Influence of molecular weight and molecular weight distribution on mechanical properties of polymers

This work reviews the literature published over the last ten years on polymer mechanical properties as a function of molecular weight and molecular weight distribution, Thermal properties, stress‐strain properties, impact, fracture, fatigue, creep, stress relaxation and cracking and crazing are examined for a wide variety of homopolymers and a limited number of copolymers. In general, mechanical properties increase as the molecular weight increases. However, above some limiting molecular weight the mechanical property is usually unaffected. Although much work has been done to describe the effects of molecular weight on mechanical properties, little quantitative correlation exists. The available equations to predict such properties as cracking and crazing, Tg, Tm and tensile strength from molecular characteristics are discussed in detail. However, a more quantitative description incorporating a wider range of mechanical properties would be more useful. This would facilitate use of the vast amount of information available and enable it to be applied more readily to new polymer systems.