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 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 rings 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

Two series of ω-functionalized diblock copolymers polystyrene-b-polyisoprene, PS-PI, having hydroxyl end groups either at the PS (PI-PS-OH) or at the PI (PS-PI-OH) block were synthesized by living anionic polymerization. The samples had similar molecular weights but different compositions. Employing suitable post-polymerization reactions the hydroxyl groups were transformed to the corresponding 2-ureido-4-pyrimidinone (UPy) functions. The UPy group is known to dimerize strongly in a self-complementary array of four cooperative hydrogen bonds. The micellization properties of the unfunctionalized and the ω-functionalized polymers having either hydroxyl or UPy end groups were studied in n-decane, which is a selective solvent for the PI block, by static and dynamic light scattering and dilute solution viscometry. A distinct micellar behavior was obtained depending on the nature of the end group and their location either at the core-forming or the corona-forming block. To confirm the results regarding the effect of the hydrogen bonds the solid-state properties of the copolymers were studied by differential scanning calorimetry and thermogravimetric analysis. Furthermore, the dilute solution properties were investigated in chloroform, which is a common good solvent for both the PS and PI blocks but nonpolar, thus allowing the formation of hydrogen bonds.

The strong influence of (1,3‐phenylene)bis(3‐methyl‐1‐phenyl pentylidene)dilithium initiator (DLI) concentration on the modality of polybutadiene (PBd) in the presence of lithium s‐butoxide (s‐BuOLi) in benzene, at room temperature, has been studied. The quality of DLI has been evaluated by gas chromatography‐mass spectrometry (GC‐MS) and 1H NMR. Keeping s‐BuOLi/C‐Li ratio (R) close to unity, at relatively high DLI concentrations (C > 7 × 10−4 M), monomodal high 1,4‐PBds with polydispersity index less than 1.07 were obtained, whereas bimodal ones at lower concentrations (C < 6 × 10−4 M). The effect of C‐Li concentration on the modality of PBd has been evaluated using size exclusion chromatography on samples taken during and at the end of the polymerization. Viscosity observations have also been used to further support the results. The bimodality of PBd has been attributed to partially terminated difunctional species because of the inevitable presence of protic impurities in the polymerization solution, although high vacuum technique was used, which becomes more significant at low initiator concentrations. Moreover, the strong influence of s‐BuOLi on the microstructure of PBd has been demonstrated by 1H NMR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

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