A new type of insulating polymer, syndiotactic polypropylene prepared by metallocene catalyst has been found to exhibit much superior electrical, thermal and mechanical properties compared with those of conventional isotactic polypropylene, atactic polypropylene and polyethylene. These excellent characteristics of syndiotactic polypropylene are found to originate from lower crystallinity, much smaller spherulites, different crystal lattice and less residual catalysts than in isotactic polypropylene. To apply syndiotactic polypropylene to practical cable insulation, low temperature brittleness and thermal durability have been improved by blending and 600V and 22kV class cables have been successfully manufactured. With the electrical tests, these cables have been confirmed to exhibit excellent characteristics compared with conventional cross-linked polyethylene cables. It should also be mentioned that syndiotactic polypropylene is also suitable for recycle uses because it is not cross-linked.
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