ELASTIC MODULUS OF AN AMORPHOUS GLASSY POLYMER

Amorphous polymers in their glassy state have elastic moduli a few times 1010 dyne cm-2, and these low values have been attributed to the weak intermolecular van der Waals polarization forces holding the material together. It is suggested that because of the imperfect chain packing in amorphous polymers, intermolecular forces, which fall off rapidly with increasing molecular separation, may not be sufficiently large to account for the observed moduli. An alternative explanation for the stiffness of these materials is that elongation of the randomly kinked chains making up the polymer can take place by rotation about selected carbon-carbon bonds in the chain backbone, and it is this rotation against intramolecular steric hindrance forces that controls the modulus. This mechanism is estimated to give rise to a modulus of approximately 6 × 1010 dyne cm-2. © 1968.