Well‐healed: Polymers cross‐linked with trithiocarbonate (TTC) units were prepared by a RAFT polymerization. The repeatable self‐healing systems or macroscopic fusions were accomplished by UV irradiation of the cross‐linked polymer in solution and in the bulk state. The macroscopic fusion of completely separated parts was successful (see pictures, BA=n‐butyl acrylate).

Self-healing polymeric materials with branched architectures and reversible cross-linking functionalities at the periphery of branches were synthesized by atom transfer radical polymerization (ATRP). Poly(n-butyl acrylate) grafted star polymers were prepared by chain extension ATRP from cross-linked cores comprised of poly(ethylene glycol diacrylate). These polymers were further used as macroinitiators for the consecutive chain extension ATRP of bis(2-methacryloyloxyethyl disulfide) (DSDMA), in which way disulfide reversible cross-links (SS) were introduced at the branch peripheries. The SS cross-linked polymers were then cleaved under reducing conditions to form thiol (SH)-functionalized soluble star polymers. The SH-functionalized star polymer solutions were deposited on silicon wafer substrates and converted to insoluble SS re-cross-linked films via oxidation. The self-healing of prepared polymer films was studied by continuous atomic force microscopy (AFM) imaging of cuts micromachined with the AFM tip and by optical microscopy. The re-cross-linked star polymer (X3) showed a rapid spontaneous self-healing behavior, with the extent of healing dependent on the initial film thickness and the width of the cut. The self-healing behavior observed for this sample was attributed to the regeneration of SS bonds via thiol–disulfide exchange reactions. This study demonstrated the suitability of grafted multiarm polymer architectures as building blocks of self-healing polymeric materials and pointed to the importance of low intrinsic viscosity of material and high accessibility of functional groups responsible for healing.

Dimethacrylate trithiocarbonate was synthesized and used as a dynamic covalent cross-linker to prepare PMMA and PSt gels via radical polymerization. The swelling properties of the PMMA gels were studied and showed that in the presence of radicals the gels reorganize to accommodate forces generated by the swelling processes. This reshuffling of the cross-link network yields an increase in the swelling ratio (up to 300% increase) of the PMMA gels. Two different radical generators, a thermal initiator and a CuI/L complex, were successfully used to trigger the reorganization of the gels. To illustrate the broad utility of the procedure, three discrete pieces of gels were fused into one single piece to demonstrate that dynamic covalent cross-linkers can be used to prepare materials that can be reprocessed and/or undergo self-repair.

A poly(n-butyl acrylate)-based star polymer, polyEGDA-(polyBA) n , was synthesized by atom transfer radical polymerization using a modified core-first method. Further polymerization of a disulfide (SS) cross-linking agent bis(2-methacryloyloxyethyl) disulfide from the arm end produced a SS cross-linked star polymer. The disulfide functionality could be cleaved via reducing reactions, generating individual stars containing SH groups at the chain ends. The transformation between SS cross-linked star and SH-star was reversible via repetitive reduction and oxidation. Dynamic light scattering measurements showed that the average diameter of the cleaved star polymer was around 20 nm. The dynamic mechanical properties of these star copolymers were characterized through examination of the temperature dependencies of their shear moduli. The results showed that SS-functionalized star polymers respond to reduction−oxidation conditions, indicating that the disulfide bonds do cleave and re-form. These stimuli responsive star polymers have potential utility as intelligent polymeric materials such as self-healing materials.

Gut geheilt: Mit Trithiocarbonat(TTC)‐Einheiten vernetzte Polymere wurden durch RAFT‐Polymerisation hergestellt. Die selbstheilenden Systeme oder makroskopischen Zusammenschlüsse entstanden bei UV‐Bestrahlung des vernetzten Polymers in Lösung und im Festkörper. Es gelang sogar der Zusammenschluss vollständig getrennter Teile (siehe Bilder, BA=n‐Butylacrylat).

No abstract

MFI type galloaluminosilicates (GaAlMFI) were coated with inert silicalite-1 layers. The silicalite-1 coating could improve the para-selectivity for xylene production in aromatization of propane. In the silicalite-1 coating step, low alkali concentration in the synthesis solution enhanced para-selectivity. A proton-exchange procedure also had an impact on the para-selectivity. Significant decrease of para-selectivity was observed over the silicalite-1 coated GaAlMFI with repeated proton-exchange. From the 71 Ga and 27 Al MAS NMR measurements, demetalation occurred during the proton-exchange process, and those metal species is likely to become catalytically active sites without para-selectivity. From the aromatization of propane and n-butane, para-selectivity in n-butane aromatization was found to be higher than that in propane aromatization. From the product distribution, naphthalene and its derivatives were easier to be produced in propane aromatization compared to n-butane aromatization. The formation of naphthalene and its derivatives may relate to decrease in the para-selectivity in propane aromatization.

7-Ethynylcycloheptatriene (1) cleanly isomerizes to phenylallene in the presence of acid. A mechanism involving the protonation of ethynylnorcaradiene, which is in equilibrium with 1, followed by the cleavage of a three-membered ring to give an arenium ion, is proposed. The rearrangement is accelerated by a factor of 370 by introducing tert-butyl groups on C-2 and C-5, indicating the importance of the equilibrium concentration of the norcaradiene form as a rate-controlling factor.