TABLE OF CONTENTS Let us note once again that, in dependence on temperature, amorphous polymer may exist in three physical states: glassy, rubbery and viscous flow. Methods of estimation of the glass transition temperature, T g, of polymers based on chemical structure of the repeat unit are discussed above. Estimation of not only glass transition temperature T g, but also temperature of transition into the viscous flow state T f, which determine the temperature range of the rubbery state, by the chemical structure of polymer is extremely desirable. Therewith, the value of T f is necessary for processing of polymers.
The position of T f in relation to T g of the polymer is closely linked with the molecular mass of the chain M.
An attempt to estimate T f was made in ref. [96]. It is based on application of an expression that sets the dependence of zero (Newtonian) shear viscosity ? 0 on the molecular mass M [177]:
| (V.1) |  |
where 
( b is the segment length; N 0 is the number of segments composing the present macromolecule; ? is the friction coefficient of the segment, including external and internal friction of the initial macromolecule; k B is the Boltzmann constant); M e is the mass of the macromolecule, starting from which entanglements of chains affect significantly the melt viscosity; R is...
