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We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes, and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η0,linear to their ring counterparts η0,ring at isofrictional conditions is discussed as a function of the number of entanglements Z. In the unentangled regime η0,linear/η0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η0,linear/η0,ring = 2. In the entanglement regime, the Z-dependence of ring viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1 < Z < 20, η0,linear/η0,ring Z1.2±0.3, is weaker than the scaling prediction (η0,linear/η0,ring Z1.6±0.3) and the simulations (η0,linear/η0,ring Z2.0±0.3). Nevertheless, the present collection of state-of-the-art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year-old problem.

We have demonstrated directed self-assembly of poly(styrene-b-dimethylsiloxiane) (PS-b-PDMS) down to sub- 10-nm half-pitch by using grating Si substrate coated with PDMS. The strong segregation between PS and PDMS enables us to direct the self-assembly in wide grooves of the grating substrate up to 500 nm in width. This process can be applied to form various type of sub-10-nm stripe pattern along variety of grating shape. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2297-2301, 2010

The equilibrium properties of polymer brushes formed by starlike polymers with varying number of arms attached to a surface by their center were studied experimentally with neutron reflectrometry (NR). Polystyrene (PS) stars in a good solvent (toluene) were centrally adsorbed onto a quartz substrate via a zwitterionic anchor group. Increasing the number of arms resulted in significantly lower equilibrium adsorbance, while replacement experiments of a 3-armed star brush by linear chains revealed interesting equilibrium and kinetic features related to the special architecture of star polymers. These results are compared with scaling theoretical calculations and Monte Carlo simulations of centrally adsorbed star polymers that were performed under the bond fluctuation simulation scheme. Several features of the experimental results are reproduced in our simulation study.

The complexation between narrow molecular weight distribution poly(2-vinylpyridine) (P2VP) and polystyrene (suPS) or polyisoprene (suPI) end-functionalized with one sulfonic acid group was examined in tetrahydrofuran dilute solutions by a combination of static and dynamic laser light scattering. Both apparent weight-average molecular weight (M w,app ) and hydrodynamic radius (R h ) of the complexes exhibited a maximum at a certain molar ratio of suPS chains to P2VP monomeric units. This indicated that the P2VP backbone may be saturated by the grafted end-functionalized chains because of repulsion between the grafted chains. By changing the molar mass of P2VP from 100,000 to 30,000 g/mol, the values of M w,app and R h decreased. When suPI was used instead of suPS, similar trends were observed. In the latter case, it was possible to prepare block copolymer-like micelles by transferring the P2VP/suPI blend solutions in decane, which is a selective solvent for PI. The non-covalent-bonded polymeric micelle characteristics were investigated as a function of sulfonic acid/2-vinylpyridine units ratio as well as temperature.