SynopsisSome results on the melt rheology of hydrogenated polybutadiene (HPB) with narrow-molecular-weight distribution are reported and compared with the corresponding properties of the precursor polybutadienes (PBD) and fractions of linear polyethylene (PE). In linear samples the dynamic moduli obeyed frequency-temperature superposition. The relationship between melt viscosity and intrinsic viscosity at 190°C for HPB was indistinguishable from that for PE, but their flow activation energies were slightly different (E, = 7.2 kcal for HPB and 6.4 kcal for PE). Like PE, but unlike the PBD precursors, the dynamic storage modulus at low frequencies was anomalous. Otherwise, the dynamic moduli of HPB and its PBD precursor were essentially superposable. Plateau moduli from different samples were somewhat variable around an average of GR = 2.31 X lo7 dyn/cm2. The dynamic moduli for the HPB stars, unlike their PBD precursors, did not obey temperature-frequency superposition. At high frequencies the temperature coefficient approached that for linear HPB, but it increased with decreasing frequency, reaching limiting values which depended on the arm length. The flow activation energy ranged from 9 kcal to more than 15 kcal as arm length increased.

SynopsisThree methods for hydrogenating anionically prepared polybutadiene (containing about 8% vinyl double bonds) were investigated: homogeneous catalysis (alkylated transition metal salts), heterogeneous catalysis (nickel on kieselguhr; paladium on calcium carbonate), and stoichiometric reaction with in situ generated diimide. The products were characterized by intrinsic viscosity, gel permeation chromatography, infrared spectroscopy, and melt viscosity. Only the heterogeneous catalysts were found to yield completely hydrogenated products without incorporation of foreign groups and without significant change in the large-scale molecular structure of the chain. The 195OC melt viscosity of linear polybutadiene hydrogenated with heterogeneous catalysts is virtually identical with that of linear polyethylene with the same intrinsic viscosity in trichlorobenzene at 135°C. The solid state properties of hydrogenated polyhutadiene, containing about 20 ethyl branches/1000 main chain atoms, closely resemble those of commercial branched polyethylene.

SynopsisSome results are reported on the linear viscoelastic properties of polybutadienes with narrowmolecular-weight distributions. The zero shear viscosity 70 varies as M3.4 in the linear samples, and viscosity enhancement is found in star-branched samples with long arms, in good agreement with results reported earlier by Kraus and Gruver. The temperature coefficient of viscosity appears to he slightly larger in stars when the arms become long. The steady state recoverable compliance J," is 2.1 X cm2/dyn in linear samples of high molecular weight, but it increases to values as much as 10 times larger in the stars. The plateau modulus Ga, obtained from a composite curve for the linear samples, is 1.32 X lo7 dyn/cm2. The terminal relaxation spectrum of the stars is too broad to allow an evaluation of plateau modulus.