1070-4272/02/7506-1032 $27.00 C 2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 6, 2002, pp. 1032!1033. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 6, 2002,
Original Russian Text Copyright + 2002 by Kudyshkin, Abdurakhmanova, Ruban, Voropaeva, Rashidova.
Synthesis of Polyvinylpyrrolidone
under Secondary Inhibition Conditions
V. O. Kudyshkin, T. R. Abdurakhmanova, I. N. Ruban,
N. L. Voropaeva, and S. Sh. Rashidova
Institute of Polymer Chemistry and Physics, Academy of Sciences of Uzbekistan Republic, Tashkent, Uzbekistan
Received February 7, 2002
Abstract-A new approach to controlling the molecular weight of polyvinylpyrrolidone in radical polymeriza-
tion is considered. When the reaction is performed in the presence of a stable nitroxyl radical, 2,2,6,6-tetra-
methylpiperidyl-1-oxyl, the effect of secondary inhibition is manifested after the end of the induction period.
This effect can be used for preparing polymers with prescribed molecular weights.
The molecular weight M of polyvinyllactams, and
in particular, polyvinylpyrrolidone (PVP) in radical
polymerization can be controlled by weak inhibition
and chain-transfer reactions . Previous studies have
shown that the post-induction period in polymeriza-
tion of some vinyl monomers in the presence of stable
nitroxyl radicals is characterized by secondary inhi-
bition, which can occur by a catalytic or common
mechanism [2, 3]. Here we show that the post-induc-
tion inhibiting effect in radical polymerization can be
used for preparing PVP of desired molecular weight.
The reaction mixture consisting of the monomer,
initiator (AIBN), solvent (dioxane), and inhibitor
(2,2,6,6-tetramethylpiperidyl-1-oxyl, TEMPO) was
placed in glass ampules. The mixture was deaerated
by repeated freeze3pump3thaw cycles (residual pres-
sure 0.13 Pa). The synthesis was performed at 60oC.
The polymers were reprecipitated into diethyl ether.
The polymerization kinetics was studied dilatomet-
rically. The intrinsic viscosity of the polymers was
determined in water at 25oC. The experimental data
were processed in the Huggins3Kraemer coordinates.
For all the samples, the sum of the Huggins and
Kraemer constants K
; 0.5. The molec-
ular weights were calculated by the equation [h]=
3.1 0 10
The figure shows how the PVP yield varies in
the course of synthesis. Immediately after the end of
the induction period t
, a non-steady-state period is
observed in which the polymerization rate grows.
Then the system reaches a steady state, and VP poly-
merizes at a constant rate v
, which is lower than
in the absence of TEMPO (see figure, table). The
decreased polymerization rate is due, among other
things, to partial decomposition of the initiator during
the induction period. However, the fact that the prod-
(where [I] is the AIBN concentration by
the end of the induction period) decreases with in-
creasing TEMPO concentration in the initial mixture
(see table) shows that the decreased v
accounted for solely by the lower initiation rate. Ap-
parently, adducts formed by reaction of active radi-
cals with TEMPO can react with chain propagation
radicals, producing weak secondary inhibition after
the end of the induction period . This process
must affect the molecular weight of PVP. Indeed,
despite the fact that the reaction occurs under con-
PVP yield, A, vs. synthesis time t. [TEMPO] 0 10
(1)0,(2) 1.17, (3) 2.35, (4) 3.52, and (5) 4.71. Induction
period, min: (1)0,(2) 80, (3) 140, (4) 225, and (5) 355.