Dielectric relaxations in amorphous polymers with complex chain architectures
By combining thermostimulated current and dynamic dielectric spectroscopies, the dielectric properties characteristic of the molecular mobility can be described over a very broad frequency range. The study of dielectric relaxations of phosphorus-containing dendrimers in the sub-glass transition region, and of poly(n-alkyl methacrylates) at and above the glass transition region allows us to gain insight into the molecular dynamics of complex architecture systems. From these sets of data we make an attempt to propose a structural interpretation of molecular mobility through the glass transition.
Dynamic shear modulus in the splitting region of poly(alkyl methacrylates)
A systematic study of the dynamic shear modulusG*=G′+G″ in three poly(alkyl methacrylates) (PEMA, PnPMA, PnBMA) at frequencies between 0.001 and 500 rad/s is presented. As the αβ splitting frequencies ωs are low, aging effects can be observed in the splitting region. There is a systematic shift of the splitting frequency ωs to lower values with increasing length of the alkyl side group. In PnBMA a separate shear α appearance is observed about two frequency decades below the local mode β. This is discussed in terms of the concept of minimal cooperativity. Aging effects are: Shift of the maximum loss frequency ωα to lower values, peak sharpening of the α relaxation, and intensity changes of α and β. These effects are discussed in terms of the sequential aging concept. Aging leads to a pronounced bending of the α traces upwards from the equilibrium line in the Arrhenius diagram. These non-equilibrium phenomena are promoted by the small slope mα=d(log ωα)/dT of the α trace in the splitting region.
Evaluation method of temperature-dependent relaxation behavior of polymers
An evaluation technique is proposed which decomposes the temperature-dependent relaxaation function of a polymer into the amounts of the overlapping relaxation functions of the individual mechanisms. Each mechanism is described by a seven-parameter model function that is derived from the model function of Havriliak and Negami using temperature-dependent parameters. The evaluation technique is adapted from a method well tried in the frequency domain. For torsional pendulum measurements on a blend of polyamide 6 and ethylenevinyl acetate copolymer the power of the evaluation method to clear up the morphology is shown