Chapter V: Temperature of Transition into the Viscous Flow State for Amorphous Polymers

V.1 Estimation of Temperature of Transition into the Viscous Flow State of Polymers

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...