Stereochemistry of poly(1,3-cyclohexadienes). NMR investigation of effects due to the solvent medium and to the mechanism of polymerization

Abstract

The 13C NMR and 1H NMR spectra of poly(l,3-cyclohexadiene) (PCHD) were analyzed. Anionically polymerized samples, cationically polymerized samples, and samples polymerized with a Ziegler-Natta catalyst were investigated. The NMR and 13C NMR spectra were taken at 270 and 67.88 MHz, respectively. The resolution of the former spectra was incomplete and they were deconvoluted by computer simulation. Relative intensities of the computer-resolved 1H NMR peaks were used in the calculation of the isomeric composition of the investigated PCHD's. 1H NMR results were confirmed qualitatively by 13C NMR results. 3,3'-Bicyclohex-l-enyl (BCH) was used as a model compound for the verification of the proposed assignment of the experimentally observed chemical shifts. The effect of solvents on the microstructure of the anionically polymerized 1,3-cyclohexadiene has been found to be essentially analogous to that observed for the acyclic dienes. Significant differences were, however, detected. For example, even in polar solvents the fraction of 1,2 isomers did not exceed 50%. Apparently, steric hindrance precludes the formation of long sequences of 1,2 units. The formation of intermittent 1,2 and 1,4 sequences is feasible and their fraction increases with increasing temperature. The anionic polymerization of 1,3-cyclohexadiene in hexane and in bulk yields the 1,4 isomer in a predominantly cis-type pianomeric conformation. The stereoselectivity of the cationic and the Ziegler-Natta systems is lower than that of the anionic ones.

Synthesis and Characterization of Star Copolymers Consisting of Fullerene and Conjugated Polyphenylene: 6-star-C60[styrene−poly(1,4-phenylene)-block-polystyrene] and 6-star-C60[polystyrene-block-poly(1,4-phenylene)]

“…90%). 8,11,40,41 The polymerization is however relatively slow, taking several days to reach elevated molecular weights (ca. 10 000), 16 and is subject to a high degree of secondary and chain termination reactions.…”

“…6 The most convenient route to PPP is the dehydrogenation of poly(1,3-cyclohexadiene) (PCHD) which is tractable. [8][9][10][11][12] PCHD is at present best synthesized via "living" anionic polymerization. This route has readily permitted syntheses of AB and ABA type copolymers of PCHD and polystyrene (PS).…”

Salt‐water recycling for brine production at road‐salt‐storage facilities

“…The dienic precursors analyzed by 1 H NMR spectroscopy (Bruker‐AC 200) in CDCl 3 at 30 °C were found to have the following microstructures: PBd, 8 wt % 1,2 and 92 wt % 1,4, and PCHD, 12 wt % 1,2 and 88 wt % 1,4. For PCHD, the 1,2/1,4 ratios were determined from the relative areas of protons adjacent to the double bond α position (1.85–2.35 ppm) and those in the β position (1.25–1.85 ppm) 5, 9, 22. Each 1,2‐unit has three α protons and three β protons, whereas a 1,4‐unit has two α protons and four β protons.…”

“…Improved thermal and chemical stability, as well as mechanical strength, has been found for these polymers 13–18. PCHD can be dehydrogenated into polyphenylene,19–21 a highly conductive polymer 22. It can be transformed into polycyclohexylene (PCHE) either by homogeneous hydrogenation with diimide23 or by heterogeneous catalytic hydrogenation with Pd/BaSO 4 or Pd/CaCO 3 13.…”

Anionic Polymerization of Cyclohexa‐1,3‐diene in Cyclohexane with High Stereoregularity and the Formation of Crystalline Poly(cyclohexa‐1,3‐diene)

“…Although the polymerization of cyclohexa‐1,3‐diene (CHD) can be carried out using radical, cationic, anionic, and transition metal systems, the best results with respect to conversion rate and molecular weight were obtained using organolithium compounds as initiators 1. The solvent medium and the presence of polar additives strongly influence the microstructure of anionically prepared poly(cyclohexa‐1,3‐diene) (PCHD) 2. In hydrocarbon solvents, 1,4‐addition (> 90%) predominated while in polar solvents, such as tetrahydrofuran (THF), a mixture of 1,2‐ (39%) and 1,4‐ (61%) addition was obtained.…”