Living-Free-Radical Emulsion Photopolymerization of Methyl Methacrylate by a Surface Active Iniferter (Suriniferter)

Article abstract of DOI:10.1021/ma034331i

A novel surface-active RAFT agent as a suriniferter, composed of the dithiobenzoyl main structure and a benzoic hydrophobic carboxylate hydrophilic moiety, was synthesized and applied to the living-radical emulsion polymerization of methyl methacrylate (MMA) initiated by UV irradiation in the absence of added surfactant and additional initiator at various temperatures. A stable spherical bead of PMMA was successfully obtained using the suriniferter, maintaining the living-radical polymerization characteristics. Monomer conversion, molecular weight evolution and distribution, and final particle sizes were characterized. The higher the iniferter concentration, the higher the conversion and the lower the molecular weight, final particle size, and molecular weight distribution (PDI) obtained. A linear increase in molecular weight with respect to conversion is observed, implying that this technique using the suriniferter follows living-radical polymerization. The PDI varies from 1.21 to 1.43, and the final particle sizes vary from 407 to 304 nm with an increase in the polymerization temperature from 60 to 80 °C. The ratios of the triad tacticity for syndiotactic, atactic, and isotactic configurations of the synthesized PMMA are 54.3, 38.6, and 7.1, respectively, and the glass-transition temperature (T_g) is 126.6 °C, which is much higher than that of commercial PMMA (T_g = 105 °C). Thus, it is believed that the suriniferter used in living-free-radical emulsion polymerization modifies the stereoregularity of the PMMA.

Full text of DOI:10.1021/ma034331i

7994
Macromolecules 2003, 36, 7994-8000
Living-Free-Radical Emulsion Photopolymerization of Methyl
Methacrylate by a Surface Active Iniferter (Suriniferter)
Sa n g Eu n Sh im , Yod a Sh in , J on g Won J u n , Ka n gseok Lee, Hyeju n J u n g, a n d
Soon ja Ch oe*
Department of Chemical Engineering, Inha University, 253 Yonghyundong,
Namgu, Incheon, South Korea 402-751
Received March 17, 2003; Revised Manuscript Received August 11, 2003
ABSTRACT: A novel surface-active RAFT agent as a suriniferter, composed of the dithiobenzoyl main
structure and a benzoic hydrophobic carboxylate hydrophilic moiety, was synthesized and applied to the
living-radical emulsion polymerization of methyl methacrylate (MMA) initiated by UV irradiation in the
absence of added surfactant and additional initiator at various temperatures. A stable spherical bead of
PMMA was successfully obtained using the suriniferter, maintaining the living-radical polymerization
characteristics. Monomer conversion, molecular weight evolution and distribution, and final particle sizes
were characterized. The higher the iniferter concentration, the higher the conversion and the lower the
molecular weight, final particle size, and molecular weight distribution (PDI) obtained. A linear increase
in molecular weight with respect to conversion is observed, implying that this technique using the
suriniferter follows living-radical polymerization. The PDI varies from 1.21 to 1.43, and the final particle
sizes vary from 407 to 304 nm with an increase in the polymerization temperature from 60 to 80 °C. The
ratios of the triad tacticity for syndiotactic, atactic, and isotactic configurations of the synthesized PMMA
are 54.3, 38.6, and 7.1, respectively, and the glass-transition temperature (Tg) is 126.6 °C, which is much
higher than that of commercial PMMA (Tg ) 105 °C). Thus, it is believed that the suriniferter used in
living-free-radical emulsion polymerization modifies the stereoregularity of the PMMA.
In tr od u ction
architecture, and polymerization has been carried out
in bulk or organic media. However, living-radical poly-
merizations carried out in aqueous media15,16 are of
great importance in industrial application. Water as the
reaction medium endows a number of advantages such
as environmental-friendly processes, easy removal of
reaction heat released during polymerization, and fea-
sible handling of the final product because of its low
viscosity.
With regard to the fast development of materials
science, the use of polymeric materials has been exten-
sive, and the design of proper polymeric materials at
the molecular level has become very important. Owing
to the advent of several revolutionized “living”-radical
polymerization methods, synthesizing well-defined poly-
mers/copolymers having a desired structure has come
true in a convenient way; therefore, the subject of the
molecular design of polymers by means of living-radical
polymerization has been a rapidly growing research
area. These methods mainly include nitroxide-mediated
polymerization (NMP),1,2 atom-transfer radical polym-
erization (ATRP),3,4 and reversible addition-fragmenta-
tion chain-transfer polymerization (RAFT).5,6 Among
them, the RAFT process has several advantages over
NMP or ATRP. Unlike NMP or ATRP, RAFT can be
easily applied to a variety of monomers at the same
reaction temperature and with the same method as in
conventional radical polymerization without the need
for an additional catalyst-removal process.7 Therefore,
the discovery of the RAFT process is a breakthrough in
the field of living-radical polymerization.
Because RAFT can be readily applicable to emulsion
or miniemulsion polymerization, intensive studies fo-
cused on conducting living-radical polymerization in a
water medium have been carried out in this field.17-22
As with conventional emulsion polymerization process,
typical ingredients for RAFT emulsion polymerization
are water, water-insoluble monomers, water-soluble
initiators, RAFT agents, and surfactants such as sodium
dodecyl sulfate (SDS). The surfactant is responsible for
the stability of the latex by preventing coagulation
between particles. However, when SDS was used with
RAFT agents in emulsion polymerization, it signifi-
cantly retarded the polymerization rate and a deterio-
rated red layer of low-molecular-weight dormant species
was observed at the beginning of polymerization, sug-
gesting that SDS interacts with RAFT agents.23 To
overcome the problems induced by surfactant, addition-
fragmentation reactive surfactant, so-called TRAN-
SURF, has been designed; TRANSURF acts as both a
chain-transfer agent and a surfactant in the RAFT
emulsion polymerization of MMA.24,25 The basic struc-
ture of TRANSURF consists of three functional
groups: methyl methacrylate dimer acting as a chain-
transfer agent, a long aliphatic hydrocarbon chain
responsible for the hydrophobic moiety, and a sulfate
group attached to the hydrocarbon chain for hydrophi-
licity.
In general, the RAFT process uses various sulfide and
disulfide iniferters (i.e., initiator transfer-agent termini-
tor)8 in conjunction with conventional initiator to confer
a living nature throughout the polymerization. Such
iniferters are classified into photoiniferters bearing a
dithiocarbamyl group9,10 and thermal iniferters carrying
carbon-carbon11,12 or azo13,14 bonds according to the
dissociation locus.
The initial interest in living-radical polymerization
has been focused on the control of polymer molecular
* Corresponding author. E-mail: schoe@inha.ac.kr. Tel: +82-
32-860-7467. Fax: +82-32-876-7467.
10.1021/ma034331i CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/27/2003

Macromolecules, Vol. 36, No. 21, 2003
Photopolymerization of Methyl Methacrylate 7995
Sch em e 1. Syn th esis of 4-Th ioben zoyl Su lfa n ylm eth yl
Ben zoa te
In this study, a novel surface-active RAFT agent, so-
called suriniferter, composed of the dithiobenzoyl main
structure, a benzoic hydrophobic moiety, and a carbox-
ylate hydrophilic moiety was synthesized and applied
to the RAFT emulsion polymerization of MMA initiated
by UV irradiation in the absence of added surfactant
and without additional initiator. Then, the suriniferter
concentration and temperature-dependent polymeriza-
tion characteristics such as the conversion, molecular
weight and distribution, final particle size, and struc-
tural regularity of PMMA latex were studied.
F igu r e 1. 1H NMR spectrum of the synthesized suriniferter.
erization products, including conversion, molecular weight and
distribution, and intermediate particle morphology. After the
completion of polymerization, the resultant latex was frozen
in a refrigerator and became molten at room temperature. The
precipitated phase was collected and dried in vacuo for 24 h.
As a consequence, white PMMA beads were obtained.
Exp er im en ta l Section
Mater ials. Reagent-grade phenylmagnesium bromide, R-bro-
mo-F-toluic acid, and carbon disulfide used in the preparation
of suriniferter were purchased from Aldrich (Milwaukee, WI).
Anhydrous diethyl ether and methanol were purchased from
J . T. Baker Co. (Phillipsburg, NJ ). Carbon disulfide and diethyl
ether were distilled to remove existing impurities and water.
MMA (J unsei Chemicals, J apan) was distilled under reduced
pressure to remove inhibitors and was stored in a refrigerator
prior to use. Double-distilled deionized (DDI) water was used
as a reaction medium.
Syn th esis of Su r in ifer ter . 4-Thiobenzoyl sulfanylmeth-
ylsodium benzoate suriniferter was synthesized in three steps.
First, 0.03 M phenylmagnesium bromide and 0.045 M carbon
disulfide reacted in dry diethyl ether at 10 °C for 6 h. After
removing unreacted reagents by distillation, a 1.7:1 molar ratio
of (thiobenzoyl)sulfanylmagnesium bromide to R-bromo-F-
toluic acid was added to methanol. The second step in the
reaction was carried out at 60 °C for 24 h. Again, unreacted
reagent and methanol were removed by distillation. The
-COOH end group of the product obtained from the second
step was replaced by -COONa via a 1 M NaOH solution that
was used to introduce water solubility into the product so that
it could be used in emulsion polymerization. Details of the
synthesis procedure of the suriniferter are shown in Scheme
1.
Ch a r a cter iza tion s. The chemical structures of the syn-
thesized suriniferter and the obtained PMMA were confirmed
1
with a Varian 400-MHz H NMR using CDCl3 as the solvent.
The molecular weight and polydispersity index (PDI) were
characterized using Waters GPC (gel permeation chromatog-
raphy) equipped with a 510 differential refractometer and a
Viscotek T50 differential viscometer. High-resolution 105, 103,
and 102 Å µ-styragel packed columns were employed. A
universal calibration curve was obtained on the basis of 10
polystyrene standard samples (Polymer Laboratories, U.K.)
with molecular weights ranging from 7 500 000 to 580 g/mole.
PMMA powder dissolved in THF was injected at a flow rate
of 1.0 mL/min. Scanning electron microscopy (SEM, Hitachi
S-4300) was used to study the morphology of the synthesized
PMMA particles. Differential scanning calorimetry (DSC,
Perkin-Elmer DSC-7) was used to investigate the glass-
transition temperature of PMMA. The monomer conversion
to polymer was determined gravimetrically. The number-
average particle diameter, Dn was obtained using Scion Image
Analyzer Software by counting 100 individual particles from
SEM microphotographs.
Resu lts a n d Discu ssion
Scheme 1 shows the synthesis of 4-thiobenzoyl sul-
fanylmethylsodium benzoate for the RAFT agent as a
suriniferter. The color of the reaction solution turned
orange after the completion of the first step of the
reaction, and the final pink powder was obtained after
purification by distillation. The chemical structure of
4-thiobenzoyl sulfanylmethylsodium benzoate was con-
firmed from the proton NMR spectrum as shown in
Figure 1. Scheme 2 represents the polymerization
mechanism of this type of suriniferter in which the
methyl benzoate group acts as an active growing species.
In the absence of a conventional initiator such as
potassium persulfate or ammonium persulfate, the
generation of free radicals is ascribed to the suriniferter
because it plays the role of initiator. Therefore, the term
“iniferter” proposed by Otsu8 would be appropriate in
the absence of a conventional initiator. In this case, a
P olym er iza tion of MMA. Polymerization was carried out
in a 500-mL three-necked reaction vessel equipped with a
mechanical stirrer. The agitation speed was kept at 150 rpm.
Polymerization temperatures were 60, 70, and 80 °C and were
controlled by a water-bath circulator; a nitrogen atmosphere
was maintained throughout the polymerization. A 1-kW UV
lamp having a 365-nm wavelength was employed to initiate
the polymerization. The methyl methacrylate (MMA) concen-
tration was 10 wt % based on the reaction medium, and the
initiator concentration was varied from 0.1 × 10-3 to 1.0 ×
10-3 M. The general procedure was as follows: DDI water and
MMA were combined in a reaction vessel and purged with
nitrogen for 30 min. When the temperature inside the reaction
vessel reached the desired level, the vessel was charged with
suriniferter dissolved in a small amount of water, and the
reaction was initiated by turning on the UV lamp. During the
6-h polymerization, 5 mL of the sample was periodically taken
from the reaction vessel in order to characterize the polym-

7996 Shim et al.
Macromolecules, Vol. 36, No. 21, 2003
Sch em e 2. RAF T Mech a n ism of MMA (M) in th e P r esen ce of Su r in ifer ter
sion of MMA with respect to polymerization time with
0.5 × 10-3 M suriniferter where initiation was intro-
duced by UV irradiation. Because the suriniferter acts
as an initiator, chain-transfer agent, terminator, and
surfactant, the polymerization recipe simply consists of
water, monomer, and the suriniferter. The plot of
conversion versus polymerization time is similar to
those in conventional emulsion polymerization. Conver-
sions of 0.85, 0.89, and 0.91 for 6 h were obtained at
60, 70, and 80 °C, respectively. The higher the temper-
ature, the higher the conversion obtained due to the fast
propagation of the free radicals and possibly due to the
fast decomposition of suriniferter at elevated tempera-
ture. In conventional radical polymerization, it is known
that the activation energy for radical propagation is
appreciably higher than that of termination at higher
temperature.28 Thus, the increase in kp/kt (kp and kt
represent the rate constants at propagation and termi-
nation, respectively) with temperature results in a fast
polymerization rate.
In Figure 3a, the number-average molecular weights
of PMMA in the course of polymerization prepared by
a constant 0.5 × 10-3 M suriniferter are shown as a
function of conversion. It is noted that approximate 60%
conversion was obtained at a very early stage (within 1
h) in the polymerization. Because the polymerization
was so rapid in the beginning stage of the reaction,
samples were taken after 1 h to avoid the artificial
retardation of the polymerization by turning off the UV
lamp. However, it is believed that the living nature is
valid for the beginning stage of the polymerization
because the extrapolated lines of the experimental data
points pass through the origin for all systems.
F igu r e 2. Fractional conversion vs reaction time with a
suriniferter concentration of 0.5 × 10-3 M at various temper-
atures.
radical is produced from the iniferter, and the active
radical is transferred to the iniferter itself; then a
growing species is generated by a reversible addition-
fragmentation mechanism. The active growing moiety
further reacts with monomer, and the radical is trans-
ferred to the dormant chain with the dissociation of
another radical that induces termination. However, in
the presence of initiator, the iniferter would rather act
as a chain-transfer agent, so the “RAFT agent” would
be appropriate. Under UV irradiation of dithioester
compounds, Hong et al.26 suggested a reversible termi-
nation mechanism as an explanation of living behavior.
However, Quinne et al.27 claimed that the reversible
termination mechanism was not adequate compared to
the RAFT mechanism because it was not enough to
differentiate between the two mechanisms regarding the
structure of the polymer obtained and account for the
fate of radicals generated in the monomer.
The higher the polymerization temperature, the higher
the achieved molecular weight, which is opposite to
macroemulsion polymerization using thermal initia-
tors.29 In emulsion polymerization using conventional
thermal initiators, the molecular weight tends to de-
crease with initiator concentration because high tem-
perature induces a high concentration of free radicals
introduced by the decomposition of the thermal initiator,
which facilitates bimolecular termination. The same
trend was reported for the living-free-radical polymer-
P olym er iza tion Ch a r a cter istics a n d F or m a tion
of a Sta ble P MMA Colloid . Figure 2 shows the effect
of polymerization temperature on the fractional conver-

Macromolecules, Vol. 36, No. 21, 2003
Photopolymerization of Methyl Methacrylate 7997
F igu r e 4. GPC traces for PMMA prepared by UV initiation
with 0.5 × 10-3 M suriniferter at 70 °C.
suriniferter concentration of 0.5 × 10-3 M is depicted
in Figure 3b. The final polydispersity index values are
1.23 (0.845 conversion), 1.29 (0.89 conversion), and 1.41
(0.91 conversion) at 60, 70, and 80 °C, respectively. The
polydispersity tends to increase slightly with conversion
and decrease with decreasing polymerization tempera-
ture. Ray et al. reported the decrease in PDI with
respect to conversion both from experiment and simula-
tion.33 However, Quinn et al. found that the polydis-
persity index in RAFT polymerization initiated with UV
radiation increased because of the degradation of the
RAFT agent by UV at prolonged polymerization time.27
In this study, the initiation was also achieved by UV
radiation; therefore, an increase in PDI with conversion
is expected because of the possible degradation of the
RAFT agent.
The evolution of the molecular weight and polydis-
persity of PMMA prepared with 0.5 × 10-3 M surin-
iferter at 70 °C as a function of polymerization time is
shown in Figure 4. It is clearly seen that the GPC
chromatogram shifts to slightly low retention time
owing to increasing number-average molecular weight
but that the polydispersity is not influenced very much
upon polymerization.
F igu r e 3. (a) Number-average molecular weight and (b)
polydispersity vs conversion of PMMA prepared with 0.5 ×
10-3 M suriniferter.
ization of polystyrene using a RAFT agent by thermal
initiation at a series of temperatures: the number-
average molecular weight decreases with temperature30
for this reason. For the controlled radical polymerization
of styrene and acrylate by an alkyl iodide degenerative
transfer agent in the presence of AIBN, the dependence
of molecular weight on polymerization temperature
ranging from 50 to 90 °C was found to be weak.31
In general radical polymerization, the dependence of
the rate of polymerization (Rp) and number-average
degree of polymerization (xjn) on temperature is ex-
pressed as follows:
Figure 5 displays the SEM microphotographs of the
PMMA beads prepared by living-radical emulsion po-
lymerization at 0.5 × 10-3 M suriniferter at 60, 70, and
80 °C. Again, it should be noted that additional surfac-
tant or initiator such as potassium persulfate (KPS) was
not involved. In the presence of surfactant, polymer
particles are formed in spherical micelles and continu-
ously grow in size by monomer transport from droplets
that acts as a monomer reservoir. In surfactant-free
emulsion polymerization, hydrophilic sulfate free radi-
cals generated by the decomposition of persulfate react
with hydrophobic monomer dissolved in the aqueous
phase to form oligomeric free radicals, which can play
a role in micelle formation.34 The mechanism for the
subsequent particle growth is the same as that in the
case where a surfactant is employed. Surfactants are
composed of hydrophobic and hydrophilic parts. Ex-
amples of the hydrophobic moiety are long straight or
branched alkyl groups, alkylbenzenes, and alkylnaph-
thalenes. Examples of the hydrophilic moiety include
carboxyl (RCOO-M+), sulfonate (RSO3-M+), or sulfate
(ROSO3-M+) for anionic surfactants and quaternary
ammonium halides (R4N+Cl-) for cationic surfactants.35
For 4-thiobenzoyl sulfanylmethylsodium benzoate used
in this study, the surface-active group consists of
d ln(Rp) (2Ep + Ed) - Et
)
(1)
(2)
2RT2
dT
d ln(xjn) 2Ep - (Ed + Et)
)
2RT2
dT
where, Ep, Ed, and Et indicate the activation energy of
propagation, initiator dissociation, and termination,
respectively. R and T denote the gas constant and the
temperature. Because the general order of magnitude
of the activation energy is Ed . Ep > Et, (d ln(Rp)/dT)
and (d ln(xjn)/dT) become positive and negative, respec-
tively, when thermally decomposable initiator is in-
volved, whereas they become both positive in the
absence of thermal initiator (i.e., Ed ≈ 0). In addition,
photopolymerization follows the latter case32 where
elevated temperature yields a high rate of polymeriza-
tion and a high number-average degree of polymeriza-
tion, which is directly related to the number-average
molecular weight.
The polydispersity of PMMA during polymerization
with respect to polymerization temperature at a fixed

7998 Shim et al.
Macromolecules, Vol. 36, No. 21, 2003
F igu r e 6. Effect of temperature on the final particle size of
PMMA prepared with 0.5 × 10-3 M suriniferter.
Ta ble 1. In flu en ce of Su r in ifer ter Con cen tr a tion on
P olym er iza tion Ch a r a cter istics a n d P a r ticle Size for
P r ep a r a tion a t 70 °C for 4 Hou r s
suriniferter
conc (M)
particle
size (nm)
Mn (g/mol)
PDI
conversion
0.1 × 10-3
0.5 × 10-3
1.0 × 10-3
413 000
404 000
365 000
1.394
1.321
1.293
0.82
0.89
0.92
412
392
383
explained earlier. The production of stable spherical
PMMA beads prepared in this study is thus attributed
to the suriniferter carrying the carboxyl group.
Figure 6 represents the change in diameter of PMMA
beads shown in Figure 5. In accordance with the
temperature increase from 60 to 80 °C, the particle size
decreases from 407 to 304 nm, which results in a
common observation in emulsion polymerization.
The influence of the suriniferter concentration and
the resultant particle diameter are tabulated in Table
1. As the suriniferter concentration increases from 0.1
× 10-3 to 1.0 × 10-3 M, the number-average molecular
weight, the polydispersity, and the average particle size
decrease, whereas the conversion increases, exhibiting
the same behavior as observed when thermal initiator
is used in conventional or RAFT emulsion polymeriza-
tion. Regarding the reduced particle size, the concentra-
tion of suriniferter and RAFT radical transport should
be considered. The increased amount of initiator (surin-
iferter in this work) induces a large number of polymeric
particles, which leads to small individual particle sizes.
Besides this effect, in the RAFT living-radical emulsion
polymerization of styrene19 and butyl acrylate,36 the
number-average diameter was reported to decrease and
the size distribution became narrower as the concentra-
tion of RAFT agent increased. This result was postu-
lated by the fact that the active growing radicals
produced from the fragmentation of the RAFT agent (or
iniferter) exit the particles and reenter micelles to create
new particles during the nucleation period in interval I
of the emulsion polymerization mechanism. Gilbert et
al. reported that the radical exit rate coefficient truly
increased with increasing amounts of RAFT agent,
resulting in a retardation of polymerization because of
the transport of RAFT-agent radicals to the particles
where polymerization is taking place.18
F igu r e 5. SEM micrographs of PMMA beads prepared with
0.5 × 10-3 M suriniferter at (a) 60, (b) 70, and (c) 80 °C.
hydrophobic benzyl and hydrophilic carboxyl moieties.
By the homolytic cleavage of the carbon-sulfur bond
in the suriniferter by UV irradiation, the methyl ben-
zoate radical as an active growing species initiates
polymerization. The benzyl group in the surfactant
moiety in the suriniferter seems to be too short to play
the role of surfactant in emulsion polymerization.
However, as the length of the oligomeric radical bearing
the carboxyl end group becomes longer by the further
reaction of MMA, the degree of hydrophobicity tends to
increase because the carbon-carbon bond in the oligo-
meric main chain is hydrophobic. This mechanism is
similar to surfactant-free emulsion polymerization, as
Figure 7 displays SEM microphotographs of PMMA
beads prepared by 0.1 × 10-3, 0.5 × 10-3, and 1.0 ×

Macromolecules, Vol. 36, No. 21, 2003
Photopolymerization of Methyl Methacrylate 7999
F igu r e 7. SEM micrographs of PMMA beads prepared with various amounts of suriniferter at 1, 2, and 4 h at 80 °C. (a) 0.1 ×
10-3 M, 1 h; (b) 0.1 × 10-3 M, 2 h; (c) 0.1 × 10-3 M, 4 h; (d) 0.5 × 10-3 M, 1 h; (e) 0.5 × 10-3 M, 2 h; (f) 0.5 × 10-3 M, 4 h; (g) 1.0
× 10-3 M, 1 h; (h) 1.0 × 10-3 M, 2 h; and (i) 1.0 × 10-3 M, 4 h.
10-3 M suriniferter concentrations at 1, 2, and 4 h at
80 °C. In all cases, stable spherical PMMA beads are
successfully produced. These particles are formed in an
early stage of polymerization and subsequently grow.
Because the conversions are different with respect to
suriniferter concentration (i.e., a lower concentration of
suriniferter yields a low conversion), it is not reasonable
to compare the particle sizes depending on the polym-
erization duration. On the basis of Figure 7, it is seen
that the suriniferter used in this study produces stable
PMMA colloids without any additional surfactant or
initiator.
P r op er ties of P MMA La tex. The 1H NMR spectrum
of PMMA prepared with 1.0 × 10-3 M of suriniferter at
80 °C is seen in Figure 8; it shows three distinct peaks
appearing at the highest field, which represent meth-
acrylate methyl groups of different tacticity.37 The bands
at about 0.82, 1.02, and 1.18 ppm arise from syndiotactic
F igu r e 8. 1H NMR spectrum of the obtained PMMA.
(rr), atactic (mr), and isotactic (mm) methyl groups,
respectively.37 From Figure 8, the tacticity of the PMMA
was calculated from the integrated ratios of rr, mr, and
mm. The ratios of the triad tacticty for syndiotactic,
atactic, and isotactic are 54.3, 38.6, and 7.1, respectively.
The relatively regular molecular structure of the PMMA
particles was expected to affect the thermal properties
or characteristics. From Figure 9, we have observed that
the glass-transition temperature (Tg) of the obtained
PMMA is about 126.6 °C, which is much higher than
that of commercial PMMA (Tg ) 105 °C).38 The syndio-
tacticity of the PMMA sample prepared in this study is
54.3%, which is higher than that of commercial PMMA
bearing 43%.38 The higher ratio of syndiotacticity results
in a relatively regular structure and leads to an increase
in the glass-transition temperature. It has been known
that the glass-transition temperature of PMMA greatly
depends on the tacticity of the polymer. In general, the
glass-transition temperature of PMMA is proportional
to the degree of syndiotacticity and inversely propor-
tional to the degree of isotacticity. The glass-transition
temperature of PMMA was reported to increase from
41.5 to 125.6 °C for syndiotacticity/atacticity/isotacticity
triads of 0/5/95 and 64/36/9.39
Thus, we believe that the use of suriniferter with
living-free-radical emulsion photopolymerization can
induce different tacticity in PMMA. This is the first
observation in the present study. However, the exact

8000 Shim et al.
Macromolecules, Vol. 36, No. 21, 2003
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mechanism for the variance in the tacticity is not yet
clarified; therefore, it is under investigation.
Con clu sion s
(17) Le, T. P.; Moad, G.; Rizzardo, E.; Thang, S. H. WO 9801478,
1998.
A novel surface-active RAFT agent as a suriniferter,
composed of 4-thiobenzoyl sulfanylmethylsodium ben-
zoate, was successfully synthesized and applied to the
RAFT emulsion polymerization of methyl methacrylate
initiated by UV irradiation in the absence of added
surfactant or additional initiator. The suriniferter con-
centration and temperature-dependent polymerization
characteristics such as the conversion, molecular weight
and distribution, final particle size and distribution, and
molecular regularity were studied. The higher the
iniferter concentration, the higher the conversion and
the lower the molecular weight and molecular weight
distribution (PDI) and final particle size obtained. A
linear increase in molecular weight with respect to
conversion is observed, implying that this technique
using suriniferter follows living-radical polymerization.
The PDI varies from 1.21 to 1.43, and the final particle
sizes vary from 407 to 304 nm with an increase in
polymerization temperature from 60 to 80 °C. The ratios
of the triad tacticty for the syndiotactic, atactic, and
isotactic synthesized PMMA are 54.3, 38.6, and 7.1,
respectively, and the glass-transition temperature (Tg)
is 126.6 °C, which is much higher than that of the
commercial PMMA (Tg ) 105 °C) having 44% syndio-
tacticity. Higher ratios of syndiotacticity result in
relatively regular structure, hence leading to an increase
in the glass-transition temperature. Thus, it is believed
that the suriniferter used in living-free-radical emulsion
polymerization modifies the tacticity of PMMA.
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Ack n ow led gm en t. This work was supported by an
NRL (National Research Laboratory of the Ministry of
Science and Technology in Korea) project (grant no.
M10203000026-02J 0000-01410, 2002-2007) and was
partially supported by the Korea Research Foundation
(grant no. KRF-2001-041-E00500).
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Refer en ces a n d Notes
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(2) Georges, M. K.; Veregin, R. P. N.; Kazmaier, P. M.; Hamer,
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