Fracture processes in polymeric materials. V. Dependence of the ultimate properties of poly(methyl methacrylate) on molecular weight

The influence of molecular weight on the fracture surface energy, Young's modulus, tensile strength, and inherent flaw size in poly(methyl methacrylate) has been determined. In common with other mechanical properties, the dependence of the fracture surface energy on molecular weight can be represented by γ = A – ( B / M ), where M is the molecular weight, and A and B are arbitrary constants. By extrapolation, the upper limiting value is 1.55 × 10 5 ergs/cm. 2 , while the surface energy, and hence the tensile strength, should become zero for a polymer of molecular weight 25,000. This value is in good agreement with that found directly from brittle strength measurements.