Accession Number:

ADA230221

Title:

Microphase-Separation Interpretation of the Covariation of Several Polyurethane Dielectric Properties

Descriptive Note:

Corporate Author:

AEROSPACE CORP EL SEGUNDO CA LAB OPERATIONS

Personal Author(s):

Report Date:

1990-09-28

Pagination or Media Count:

26.0

Abstract:

Electronic power supplies, cables and other equipment depend upon the breakdown-free separation of charged conductors. This often requires the use of polymeric encapsulants or extruded dielectrics, whose thermal aging behavior is a concern. One high-voltage encapsulation is the polyurethane, Uralane 5853. It is composed of chain molecules based on a polybutadiene, existing in a long, flexible subchain soft segments, and b methylene diisocyanate, existing in a short, rigid subchain hard segments linking the flexible subchains. The hard segments in different chains tend to form hydrogen bonds and to phase separate. This work demonstrates the relation of Uralanes dielectric breakdown strength to its permittivity 50 Hz to 10 kHz and to its dc conductivity, thereby illustrating an analytical technique for use in the formulation and evaluation of new polyurethanes. It was found that the partially reversible reduction in paracrystalline domain size correlated with a decrease in dielectric breakdown strength during thermal aging. All other things being equal, increased phase separation leads to diminished leakage current through the dielectric, with fewer energetic electrons available to possibly initiate failure during electrical aging. Testing is in progress on a new series of polyurethanes in order to ascertain the optimum hard-segment composition for thermal-aging voltage stability.

Subject Categories:

  • Electrical and Electronic Equipment
  • Electricity and Magnetism

Distribution Statement:

APPROVED FOR PUBLIC RELEASE