Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 1, pp. 153−155.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © K.V. Pochivalov, A.N. Vyalova, R.Yu. Golovanov, L.N. Mizerovskii, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85,
No. 1, pp. 160−162.
On the Procedure of Constructing Phase Diagrams
of Partially Crystalline Polymer–Liquid Systems
K. V. Pochivalov, A. N. Vyalova, R. Yu. Golovanov, and L. N. Mizerovskii
Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
Received July 21, 2011
Abstract—The procedure of constructing phase diagrams of partially crystalline polymer–liquid systems, which
is based on a difference in refraction indexes of a pure liquid and its solutions in partially crystalline and high-
elasticity polymer was proposed.
It was shown in [1–4] that phase equilibria in partially
crystalline polymer–liquid systems cannot be adequately
reﬂ ected by a diagram containing only one boundary
curve describing dependence of melting points of polymer
crystallites on the initial ratio of components of a binary
mixture and taken (by analogy to the systems of two
crystallizing low-molecular liquids) as a liquidus curve.
Such diagram (Fig. 1) should contain at least one more
boundary curve (line BD) reﬂ ecting conversion of the
initial two-phase polymer–liquid system into a single-
phase system: a solution of a liquid in amorphous ﬁ elds
of a partially crystalline polymer.
This is a phase line also in another sense. It is a right
binodal branch reﬂ ecting the extraction or osmotic equi-
librium in a partially crystalline polymer–liquid system
. However, this is the ﬁ rst sense, which is fundamen-
tally important for understanding the essence of processes
taking place in such system with a ﬁ xed composition and
Actually, let the binary mixture with a composition
corresponding to point k is heated up to the temperature
corresponding to point k
. In this case we shall meet two
characteristics: the temperature Т
of the full dissolution
of 0.4 weight fraction of liquid in amorphous ﬁ elds of
a polymer; the melting point Т
of the last crystallite in
the single-phase system of a polymer gel with grid nodes
in the form of crystallites.
Though line BD, which reﬂ ects the dependence of Т
on the initial binary mixture composition, can be success-
fully constructed by results of a sorption experiment with
excess liquid, it is methodologically important to have
a possibility of its constructing by the direct determination
of the temperature of conversion of a two-phase system
into a single-phase system. The procedure described
below allows us to do it.
The procedure is based on the difference of refraction
indexes of a swelling polymer and a liquid, which makes
it possible to ﬁ x the presence of this latter in the system
by the presence of its meniscus.
The difference in refraction indexes of coexisting
phases decreases during the experiment ﬁ rst of all due to
the conversion of a pure liquid into a solution of polymer
fractions in it, which do not participate in the formation
of crystallites. Therefore it is expedient to extract prelimi-
nary these fractions from the polymer at a temperature
close as much as possible to that corresponding to point
B in the phase diagram (Fig. 1).
Low-density polyethylene (LDPE) of 15083-020
grade (GOST 16377-77) with a melt index of 1.32 ±
0.2 g/10 min and a melting point of 111.2 ± 0.4°С used in
this work was extracted by chemically-pure grade toluene
at 64°С within 5 h.
The installation (Fig. 2) consisted of magnetic stirrer
1 and thick-walled glass 2 with teﬂ on cap 3 disposed on
the stirrer. The glass was ﬁ lled with a PMS-20 polymeth-
ylsiloxane liquid that allows using a KhK 4 thermocouple