The effect of molecular properties on the mechanical behaviour of PMMA—IV. The role of chain entanglements in fracture processes

Abstract

The fracture-toughness—entanglement correlation was shown to be a more fundamental concept than the fracture-toughness—glass transition temperature or the fracture-toughness—solubility-parameter correlations in predicting the effect of molecular weight, molecular weight distribution, stereoregularity and temperature on the fracture behaviour of poly(methyl methacrylate) (PMMA). Morphological study of the fracture surface by scanning electron microscopy (SEM) of high molecular weight PMMA in good and bad solvents and blends of isotactic PMMA and low molecular weight atactic PMMA supports the relationship between molecular entanglements and fracture behaviour. The entanglement network at the crack tip determines whether failure occurs in solvents by rapid stress-cracking or stress-crazing with long-craze growth.