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Synthesis and Characterization of Surface Relaxations of Macrocyclic Polystyrenes and Interfacial Segregation in Blends with Linear Polystyrenes

Wang, Shih-fan
http://rave.ohiolink.edu/etdc/view?acc_num=akron1322506008

Abstract Details

2011, Doctor of Philosophy, University of Akron, Polymer Science.
The effects of a topology with no chain ends on interfacial segregation in binary polymer blends and the surface fluctuations of films of macrocycles were studied using well-defined macrocyclic polystyrenes (CPS) blended with analog, linear polystyrenes (LPS). A series of well-defined CPSs (Mn = 2,800; 8,600; 17,000; 38,000 g/mol) were synthesized using a combination of anionic polymerization and ring closure metathesis reactions. The macrocyclic polymers were uniquely characterized by Matrix Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) using peaks that were characteristically 28 m/z units less than those of the corresponding precursor peaks, due to the loss of an ethylene unit. The preferential segregation of one component to the air/ polymer and polymer/ substrate interfaces of macrocyclic/ linear blend films of 2k or 37k chains was studied by Surface MALDI-TOF MS (SMALDI-TOF MS), Static TOF Secondary Ion Mass Spectrometry (STOF-SIMS), and Neutron Reflectometry (NR). Blends of bulk composition with 20 wt% of the hydrogenous species were studied. The isotopic effect is not significant for the 2k blends and the chain architecture plays an important role in determining the surface segregation. Measurements with three complementary techniques show the linear species to be enriched at the surface, counter to a self-consistent field theory that considers only the conformational entropic effect of eliminating chain ends. A iv Wall-PRISM theoretical treatment that accounts will for packing effects close to a wall, does, however, correctly predict the surface enrichment by linear chains for a blend of short linear and short cyclic chains. In the case of 37k macrocyclic/linear blends the macrocyclic polymer enriches both the surface and the substrate interfaces, and the surface excess is comparable with the prediction of a modified SCF theory. Surface flucturations of melt films of unentangled CPS with Mn = 2k, 7k, and 14k g/mol were probed using X-ray photon correlation spectroscopy (XPCS). A hydrodynamic continuum theory (HCT) of thermally stimulated capillary waves with a nonslip boundary condition that is adequate for rationalizing the surface fluctuations of linear chain melts also is appropriate for describing the surface relaxation behavior of the CPS films, so long as the film is sufficiently thick. For CPS films thinner than 10 Rg, the universality expected by the theory is no longer seen, suggesting the presence of some confinement effect. The surface fluctuations of the CPS films are slower than those of comparable films of linear polystyrene (LPS) analogs, at a given temperature, due to the higher glass transition temperature of the cyclic analog. As the Tg's of the cyclic and linear analogs approach one another at higher molecular weights, the discrepancy disappears. Film viscosities inferred from the XPCS measurements assuming applicability of the HCT match values obtained from bulk rheology, suggesting that the whole chain dynamics probed in bulk rheometry are what dictate the surface height fluctuation dynamics as well. When normalized surface relaxation rates are considered as a function of dimensionless temperature, T/Tg, a universal temperature behavior is observed for the linear and cyclic chains of all three molecular weights.
Mark D. Foster, Dr. (Advisor)
Ali Dhinojwala, Dr. (Committee Member)
Roderic P. Quirk, Dr. (Committee Member)
Chrys Wesdemiotis, Dr. (Committee Member)
Alamgir Karim, Dr. (Committee Member)
273 p.
Polymers
macrocyclic polystyrene; surface segregation; surface dynamics; SMLADI-TOF MS; Static TOF Secondary Ion Mass Spectrometry; Neutron Reflectometry; X-ray photon correlation spectroscopy

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Citations

  • Wang, S.-F. (2011). Synthesis and Characterization of Surface Relaxations of Macrocyclic Polystyrenes and Interfacial Segregation in Blends with Linear Polystyrenes [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1322506008

    APA Style (7th edition)

  • Wang, Shih-fan. Synthesis and Characterization of Surface Relaxations of Macrocyclic Polystyrenes and Interfacial Segregation in Blends with Linear Polystyrenes. 2011. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1322506008.

    MLA Style (8th edition)

  • Wang, Shih-fan. "Synthesis and Characterization of Surface Relaxations of Macrocyclic Polystyrenes and Interfacial Segregation in Blends with Linear Polystyrenes." Doctoral dissertation, University of Akron, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1322506008

    Chicago Manual of Style (17th edition)

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