(4-pentenyl)polystyrene was performed in dichloromethane under mild conditions using a Grubbs catalyst, bis(tricyclohexylphosphine)benzylidine ruthenium(IV) chloride, as metathesis ring-closure agent. In contrast to prior work, no fractionation is required to obtain pure product. Both the divinyl precursor and resulting macrocycle were characterized by size exclusion chromatography (SEC), MALDI-TOF mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). The macrocyle was unambiguously distinguished from its precursor using the fragmentation patterns from tandem mass spectrometry (MS2) experiments. The results showed that the macrocyclic precursor, a,¿-bis(4-pentenyl)polystyrene, was of high purity and that the cyclization was highly efficient. With the further application of anionic polymerization, silicon chloride linking chemistry, and metathesis ring-closure, the synthesis of well-defined 8-shaped polystyrene has also been investigated and the fragmentation patterns of the 8-shaped polystyrene have been revealed for the first time using mass spectrometry. The 4-star-polystyrene precursor was formed by coupling PLi with 1,2-bis(methyldichlorosilyl)ethane and reaction of excess PLi with 1,2-epoxybutane to facilitate purification. Ring-closure reaction of the tetra(4-pentenyl)polystyrene was carried out again in dichloromethane under mild conditions using the Grubbs catalyst as catalytic agent. Both the 4-star-polystyrene precursor and resulting 8-shaped polystyrene were characterized by SEC, NMR and MALDI-TOF MS. MS2 results confirmed the formation of intra isomeric 8-shaped polystyrene with the possible existence of inter 8-shaped polystyrene. To reveal the impact of chain ends on surface relaxation, the surface fluctuations of films of both cyclic polystyrene (CPS) and linear polystyrene (LPS) have been measured using X-ray photon correlation spectroscopy (XPCS). The surface fluctuations of a melt film of CPS manifest confinement effects for a film thickness (14Rg) much larger than that manifested by a melt film of the linear chain analog. This is true both in terms of absolute thickness and thickness relative to chain size, Rg. In fact, the linear analog polymer does not manifest confinement effects even at a thickness of 7Rg. Both types of films have a strongly adsorbed layer at the substrate that plays a role in slowing the surface fluctuations for the thinnest films. This layer is 70% thicker for the cyclic chains than for the linear chains. At the interface with the substrate the packing of the cyclic chains is perturbed much more strongly than is the packing of the linear chains. The surface fluctuations of a melt film of a 6k 8-shaped PS have also been measured for comparing chain ends and junction points on the dynamic behaviors. Both the viscosities derived from surface fluctuation and rheological measurements manifest a lower value than the 4-star-polystyrene analog when the temperature is approaching glass transition temperature, Tg,bulk. Comparison among different chain topologies shows the effect of the number of chain ends and junction point on the viscosity. The viscosity behavior of an 8-shaped PS is quite different from that of star analog, but similar to that of the simple cycle analog. The fragility of the 8-shaped molecule in the thin film is reduced relative to that in the bulk, manifesting a nanoconfinement effect which is stronger than for the linear, cyclic, or star architectures.
Mark Foster (Advisor)
Roderic Quirk (Advisor)
Mesfin Tisge (Committee Chair)
Ali Dhinojwala (Committee Member)
Chrys Wesdemiotis (Committee Member)
David Simmons (Committee Member)
Polymer Chemistry

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Citations

  • He, Q. (2017). SYNTHESIS OF CYCLIC AND MULTICYCLIC POLYSTYENES AND THEIR SURFACE FLUCTUATIONS IN MELT POLYMER FILMS [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493720701063113

    APA Style (7th edition)

  • He, Qiming. SYNTHESIS OF CYCLIC AND MULTICYCLIC POLYSTYENES AND THEIR SURFACE FLUCTUATIONS IN MELT POLYMER FILMS. 2017. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1493720701063113.

    MLA Style (8th edition)

  • He, Qiming. "SYNTHESIS OF CYCLIC AND MULTICYCLIC POLYSTYENES AND THEIR SURFACE FLUCTUATIONS IN MELT POLYMER FILMS." Doctoral dissertation, University of Akron, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493720701063113

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.