Yu. V. Zelenev

Manifestation of Molecular Mobility of Polymers of Different Classes over a Wide Temperature Range

One of the most important problems tackled by modern polymer science is establishing the relationship of the macroscopic physical properties of polymers in bulk with their structure and the nature of thermal flow of the corresponding kinetic units. Understanding the molecular mechanism of manifestation of particular macroscopic properties of polymers means the possibility of influencing them in the necessary direction, i.e. learning to create polymeric materials with specified properties. Most information for solving the problem formulated can be obtained by a complex study of the molecular relaxation processes in polymers by different physical methods of relaxation spectrometry. The mechanical losses at T > T 0 , just like the modulus, depend greatly on the molecular weight. The magnitude of the minimum of mechanical losses at T > T 0 decreases with increase in molecular weight. The minimum of mechanical losses is observed close to the centre of the high elasticity plateau, where there is an inflection on the temperature dependence of the modulus. It was established that the mechanical losses are a function of the number-average and weight-average molecular weight. It was also established that the breadth of the minimum of losses increases with increase in polydispersity, i.e. with increase in the ratio of the weightaverage and number-average molecular weight. The values of moduli G ′ and G′′ in the high elasticity (rubbery) region do not depend on the molecular weight since the molecular weight between entanglements is constant for the given polymer (ref. 1). However, with increase in molecular weight, the plateau covers a wider range of frequencies. When T < T g , the molecular weight has only a very slight effect on the dynamic properties of the polymers. The most common types of polymer are those possessing a three-dimensional network. The most important characteristic of such polymers is their degree of crosslinking: