Russian Chemical Bulletin, International Edition, Vol. 52, No. 3, pp. 771—772, March, 2003
771
Gelꢀfree process of synthesis of poly(vinyl alcohol)
ꢀ
V. V. Boiko, A. A. Kuznetsov, G. K. Semenova, and A. N. Ozerin
N. S. Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Sciences,
70 ul. Profsouyznaya, 117393 Moscow, Russian Federation.
Fax: +7 (095) 420 2229. Eꢀmail: vboi@ispm.ru
PVA (%)
0.8
It is known that the synthesis of poly(vinyl alcohol)
(PV) by alcoholysis of poly(vinyl acetate) (PVA) in MeOH
in the presence of alkaline catalysts is accompanied by a
sharp change in the phase state of the system resulting in
gel formation.1,2 A consequence of this very undesirable
process is a decrease in the reaction rate and the limiting
degree of conversion. It has been considered until reꢀ
cently that the necessary conditions for a high conversion
of alcoholysis to attain are the use of anhydrous alcohol
(total water content in the system <0.7 wt.%)1 and an
elevated temperature (40—60 °С) of the last step of the
reaction. The process of PV synthesis by alkaline hydrolyꢀ
sis of PVA in water is also known.3 It occurs from the very
beginning under heterogeneous conditions and is also acꢀ
companied by gel formation. The duration of the process
is several hours. An excess of alkali (>1.1 moles per mole
of elementary units) is required to achieve a high degree
of conversion.
We established that, when waterꢀalcoholic mixtures
are used as media, the polymerꢀanalogous transformation
of PVA into PV in the presence of NaOH occurs with a
high rate up to a high degree of conversion even at 20 °С
without gel formation. In a typical experiment in a reactor
with a stirrer, the time of synthesis was 30 min. The initial
PVA was used as a 10% solution in a waterꢀalcoholic
mixture, and MeОН, EtOH, PrOH, or PriOH served as
alcohols. The alcohol/water ratio was varied from 40/60
to 90/10 wt.%, and the consumption of alkali (NaOH)
ranged from 0.3 to 1 mole per mole of elementary units of
vinyl acetate (VA). For the EtOH/H2O (40 : 60 wt.%)
system, the consumption of alkali corresponding to the
achievement of 99.5% and 45.0% conversion was 0.5 and
0.3 moles per mole of elementary units, respectively. It
follows from these data that in waterꢀalcoholic media the
alkaline hydrolysis of PVA occurs in addition to alcoholyꢀ
sis, both reactions making comparable contributions to
the total conversion. Evidently, the change in the kinetic
parameters of the process is caused by a change in the
phase state of the system.
1
2
0.25
A, B
0.6
0.50
M
B
0.4
0.75
0.2
A
H2O (%)
N
0.25
0.50
0.75 EtOH (%)
Fig. 1. Phase diagram of the PVA—EtOH—water system with
experimental points corresponding to the solubility (1) and inꢀ
solubility (2) zones. Points А and В are the beginning of the
reaction route for saponification in a medium of anhydrous
alcohol (A) and in a waterꢀalcoholic medium (B).
mixtures (Fig. 2). The phase evolution of the reaction
system with an increase in the conversion of saponificaꢀ
tion can be monitored by the transition of the binodal
from the position NM (see Fig. 1) to the position N´M´
(see Fig. 2). The binodal position was determined by the
method of turbidity points. The route of PVA alcoholysis
Copolymer (%)
1
0.8
2
0.25
A´, B´
0.6
0.50
0.4
0.75
0.2
B´
A´
H2O (%)
M´
0.75 EtOH (%)
0.25
0.50
N´
Fig. 2. Phase diagram for the copolymer containing 50% reꢀ
sidual acetate groups. Experimental points correspond to the
solubility (1) and insolubility (2) zones. Points А´ and В´ are the
points of the reaction route for the 50% conversion of saponifiꢀ
cation in a medium of anhydrous alcohol (А´) and in a waterꢀ
alcoholic medium (В´).
In order to confirm this assumption, we studied the
triple phase diagrams for the initial PVA (Fig. 1) and
copolymer containing 50% acetate groups in H2O—EtOH
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 735—736, March, 2003.
1066ꢀ5285/03/5203ꢀ771 $25.00 © 2003 Plenum Publishing Corporation