Linear and non-linear viscoelastic behavior of poly(methyl methacrylate) in the hard region

The relaxation behavior of poly(methyl methacrylate) in the hard region is caused by hindered rotations of the methoxycarbonyl side groups of the molecules. Measurements of the Young's modulus and the shear modulus at different frequencies, temperatures and strains lead to the following conclusions: each moving side group is surrounded by the elastic matrix of mean chains, The elasticity of this matrix depends on volume and temperature. Also the activation energy of the moving side group depends on volume and temperature, because the activation energy is the sum of an intramolecular and an intermolecular component. Due to the statistical entanglement of the molecules, the intermolecular contribution to the activation energy has a statistical distribution depending on volume. The reaction rate theory is of value for interpreting the viscoelastic behavior in the linear and non-linear range if several considerations are followed.