MONODISPERSE MICROBEADS OF HYPERCROSSLINKED POLYSTYRENE
2065
medium of the same composition. The mixture is
EXPERIMENTAL
slowly stirred until, due to diffusion through the aque-
ous phase, the starting suspension and emulsion forms
a single uniform system in which the disperse phase is
a solution of linear polystyrene in the mixture of added
comonomers and porogene. Subsequent polymeriza-
tion of the monomers at high temperatures produces
monodisperse crosslinked microspheric particles.
Finally, the removal of stabilizers from the surface and
the extraction of linear polystyrene yield macroporous
copolymer particles. Although this method allows us
to obtain desirable microspheric sorbent beads with a
rather narrow size distribution, it is very time consum-
ing and labor intensive with low productivity and
reproducibility.
Reagents and Materials
,2-Dichloroethane was dried by refluxing over
phosphoric anhydride for two hours and distilled over
a fresh portion of drying agent. A 65% solution of divi-
nylbenzene (Merck) in styrene was purified from
inhibitors by washing with 10% KOH and water until a
neutral reaction. The organic solution was then passed
through alumina.
1
HPLC-grade acetonitrile, reagent-grade methanol
(
LabScan), and food-grade carbon dioxide (Linde-
Gas Rus) were used in our chromatographic experi-
ments.
Synthesis of Chloromethyl Methyl Ether
Dispersion polymerization [9] is simpler single-
step method for synthesizing monodisperse micro-
spheres. A monomer, a radical polymerization initia-
tor, and a stabilizer of the future suspension of polymer
particles are dissolved in an organic solvent (e.g., ali-
phatic hydrocarbon). As polymerization proceeds, the reaction mass was cooled to −5°C and concentrated
resulting polymer chains precipitate as spherical parti- hydrochloric acid (120 mL) was added dropwise for
cles from the dispersion medium, which serves as their 1 h at this temperature. Concentrated sulfuric acid
A four-necked flask equipped with a stirrer, drop-
ping funnel, thermometer, and reflux condenser was
loaded with methanol (32 g, 1 mol) and pre-ground
paraform powder (30 g, 1 mol). The mixture was
stirred thoroughly and NaCl (30 g) was added. The
о
precipitating agent. Correct selection of the precipitat- (120 mL) was also added slowly at −5 C. Stirring and
ing medium, concentrations of components, and pro- cooling continued for an additional 5 h until the disso-
cess conditions allow us to obtain size-uniform poly- lution of paraform was complete. When the reaction
finished, the upper layer was separated and distilled to
collect the fraction boiling at 59–61°C. The yield of
ether was 60%. In conducting the procedure, we must
also remember that CMME (CAS 107-30-2) is a
class 3 hazard compound and irritates the respiratory
tract [11].
mer microspheres. At present, the convention is to dis-
tinguish between dispersion polymerization and
precipitation polymerization. Dispersion polymeriza-
tion is understood to mean the synthesis of linear
polymers in the presence of suspension stabilizers and,
as when preparing crosslinked polymer microbead
without using a stabilizer, it is referred to as precipita-
tion polymerization [10, 11]. This division is some-
what arbitrary and does not consider the mechanism
of particle formation (which is undoubtedly identical
in both cases), but the term “precipitation polymer-
ization” is now commonly accepted in the literature.
Synthesis of Styrene–Divinylbenzene (1%) Copolymer
Microbeads
PES-5 polydiethylsiloxane liquid (63 mL) and
n-octane (63 mL) were mixed in a flask. A mixture of
styrene (25 mL), DVB (0.5 mL), and azobisisobutyro-
nitrile (AIBN) (0.46 g) were added to this solution.
The reaction mixture was stirred until a clear solution
was obtained; it was then heated at 70°C for 4 h. At the
end of this period, the mixture was left at room tem-
perature for 20 h. The resulting beads were filtered off,
washed on a filter with hexane and ethanol, and
In this work, we present the results from a high-
throughput procedure for precipitation polymeriza-
tion that we developed for preparing monodisperse
microbeads of styrene-divinylbenzene (DVB) copoly-
mer. The copolymer beads were then additionally
crosslinked with 1, 1.5, 2, and 2.5 moles of chloro-
methyl methyl ether (CMME) up to degrees of cross-
linking of 200, 300, 400, and 500%, respectively. We
discuss some physicochemical aspects of the synthesis
of microspherical styrene–DVB copolymers, their
properties, and the properties of crosslinked sorbents
based on them. The chromatographic properties of an
HPLC column filled with crosslinked (300%) polysty-
rene microbead sorbents are tested using the example
(
if necessary) dried in air.
The synthesis of hypercrosslinked polymers was
described in detail in [12].
Polymer swelling by weight (K ) was determined as
wt
follows: Polymer swollen in toluene (or water) was
separated from the excess of solvent via filtration and
the beads were dried on a Petri dish until they started
to roll on a glassy surface and were quickly transferred
to three preweighed weighing cups. The polymer was
of separating the model mixture in the isocratic and weighed in the swollen state and dried at 100°C until a
gradient modes, and under the conditions of super- constant weight was achieved. The swelling was calcu-
critical fluid chromatography.
lated as the amount of solvent absorbed per one gram
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 89 No. 11 2015