New sorbents for the desulfurization of liquid fuels were developed using π-complexation. Vaporphase adsorption isotherms were investigated to understand the interaction between benzene/ thiophene and various kinds of sorbents, including Ag-Y, Cu-Y, Na-Y, H-USY, Na-ZSM-5, activated carbon, and modified activated alumina. Compared to Na-Y, Cu-Y and Ag-Y adsorbed significantly larger amounts of both thiophene and benzene at low pressures, as a result of π-complexation with Cu + and Ag + . Molecular orbital calculations confirmed that the relative strengths of π-complexation lie in the order thiophene > benzene and Cu + > Ag + . The experimental heats of adsorption for π-complexation are in excellent agreement with theoretical molecular orbital predictions. Na-ZSM-5 and activated carbon could also adsorb small amounts of thiophene and benzene at low pressures. The sorbent capacities for thiophene at the low pressure of 2.3 × 10 -5 atm were 0.92 molecule/Cu + and 0.42 molecule/Ag + and followed the order Cu-Y and Ag-Y . Na-ZSM-5 > activated carbon > Na-Y > modified alumina and H-USY. The separation factors of thiophene over benzene (at low concentrations of thiophene) calculated from pure component adsorption isotherms exhibited the trend Ag-Y > Na-ZSM-5 > Cu-Y ≈ activated carbon . Na-Y . H-USY ≈ modified activated alumina.

The gel-melting temperatures of branched polyethylene-cyclohexane-carbon disulfide gels were measured. Branched polyethylenes having a different number of long-branching points were used. The reciprocal of the gel-melting temperature is a linear function of the logarithm of the polymer concentration. A theory which predicts the gel-melting temperature of branched crystalline copolymers is given. Analysis of the experimental data suggests that the size of the crystalline junction decreases with an increase in the number of long-branching points. KEY WORDS Sol-Gel Transition I Branched Polyethylene I Gel I Gel-Melting Temperature I Polyethylene I

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A facile approach to polymethacrylate networks that contain thermally exchangeable bis(2,2,6,6-tetramethylpiperidin-1yl)disulfide (BiTEMPS) cross-linkers is reported, and the easily inducible healability and reprocessability of the obtained networks are discussed. The free radical polymerization of BiTEMPS crosslinkers and hexyl methacrylate (HMA) monomers afforded insoluble and colorless networks of poly(hexyl methacrylate) (PHMA) films, whose structures were characterized after de-crosslinking via thermal BiTEMPS exchange reactions with added lowmolecular-weight BiTEMPS. Swelling experiments and stressrelaxation measurements at elevated temperatures revealed the contribution of BiTEMPS as a polymer chain exchanger both in the gels and in the bulk. The BiTEMPS-cross-linked PHMA networks showed damage healability and repeatable reprocessability in the bulk by simple hot pressing at 120 °C under mild pressure (∼70 kPa). These results should grant facile access to various vinyl polymer networks with on-demand malleability.

Intrinsically exchangeable dynamic covalent bonds that can be triggered by readily usable stimuli offer easy incorporation of their dynamic properties in various molecular systems, but the library of such bonds is still being developed. Herein, we report the dynamic covalent chemistry of 2,2,6,6-tetramethylpiperidine-1-sulfanyl (TEMPS) dimers derived from thermally reversible homolytic dissociation of disulfide linkages. High air stability of TEMPS was observed even at 100 °C, affording facile employment of thermal dissociation-association equilibria and adjustable bond exchange properties under atmospheric conditions. We also established an efficient synthetic route for a modifiable derivative of the dimer that enabled incorporation of dynamic properties into linear and network polymer structures. The obtained polymers showed controllable molecular weights, temperature-dependent swelling properties, healing ability, and recyclability, reflecting the thermally tunable dynamics of the dimer.

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