Highly crystalline syndiotactic 1,2‐polybutadiene (s‐PB) having melting point (mp) up to 216°C was obtained by using a Co(acac)3‐AIEt3‐CS2 catalyst. The polymer with mp 208°C was found to have 99.7% 1,2 content and 99.6% syndiotacticity by 1H and 13C‐NMR measurements. The s‐PB can be molded by addition of a stabilizer such as 2,6‐di‐t‐butyl‐4‐hydroxymethylphenol into fiber, film, and various shaped articles. The physical properties presented in the present article include stress‐strain and dynamic mechanical behavior. The highly crystalline syndiotactic 1,2‐polybutadiene was applied to a carbon fiber and UBEPOL VCR (cis‐1,4‐polybutadiene reinforced by fibrous syndiotactic 1,2‐polybutadiene).

The thermal crosslinking and loss of vinyl unsaturation of syndiotactic 1, 2‐polybutadiene(s‐PB) at 180–230°C were prevented by stabilizers with 3, 5‐di‐t‐butyl‐4‐hydroxybenzyloxy group. The s‐PB samples (mp 140–198°C and MW 20,000–70,000) that contained the stabilizers could be melt‐spun at a temperature below 220°C into 1‐denier fibers to be used for the preparation of carbon fibers. The s‐PB fibers with higher mp and/or higher MW could be obtained by the addition of a high boiling solvent such as tetralin. The relationship between the molecular structures of s‐PB and the properties of resulting s‐PB fibers, including the degree of molecular orientation measured by birefringence and x‐ray diffraction, is presented. Spun fibers showed small swellings here and there along the fiber axis, which would have resulted from the inhomogeneity of the melt of s‐PB spun at a temperature slightly above the melting point. The gelation was unlikely to occur.

A stimuli-responsible reversible structural transformation is of key importance in biological systems. We now report a unique water-mediated reversible transformation among three discrete double-stranded dinuclear titanium­(IV) achiral meso- and chiral rac-helicates linked by a mono­(μ-oxo) or a bis­(μ-hydroxo) bridge between the titanium ions through hydration/dehydration or its combination with a water-mediated dynamic cleavage/re-formation of the titanium-phenoxide (Ti–OPh) bonds. The bis­(μ-hydroxo) bridged titanium­(IV) meso-helicate prepared from two tetraphenol strands with titanium­(IV) oxide was readily dehydrated in CD3CN containing a small amount of water upon heating, accompanied by Ti–OPh bond cleavage/re-formation catalyzed by water, resulting in the formation of the mono­(μ-oxo)-bridged rac-helicate, which reverted back to the original bis­(μ-hydroxo)-bridged meso-helicate upon hydration in aqueous CD3CN. These reversible transformations between the meso- and rac-helicates were also promoted in the presence of a catalytic amount of an acid, which remarkably accelerated the reactions at lower temperature. Interestingly, in anhydrous CD3CN, the bis­(μ-hydroxo)-bridged meso-helicate was further slowly converted to a different helicate, while its meso-helicate framework was maintained, namely the mono­(μ-oxo)-bridged meso-helicate, through dehydration upon heating and its meso to meso transformation was significantly accelerated in the presence of cryptand[2.2.1], which contributes to removing Na+ ions coordinated to the helicate. Upon cooling, the backward meso to meso transformation took place via hydration. Hence, three different, discrete double-stranded chiral rac- and achiral meso-titanium­(IV) helicates linked by a mono­(μ-oxo) or a bis­(μ-hydroxo) bridge were successfully generated in a controllable manner by a change in the water content of the reaction media.

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SynopsisCarbon fibers having good mechanical properties were produced from syndiotactic 1,Zpolybutadiene (s-PB). Melt-spun s-PB fibers were made infusible by oxidation, irradiation, or treatments with Lewis acids, protonic acids, or peroxides. The infusibilized fibers were dehydrogenated with oxygen, chloranil, or sulfur and then carbonized. The preparative method by the AlBr,-sulfur-heat treatment process gave carbon fibers with good mechanical strength in a high yield. A filaments bundle was immersed in a benzene solution of AlBr, (2g/100mL) a t 42°C for 78 min under tension, washed with methanol, and then immersed in molten sulfur at 275°C for 14 min. After the adhering sulfur was purged with nitrogen at 290°C for 7 min, the bundle was heated up to a temperature of 700-3000°C under tension in a flow of nitrogen or argon for a few minutes. Carbon fibers heated to 1400°C were obtained with the tensile strength of 16.6 t/cm2 and the modulus of 1420 t/cm2 in a carbon yield of 82% and straingraphitized fibers at 3000°C with 20 t/cmz and 4010 t/cm2 in 70%.