A theoretical analysis has been performed for experimental data on internal friction spectra and temperature–frequency dependences obtained by the method of free damped torsional oscillations for diverse liquid hardeners (TETA, PEPA, and MTHPA) of epoxy oligomers. The main phenomenological model representations have been considered and employed to analyze various physicomechanical and physicochemical characteristics of local dissipative processes, which may have different mechanisms of internal friction (hysteresis-, phase-, and relaxation-type).

A study was conducted on the internal friction spectra and temperature dependencies of the frequency of free damped oscillatory processes excited in the investigated samples of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) over a temperature range from −150 °C to +150 °C. It was found that the internal friction spectra exhibit several local dissipative processes of varying intensity, which manifest in different temperature intervals. The structure of the internal friction spectra and the peaks of dissipative losses are complex, as evidenced by the occurrence of sharp, locally temperature-dependent jumps in the intensity of dissipative losses observed throughout the entire temperature range. A theoretical analysis was performed to explore the relationship between the anomalous change in the frequency of the oscillatory process and the defect in the shear modulus, as well as the mechanisms of internal friction for the most intense dissipative loss processes identified in the internal friction spectra. A significant difference was revealed in the structure of the internal friction spectra of LDPE and HDPE in the temperature range of −50 °C to +50 °C. A comparison of the LDPE and HDPE samples was conducted based on changes in their strength characteristics, taking into account the locally temperature-dependent changes in the shear modulus caused by local dissipative losses observed in the internal friction spectra.

The study of spectra of internal friction $\lambda =f\left(T\right)$ and temperature dependencies of frequency of freely damped $\nu =f\left(T\right)$ oscillatory process excited in investigated samples of polyethylene with different degree of crystallinity in the temperature range from −150 ${}^{°}$C to +150 ${}^{°}$C. It is established that four local dissipative processes of different intensity shown in different temperature intervals are observed on the spectra $\lambda =f\left(T\right)$. These are $\mu$, $\beta$, $\alpha$, ${\beta }_k$ processes. The theoretical analysis of the relationship between the anomalous changes of the vibrational process frequency $\nu =f\left(T\right)$ and the shift modulus defect $\Delta G=f\left(T\right)$ and the internal friction mechanisms for each of the dissipative loss processes detected on the spectrum $\lambda =f\left(T\right)$ is carried out. The influence of supramolecular structures on local dissipative ${\beta }_k$ process in polyethylene is estimated.

The spectra of internal friction and temperature dependencies of the frequency of a free-damped oscillation process excited in the specimens of an amorphous–crystalline copolymer of polyoxymethylene with the co-monomer trioxane (POM-C) with a degree of crystallinity ~60% in the temperature range from −150 °C to +170 °C has been studied. It has been established that the spectra of internal friction show five local dissipative processes of varying intensity, manifested in different temperature ranges of the spectrum. An anomalous decrease in the frequency of the oscillatory process was detected in the temperature ranges where the most intense dissipative losses appear on the spectrum of internal friction. Based on phenomenological model representations of a standard linear solid, the physical–mechanical (shear modulus defect, temperature position of local regions of inelasticity) and physical–chemical (activation energy, discrete relaxation time, intensities of detected dissipative processes) characteristics of each local dissipative process were calculated. It was found that the intensities of dissipative processes remain virtually unchanged for both annealed and non-annealed samples. The maximum variation in the shear modulus defect is 0.06%. Additionally, according to computational data, small changes are also characteristic of the following parameters: the activation energy varies from 0.5 to 1.4 kJ/mol and the relaxation time changes from 0.002 to 0.007 s, depending on the presence or absence of annealing. As a result of annealing, there is a significant increase in the relaxation microinheterogenity of the polymer system across the entire temperature range (250% for the low-temperature region and 115% for the high-temperature region).

The effect of electron irradiation (doses up to 53 kGy) on the relaxation properties and segmental mobility in polyvinyl alcohol molecules has been studied using relaxation spectrometry. It has been shown that radiolysis leads to the formation of radicals that do not cause crosslinking of polymer chains. Irradiation with electrons causes a linear increase in the relaxation microheterogeneity of the alpha-process in the internal friction spectrum; this change manifests itself in broadening of the corresponding loss peak.

The study of local dissipative processes by the method of free-damped torsional oscillations excited in polyvinyl alcohol (PVA) showed the presence of three loss peaks in the internal friction spectrum in different temperature ranges of this spectrum [1].