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Synthesis and Surface Fluctuations of Cyclic Polystyrenes and Their Interfacial Segregation in Blends with Linear Polystyrenes

He, Qiming
http://orcid.org/0000-0002-2652-3200
http://rave.ohiolink.edu/etdc/view?acc_num=akron1376063972

Abstract Details

2013, Master of Science, University of Akron, Polymer Science.
A well-defined cyclic polystyrene (CPS, Mn = 6,000 g/mol) was synthesized using a combination of anionic polymerization and metathesis ring closure. A new synthetic route was developed to produce CPS (Mn = 4,600 g/mol) with higher yield using anionic polymerization, linking chemistry and metathesis ring closure. The formation of cyclic polystyrenes was accurately characterized using Matrix Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-ToF MS). The monoisotopic peaks at values of m/z that were 28 units less than those of the corresponding precursor peaks are characteristic of cyclization. These peaks appear due to the elimination of an ethylene molecule during the cyclization reaction. The interface segregation of binary blends of cyclic and linear polystyrenes with similar molecular weights was investigated using Neutron Reflectometry (NR) to determine the chain molecular weight at which the segregation behavior crosses over from a behavior characteristic of low molecular weight blends, for which the linear chain is preferred at the surface, to a behavior characteristic of high molecular weight blends, for which the macrocyclic chain is preferred at the surface. The enrichment of one component at both the air/polymer and polymer/substrate interfaces of these blend films was studied for chains of molecular weight 2k, 6k and 16k. The blends were composed of 80 wt% deuterated species and 20 wt% hydrogenous species. In the 2k blends, the isotopic effect is negligible, and surface segregation is dictated by the chain architecture. As the molecular weight increases, the enrichment of the air surface in linear chain becomes weaker, despite the fact that the isotopic effect that tends to drive the perdeuterated linear species to the surface becomes stronger as molecular weight increases. For the 16k blend no enrichment of the blend surface can be resolved with NR measurements, suggesting that at a molecular weight near that value the strength of the driving force for surface enrichment of linear chains due to isotopic labeling is about equal to the driving force for surface enrichment of cyclic chains due to effects of the molecular architecture on the chain packing. Surface fluctuations of melt films of 6k CPS and linear analogs with different thicknesses were measured using X-ray photon correlation spectroscopy (XPCS). The surface fluctuations of the 6k linear melt films thicker than 17 nm and the 6k cyclic melt films thicker than 28 nm can be described by a hydrodynamic continuum theory (HCT). When the film of CPS is thinner than 24 nm, the behavior of the surface fluctuations is no longer captured by the HCT, and the relaxation times are much longer than predicted by the HCT. However, unlike the confinement effect reported for films of entangled linear chains, there is no evidence of an effective modulus in the very thin films of cyclic chains. In the context of the HCT, the behavior of the very thin films can be rationalized by supposing that the films have effective viscosities higher than the bulk value. One possible explanation for this behavior could be an increase in glass transition temperature (Tg) of a CPS film with decreasing thickness for thicknesses below 28 nm. Such a change would be opposite to the change in Tg with thickness seen for linear PS melt films and needs to be experimentally investigated.
Mark Foster, Dr. (Advisor)
Roderic Quirk, Dr. (Committee Member)
Polymers

Recommended Citations

Citations

  • He, Q. (2013). Synthesis and Surface Fluctuations of Cyclic Polystyrenes and Their Interfacial Segregation in Blends with Linear Polystyrenes [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1376063972

    APA Style (7th edition)

  • He, Qiming. Synthesis and Surface Fluctuations of Cyclic Polystyrenes and Their Interfacial Segregation in Blends with Linear Polystyrenes. 2013. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1376063972.

    MLA Style (8th edition)

  • He, Qiming. "Synthesis and Surface Fluctuations of Cyclic Polystyrenes and Their Interfacial Segregation in Blends with Linear Polystyrenes." Master's thesis, University of Akron, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1376063972

    Chicago Manual of Style (17th edition)

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