1070-4272/02/7512-1993 $27.00 C 2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 12, 2002, pp. 1993!1998. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 12, 2002,
Original Russian Text Copyright + 2002 by Men’shikova, Evseeva, Chekina, Peretolchin, Skurkis, Ivanchev.
AND POLYMERIC MATERIALS
Synthesis of Monodisperse Polymethyl Methacrylate Particles
in Buffer Solutions under the Action
of Carboxyl-Containing Initiator
A. Yu. Men’shikova, T. G. Evseeva, N. A. Chekina,
M. V. Peretolchin, Yu. O. Skurkis, and S. S. Ivanchev
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received March 29, 2002
Abstract-Influence exerted by salts with buffering action and by the initial pH of the reaction mixture on the
polymerization kinetics, viscosity-average molecular weight, and amount and degree of surface carboxylation
of polymethyl methacrylate particles formed in the course of emulsifier-free emulsion polymerization of
methyl methacrylate initiated by 4,4`-azobis(4-cyanoisovaleric acid) was studied.
Synthesis of monodisperse polymethyl methacry-
late (PMMA) particles with surface carboxy groups
by emulsion polymerization of methyl methacrylate
(MMA) with a carboxyl-containing azo initiator is
complicated by partial hydrolysis of the monomer
to methacrylic acid (MAA), which is especially pro-
nounced at high initial pH of the reaction mixture .
In this case, MAA formed in the course of the syn-
thesis copolymerizes with MMA, producing water-
soluble oligomeric products and considerably reduc-
ing the size of the resulting particles. In this context,
the method for directed control of the size of polymer
particles by varying the initial pH of the reaction
mixture, which provides good results in polymeriza-
tion of styrene [2, 3], needs further modification in
the case of MMA. The essence of the method indi-
cated is that, in the course of polymerization, terminal
carboxy groups of the initiator residues move toward
the interface during formation of polymer-monomeric
particles (PMPs). The surface charge formed as a re-
sult of ionization of these groups stabilizes PMPs
through electrostatic repulsion.
Therefore, the degree of ionization of the initiator
carboxy groups and carboxyl-containing styrene poly-
merization products strongly affects the size of the re-
sulting particles, which allows its directed control by
varying the initial pH of the reaction mixture. However,
in the course of MMA polymerization started in an al-
kaline medium, the formation of MAA shifts pH to
lower values, thus reducing the surface charge of PMPs
and impairing the stability of the polymer dispersion.
Furthermore, insertion of units of a carboxyl-contain-
ing comonomer into the oligomeric chains reduces
their surface activity, thus changing the PMP forma-
tion conditions. To overcome these difficulties and to
reveal factors controlling characteristics of the result-
ing PMMA particles, we studied the effect of salts,
capable of stabilizing pH in weakly acidic or weakly
alkaline medium, on the course of synthesis.
Methyl methacrylate, isoamyl alcohol, and DMF
were purified by distillation by the standard proce-
dures. 4,4`-azobis(4-cyanoisovaleric acid) (CVA) was
purified and characterized as in . Suberic acid
COOH ([Ferak]), NaOH, HCl, NaCl,
Fig. 1. Titration curves of the reaction mixture at 293 K.
(NaOH) Amount of alkali consumed for titration. Salt
concentration (M): (1) 0.02 M NaCl, (2) 0.01 M Na
(3) 0.02 M Na
, and (4) 0.02 M KH
. Nos. 137
correspond to run nos. in the table.