Uniaxial Extension and Order Development in Flexible Chain Polymers

Abstract

It is well known that the highest elastic moduli reported for linear poly-mers are generally much smaller than their theoretical values. This has been shown particularly by Nakamae and coworkers [1]. For a range of poly-mers they have summarized their crystal moduli determined by x-ray dif-fraction as measured in the stiffest direction, parallel to the polymer chain axis. These values on crystals approximate the ultimate polymer moduli; they therefore may be compared with the much lower presently reported values for the conventional structure of these polymers (Fig. 1). This figure shows that most polymers, including those with rigid backbone chains, have tensile moduli far below those of their crystalline lattice in the chain direction. The exceptions are specially drawn ultrahigh molecular weight polyethylene (UHMW PE), which in PE parlance is generally considered to mean molecular weight above one million, and for isotactic polypropyl-ene that also has been drawn to tensile moduli that approach the value from theory.