Rheo-Optical Near-Infrared (NIR) Characterization of Styrene-Butadiene Rubber (SBR) Using Two-Trace Two-Dimensional (2T2D) Correlation Analysis.

A rheo-optical characterization technique based on the combination of near-infrared (NIR) spectroscopy and tensile testing was applied for the first time to an actual rubber sample based on styrene-butadiene rubber (SBR) including silica filler. When SBR samples were subjected to mechanical deformation, changes in the NIR spectral features were readily captured. Two-trace two-dimensional (2T2D) correlation analysis was then applied to the sets of NIR spectra to clearly reveal the subtle but pertinent difference between the NIR spectral features of the initial and deformed SBR. The initial deformation of the sample induces greater deformation of the soft butadiene groups than of the hard styrene groups. The inclusion of the silica filler and a coupling agent (CA) essentially develops firm links between the silica and butadiene via the CA to restrict the displacement of the butadiene during the tensile deformation of the system. The development of such linkage requires even more mechanical force to deform the SBR, which, in turn, improves Young's modulus of the rubber system. Asynchronous correlation spectra of SBR with no silica filler revealed that, during the deformation of the SBR, the butadiene groups were initially deformed, and this feature was then replaced by the predominant deformation of the hard styrene groups. On the other hand, this correlation feature became somewhat unclear when a similar analysis was applied to the SBR sample with silica filler, revealing subtle differences in interaction between individual comonomer functional groups distributed randomly along the copolymer chain and CA.

Insights into the cavitation morphology of rubber reinforced with a nano-filler.

Notwithstanding the various uses of rubber, the fracture mechanism of filler-reinforced rubber remains unclear. This study used four-dimensional computed tomography (4D-CT) involving monochromatic synchrotron X-rays to examine the cavitation within silica-reinforced rubber quantitatively and systematically. The results suggested a threshold value of silica content for the cavitation morphology. Macroscopic fractures, such as those developed by void formation, occurred below the threshold value of silica content. Above this threshold, the density of rubber decreased but macroscopic voids rarely occurred. The lower-density rubber area in the high-silica-content rubber was reversible at the effective pixel size for 4D-CT. These results suggest that the growth of the damage points to macrosized voids could be stopped by the formation of a network of rigid polymer layers. This study allows the elucidation of the reinforcing mechanism and the cavitation morphology of filler-reinforced rubber.

Anthranilamide (aam)-substituted arylboranes in direct carbon-carbon bond-forming reactions.

Anthranilamide (aam)-substituted arylboranes, which were reported to serve as masked boranes in the Suzuki-Miyaura coupling, have been found to be directly cross-coupled just by use of an aqueous medium. The excellent stability of 2-pyridyl-B(aam) toward protodeborylation allowed their smooth cross-coupling.

An anthranilamide-substituted borane [H-B(aam)]: its stability and application to iridium-catalyzed stereoselective hydroboration of alkynes.

A new anthranilamide-substituted borane [H-B(aam)] was synthesized and found to serve as a stable, easy-to-handle substitute for H-B(pin). It was applied to the direct synthesis of diverse linear (E)-alkenyl-B(aam)s via regio- and stereoselective hydroboration of terminal alkynes under iridium catalysis. A boryliridium hydride complex arising from the oxidative addition of H-B(aam) to the Ir catalyst was isolated and characterized via NMR studies.

Anthranilamide (aam)-substituted diboron: palladium-catalyzed selective B(aam) transfer.

An unsymmetrical diboron bearing an anthranilamide (aam) substituent was synthesized and was found to be coupled with aryl halides through the palladium-catalyzed Miyaura-Ishiyama-type reaction. The selective transfer of aam-substituted boryl moiety led to exclusive formation of diverse Ar-B(aam).

Copper-Catalyzed B(dan)-Installing Carboboration of Alkenes.

Carboboration of alkenes was found to occur readily with an unsymmetrical diboron [(pin)B-B(dan)] and alkyl halides under copper catalysis, leading to the direct formation of protected alkylboron compounds via synchronous C-C and C-B bond-forming processes. The B(dan) moiety was solely installed into the organic frameworks with the regioselective attachment to a terminal carbon of alkenes employed.

B(MIDA)-Containing Diborons.

Unsymmetrical B(MIDA)-containing diborons of potential synthetic utility were found to be synthesized from the readily available (neop)B-B(neop) and (HO)2B-B(OH)2, and the procedure was extended to the generation of symmetrical (MIDA)B-B(MIDA). NMR and X-ray crystal structure studies revealed that B(MIDA) units of all of the diborons obtained in this study were in rigid tetrahedral environment.

Silver-catalyzed highly regioselective formal hydroboration of alkynes.

A silver(I)-N-heterocyclic carbene complex has proven to be a potent catalyst for formal hydroboration of alkynes, providing a variety of borylalkenes in regio- and stereoselective manners. Under the silver catalysis, allenes also undergo regioselective hydroboration to give borylalkenes.

Copper-catalyzed three-component carboboration of alkynes and alkenes.

Carboboration of alkynes was found to take place efficiently by a three-component coupling reaction with diboron and carbon electrophiles under copper catalysis to afford diverse multisubstituted borylalkenes in a stereoselective manner. The carboboration was also applicable to alkenes, leading to the formation of multisubstituted borylalkanes via regioselective carbon-boron and carbon-carbon bond-forming processes.