LOW DIELECTRIC LOSS POLYETHYLENE POLYMERIZED WITH CHROMOCENE CATALYST

We studied the polymerization of ethylene monomers with chromocene cat alyst to produce polyethylene with low dielectric loss in the microwav e region. Chromocene (bis-cyclopentadienyl chromium) is very active fo r a long period during ethylene polymerization, and it also has a very low dipole moment because of its symmetrical molecular structure. Pol yethylene polymerized by using chromocene has a low dielectric loss in the 500 MHz region caused by gamma relaxation. We were able to calcul ate the loss in this wavelength region from a summation of each indivi dual contribution. The contributors included catalyst residue, and pol ar groups, i.e., methyl groups and double bonds such as vinyl, interna l trans-vinylene, and vinylidene groups at a certain crystallinity. In order to make low dielectric loss polyethylene with a chromocene cata lyst, we first tried to improve both the process of ethylene polymeriz ation with a chromocene catalyst and the dielectric loss (tan delta) o f polyethylene at 500 MHz. We measured the number of polar groups and the residual catalyst in polyethylene with the IR method. Our results revealed that both the hydrogenation reaction that occurs during ethyl ene polymerization with the chromocene catalyst and the crystallizatio n of polyethylene after polymerization were very effective in reducing the dielectric loss of polyethylene. (C) 1998 John Wiley & Sons, Inc.