The role of molecular weight and temperature on the elastic and viscoelastic properties of a glassy thermoplastic polyimide

• Published in: International journal of fatigue Vol. 24; no. 2; pp. 185 - 195
• Main Authors: Nicholson, Lee M., Whitley, Karen S., Gates, Thomas S.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01.04.2002; Elsevier Science
• Subjects: Applied sciences; Creep-compliance; Exact sciences and technology; Mechanical properties; Modulus; Molecular weight; Organic polymers; Physical ageing; Physicochemistry of polymers; Polyimides; Properties and characterization; Strength; Creep-compliance; Physical ageing; Modulus; Molecular weight; Strength; Polyimides; Viscoelasticity; Polyimide; Creep; Glassy polymer; Aromatic polymer; Mechanical properties; Temperature effect; Tensile property; Experimental study; Structure relaxation; Molecular weight property relation
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/S0142-1123(01)00072-X

Mechanical testing of the elastic and viscoelastic response of an advanced thermoplastic polyimide (LaRC™-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The notched tensile strength was shown to be a strong function of both molecular weight and temperature, whereas stiffness was only a strong function of temperature. A critical molecular weight was observed at a weight-average molecular weight of M ̄ w ∼22 000 g/mol below which the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Low molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure. Furthermore, low molecular weight materials have increased creep compliance and creep compliance rate and are more sensitive to temperature than the high molecular weight materials. At long timescales (>1100 h) physical ageing serves to significantly decrease the creep compliance and creep rate of all the materials tested. Low molecular weight materials are less influenced by the effects of physical ageing.