Molecular weight dependence of mechanical properties of poly(p,p′‐oxydiphenylene pyromellitimide) films

The mechanical properties, i.e., Young's modulus, elongation, and tensile stress, were determined as functions of the molecular weight for films of poly(oxydi‐p‐phenylene pyromellitimide) prepared by thermal cyclization of the precursor poly(amic acid). The molecular weights of the samples were controlled by the monomer stoichiometry employed for the solution condensation of pyromellitic dianhydride and p,p′‐oxydianiline. Weight‐average molecular weights were determined by light scattering of the precursor poly(amic acid) as well as the fully cyclized polyimide. The elongation‐at‐break is most sensitive to the molecular weight, undergoing a rapid increase at Mw ⋍ 8000 and reaching a limiting value of about 60% for Mw > 20,000. Copyright © 1987 John Wiley & Sons, Inc.