The effect of molecular weight distribution on the physical properties of polystyrene

Abstract

Mechanical properties and melt viscosity have been measured on anionc polystyrene of narrow molecular weight distribution and thermal polystyrene of broad molecular weight distribution in an attempt to study the effect of molecular weight distribution. Tensile strength and elongation were found to depend upon some molecular weight between weight‐average and number‐average and not on number‐average molecular weight alone, as previously reported, while tensile impact strength depends upon weight‐average molecular weight, and modulus is essentially independent of molecular weight or molecular weight distribution. There is indication that high shear melt viscosity does not depend upon weight‐average molecular weight as does zero shear viscosity due to the effect of molecular weight distribution on non‐Newtonian flow characteristics. Complete analysis indicates little chance for a narrowing of the polymer distribution to permit an increased ease of fabrication without detrimental effects on the mechanical properties.