Embed Size (px)
Citation preview
Full Terms & Conditions of access and use can be found athttp://www.tandfonline.com/action/journalInformation?journalCode=gpss20
Download by: [Hacettepe University] Date: 06 April 2017, At: 03:54
Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Microemulsion and macroemulsionpolymerization of octamethylcyclotetrasiloxane: Acomparative study
Jaber Khanjani, Mohammad Zohuriaan-Mehr & Shahla Pazokifard
To cite this article: Jaber Khanjani, Mohammad Zohuriaan-Mehr & Shahla Pazokifard(2017): Microemulsion and macroemulsion polymerization of octamethylcyclotetrasiloxane:A comparative study, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:10.1080/10426507.2017.1315418
To link to this article: http://dx.doi.org/10.1080/10426507.2017.1315418
Accepted author version posted online: 05Apr 2017.
Submit your article to this journal
View related articles
View Crossmark data
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 1
Micro- and macro-emulsion polymerization of D4
Microemulsion and macroemulsion polymerization of octamethylcyclotetrasiloxane: A
comparative study
Jaber Khanjania, Mohammad Zohuriaan-Mehr a,* and Shahla Pazokifardb
aAdhesive and Resin Dept., Iran Polymer and Petrochemical Institute,
Tehran, Iran
bColor & Surface Coatings Dept., Iran Polymer and Petrochemical Institute,
Tehran, Iran
*Email: [email protected]
Abstract
Octamethylcyclotetrasiloxane (D4) was polymerized in a microemulsion system using novel
formulations, in which acrylamide was involved as a co-emulsifier. Dodecylbenzene sulfonic
acid was used as both a cationic initiator and emulsifier. The effect of emulsifiers, D4, feeding
rate and temperature on conversion, polymerization rate (Rp), latex stability and particle sizes
were investigated. A conventional (macroemulsion) system was also studied comparatively. Rp
in the microemulsion was quickly increased to a maximum of 0.108 mol L-1
s-1
at ~30 min
corresponding to a conversion of ~38%, and then decreased with reaction progression over a
period of 30–110 min. In the macroemulsion system, however, a constant rate was observed
between conversion 30 and 50%, and its optimal sample contained an average particle diameter
of 88 nm while that from microemulsion had smaller particles with diameter of 19 nm.
Activation energies were also estimated to be 31.5 and 41.1 kJ/mol for the microemulsion and
macroemulsion systems, respectively.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 2
Key words
octamethylcyclotetrasiloxane, micro-emulsion polymerization, acrylamide, particle size, PDMS
latex
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 3
INTRODUCTION
Silicones with various microstructures and architectures are useful in industry mainly due to their
lack of toxicity, elasticity and hydrophobicity [1-4]
. The ring-opening polymerization of
octamethylcyclotetrasiloxane (D4) and/or the copolymerization of D4 with functional siloxane
monomers can be used to prepare a wide variety of silicones [2]
.
Compared to the classical ionic polymerization of cyclosiloxanes in bulk or in solution,
the final conversion of cyclosiloxanes polymerized in emulsion is higher. Meanwhile, linear
polymers with higher molecular weight, and narrower distribution, can be obtained from
emulsions with less cyclic by-products [5-8]
. The main reaction stages of cyclosiloxanes in
emulsion are the ring-opening polymerization (ROP) of cyclosiloxane monomers followed by
the condensation polymerization of the linear oligomers. Moreover, many subordinate reactions
such as branching, redistribution and cross-linking of chains, all have great influence on the final
conversion, molecular weight and distributions [7-9]
.
Since Hyde and Wehrly first reported the synthesis of dihydroxylated
polydimethylsiloxane (PDMS) latex in 1959, ionic polymerization in emulsion has attracted
much attention in recent years [10-17]
. Many monomers, especially cyclosiloxanes, have been
reported to generate polymer latexes by ionic polymerization method [5, 13-17, 18-23]
. For the
preparation of latexes based on PDMS, there are mainly three emulsion-polymerization methods,
namely, conventional (macroemulsion) polymerization, miniemulsion polymerization and
microemulsion polymerization [2]
.
Conventional emulsions are characterized by opaque latexes having a large particle size
(typically greater than 300 nm) [17]
. However, by imposing high shear on the emulsion system
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 4
prior to the polymerization, latexes with particle sizes in the order of 50–500 nm prepared by the
miniemulsion polymerization are stable [2, 5, 15, 16]
and their appearance are usually identified by
slightly opaque to slightly translucent. Compared with the above two latexes, the latexes from
microemulsion are the most transparent and their particle sizes are in order of 0–100 nm [2, 12-16]
.
Many improvements have been achieved in microemulsion polymerization to synthesize
polysiloxanes [1, 13, 24-27]
after Stoffer and Bone reported on them in 1980 [25]
. However, the
monomer content was relatively low and the content of emulsifier and co-emulsifier were too
high in the microemulsion system. In order to overcome these deficiencies, many approaches
have been developed. For example, in another study, ionic and non-ionic emulsifiers were
dissolved in water, and then added the monomer to the solution drop by drop. After a catalyst
was added to initiate the reaction, the microemulsion with relatively low emulsifier content was
obtained [12, 19]
. Other researchers discussed the effect of nature and amount of co-emulsifiers on
the microemulsion polymerization of D4 [1]
. Later, some researchers [29, 30]
used silicone
surfactants as emulsifiers and achieved favorite emulsifying effect. Additionally, some
polymerization methods like seeded microemulsion polymerization [31]
and semi-continuous
microemulsion polymerization [32]
were also used to improve the solid content. Also, there have
been many reports on the microemulsion polymerization of cyclosiloxanes with cationic or
anionic surfactants as emulsifiers [14, 15, 33, 34]
using either basic (anionic) [35-37]
or acidic (cationic)
[5, 38-40] catalysts. Meanwhile, there have been only a few studies on the microemulsion
polymerization of siloxanes with nonionic surfactants as emulsifiers. In another work it was
reported a nonionic PDMS emulsion with a mean droplets particle size of ~65 nm from the
emulsion polymerization of D4, with a nonionic surfactant and an organosilanolate as the
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 5
initiator [41]
. It was prepared an oil-in-water polysiloxane microemulsion with a particle size of
15.1 nm, with ethoxylated lauryl ether as the surfactant and 1-pentanol as the co-surfactant in
another project [16]
. It seems that polymerization in microemulsions with high solid contents and
low surfactant amounts are difficult. Moreover, the microemulsion polymerization rate (Rp) of
siloxane with nonionic surfactants as emulsifiers is slower than that of ionic surfactants. On the
other hand, some groups studied the kinetics or mechanism of polymerization in emulsion.
Recently, the effect of drop sizes on the polymerization rates was studied in a miniemulsion, and
a three-layer oil/water interface model was proposed [5]
. Meanwhile, Zhuang et al. [1]
investigated
the particle kinetics and mechanism of polymerization of D4 in microemulsion. Polysiloxane
latexes were prepared by microemulsion polymerization of D4 with octadecyl trimethyl
ammonium chloride as a cationic emulsifier and potassium hydride as an initiator in another
study, particle sizes were determined and the kinetics by the initial-rate method was studied [13]
.
Considering the literature of PDMS latexes up to now, in this article, we looked into this
subject from another viewpoint. In other words, after optimization of the conventional emulsion
polymerization using dodecylbenzene sulfonic acid as an acidic catalyst, D4 as siloxane
monomer and a hybrid of nonionic and anionic emulsifiers, we used acrylamide as a co-
emulsifier. Thus, the synthesis of PDMS latexes with polymer particles of less than 80-nm
diameter and high solid content was investigated, while the microemulsion polymerization was
optimized by altering the co-emulsifier content, feeding rate, anionic emulsifier content and
temperature. The kinetics of the conventional and microemulsion polymerization of D4 was also
studied, and particle size of the latexes was comparatively investigated.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 6
RESULTS AND DISCUSSION
The Macroemulsion Polymerization
Optimization of D4 conventional polymerization in order to obtain PDMS polymers with high
conversion and stable latexes were carried out in various amounts of the factors affecting
polymerization process namely DBSA content, emulsifiers type and content, D4 concentration,
temperature and agitation speed (Table 1).
As shown in Figure 1a, the monomer conversion increased to 70-90% for the period of
180 min, reaching the high point of ~90% in DBSA concentration of 0.03 mol/L (Run SL3, Table
1), and then showing a substantial decrease (Figure 1b). An increase in the trend in conversion
with the upsurge in DBSA concentration to 0.03 mol/L can be attributed to the fact that the
concentration of the active sites of polymerization increased with the increase in the
concentration of the initiator, because DBSA acts as both initiator and emulsifier (insurf;
simultaneous role of either initiator or surfactant) [5]
. However, with concentrations of DBSA of
greater than 0.03 mol/L, the conversion decreased because of the probable hindering and special
effect of the DBSA molecules in the intersection of the aqueous/organic phases [13]
.
Furthermore, an investigation of the changes in the conversion percentage during the
reaction showed that with an increase in the acid catalyst concentration to 0.03 mol/L, the rate of
the reaction considerably increased to 0.074 mol L-1
s-1
and after that it decreased with increase in
acid concentration (See section 4.3).
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 7
Our investigations have proven that if anionic emulsifiers such as dioctyl sulfosuccinate
(DOSS) and sodium vinyl sulfonate (SVS) separately be used in the polymerization formulation
without using nonionic emulsifiers, the polymerization system will be unstable. For example, as
for SVS being an anionic active emulsifier, the results showed that in order to design a stable
emulsion polymerization system, the amount of this emulsifier should be limited to less than
0.75% w/w relative to total weight of the monomers in the polymerization formulation.
Otherwise, the synthesized latex will be unstable and along with large visible particles which are
likely the results of the homogeneous emulsion polymerization being occurred outside of the
micelles [42]
.
Anionic emulsifiers like DOSS and SVS are sensitive to the low pH (1-4) values and
electrolyte ions in a way that it is too difficult to control the stability during the polymerization.
Meanwhile, when anionic emulsifier is used, the surface of the particles will be electrically
charged, resulting in the production of an electrostatic force between the surface of the particles
and, finally, emulsifier ion causing a static tension. Therefore, the negative charge on the surface
of the latex causes the entrance of the free radicals into the particles to be difficult, resulting in
reduction of the rate and yield of the polymerization. Although using a nonionic emulsifier like
NP-20 can reduce the static tension by formation of a protecting hydrolysis layer onto the latex
particles, the size of the particle is so large that the latex particles keen on the precipitation due to
the high molecular weight causing the shelf life of the latex to be unfavorable. As a result, in
order to do the polymerization process successfully and produce a latex with appropriate
stability, making a stable pre-emulsion is required and for that, a mixture of anionic and nonionic
emulsifiers is used so as to have an alternative static tension effect on the surface of the latex
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 8
particles causing the stability of the particles and polymerization. As clearly seen in Figure 1c,
with an investigation on the effect of the emulsifier type on polymerization conversion, it can be
concluded that in the presence of the mixture emulsifiers consisting of anionic emulsifier SDS
and nonionic emulsifier NP-20 with the ratio of 3:1 w/w, D4 polymerization was progressed with
higher yield of conversion in comparison with other blend emulsifiers. This hybrid emulsifying
system was found to improve the polymerization rate up to 0.11 mol L-1
s-1
(See section 4-3).
In order to investigate the effect of hybrid emulsifier concentration on the polymerization
reaction of D4, different concentrations relative to monomers’ weight namely 1, 2, 3, 4 and 5%
were selected for the macroemulsion polymerization (Figure 1d). As shown in the figure, it was
observed that with decrease in the concentration of the emulsifiers, conversion yield of
polymerization was decreased, although this decrease was not noticeable up to the approximate
concentration of 2% and we can still observe high conversions of D4 polymerization. However,
in the lower concentrations, yield of polymerization was noticeably decreased and high
percentages of D4 monomer was seen as oil layer on the top of the synthesized latex indicating
an unstable polymerization.
Based on the general theory of the emulsion polymerization [43]
, we know that the size of
the latex particles continuously grows during the polymerization. Thus, more emulsifier
molecules are needed in order that the polymerization remains stable. According to our
experience, the lower content of the emulsifier resulted in less number of particles with larger
sizes. In this state, the bluish shining cannot be practically seen. When polymerization advances
further, more emulsifier molecules cannot be adsorbed on the surface of the latex particles. As a
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 9
result, the ratio of the protected surfaces by emulsifier molecules decreases causing unstable
polymerization or even separation of the monomer droplets from micelles. But, if the amount of
emulsifiers used is more than what needed, number of the latex particles is increased and particle
size highly is decreased; it means that surface area is considerably enlarged. Thus, intermolecular
reaction is so important and quickly increased viscosity causing the dispersion and continuing of
the polymerization reaction to be difficult [42]
.
In spite of this fact that with increase in emulsifier content we would observe more stable
polymerization, considering this fact that emulsifier presence in film formation of the latex
would cause some defects in the resultant latex film and deteriorate the physical-mechanical
properties by their removal during time, the lowest possible amount of emulsifiers was used.
Thus, the lowest possible concentration of the hybrid emulsifier SDS/NP-20 (i.e., 2 wt%; SL10,
Table 1) in which successful polymerization is processed with high conversion yield was
selected as the optimized level of emulsifier in the D4 polymerization formulation.
Regarding the D4 monomer concentration (Table 1), our investigations also showed that
with increased D4 to the extent of 20% relative to the total weight of the formulation (i.e., SL12,
Table 1), the rate of D4 monomer consumption increases, but in its higher concentrations,
polymerization yield was decreased, and practically, the non-reacted monomers were observed
as oil layer on the top of the latex (runs SL15 and SL16).
In the temperature series of experiments (Table 1, Runs SL17-SL20), the polymerization
was run at the range of 70-90oC. As expected, with an increase in the temperature, the final
conversion increased to 91%. Meanwhile, based on the Arrhenius equation, the apparent
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 10
activation energy of D4 macroemulsion polymerization was estimated to be 41.1 kJ/mol. It will
be discussed in comparison with that of the microemulsion system in the next part of the article
(section 4.2).
In order to investigate the effect of agitation rate, as an important factor affecting the
polymerization rate and conversion, the reaction was performed under different stirring speed
.The highest and the lowest conversion of the polymerization (94 and 86%) were observed in the
speeds 110 and 190 rpm, respectively. According to the Arai theory [44]
, this observation can be
explained by considering monomer mass transfer from monomer droplets to the polymer
particles formed in the aqueous phase.
3.2. The Microemulsion Polymerization
Numerous reactions were designed to relatively optimize the level of the factors affecting
microemulsion polymerization for achieving PDMS latexes with small particles and high
polymer content (Table 2). Thus, by means of instantaneous measuring the conversion during the
polymerization, optimized level of that factor was determined.
The effect of the amount of D4 on the consumption of monomer during polymerization
was investigated. It was found out that higher conversions and Rp were obtained when D4
concentration was increased, reaching to a maximum conversion of approximately 85% and Rp
of 0.073 mol L-1
s-1
in a concentration of 6.7×10-4
mol/L.
In emulsion polymerization, it has been reported that some compounds like acrylamide
(AM) can help to achieve particles below 100 nm. For instance, the polymerization of
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 11
hyhydrophobic monomers such as styrene and AM can be exemplified [45, 46]
. To the best of our
knowledge, no report on AM as co-emulsifier was found for D4 polymerization. Thus, the effect
of AM on polymerization of D4 was studied to achieve nano-sized particles smaller than 50 nm.
Different concentrations of AM from 0 to 0.126 mol/L were examined. As shown in
Figure 2a and in Table 2, AM favored either increasing the polymerization rate (Rp) or the
conversion increase. In fact, AM presence had significant effect on conversion (e.g., increasing
from 68 to 88%), as well as considerable effect on Rp as high as 30% (i.e., from 0.070 to 0.091
mol L-1
s-1
). To explain the role of AM as co-emulsifier, it had to be somehow polymerized to
form some oligomeric or polymeric species, as previously reported for the free-radical initiating
systems [45-47]
. Similar suggestions may be preliminarily given here. Under the reaction
conditions, DBSA and/or SDS can probably form some free-radical species being able to initiate
AM polymerization. To empirically examine this probability, the emulsion reaction was run in
absence of D4 monomer under the same conditions as the one used for D4 microemulsion
polymerization while the AM dosage increased to some extent. The synthesized latex was
precipitated in excess methanol, washed, dried, and spectrally analyzed by FTIR. The spectrum
was totally similar to that of reference spectrum of polyAM. Although the reaction conversion
was not high, ~30%, it could prove that polyAM had been formed. This is an imperial evidence
for forming polymeric species from the monomer AM to act as a co-emulsifier in our D4
microemulsion polymerization.
On the other hand, hydrogen transfer polymerization of AM to form low molecular
weight poly(β-alanine) may also be happened via a Michael addition mechanism [48]
. The
assuming oligoAM and/or oligo(β-alanine) species will then help in combination with the main
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 12
emulsifiers (DBSA and SDS) to improve the emulsification process to accelerate the
polymerization leading to latexes with nano-sized particles (~20-50 nm). It should be mentioned
that effect of the changes of SDS on either conversion or particle size was negligible, so its level
was kept unchanged in majority of our experiments.
Increasing DBSA concentration from 0.041 to 0.155 mol/L, an increasing trend in
conversion and Rp to reach conversion 87% and Rp 0.104 mol L-1
s-1
. More DBSA
concentrations, however, had nearly no significant effect on the conversion and Rp. According to
Figure 2b, the amount of 0.08 mol/L was chosen as a favorable concentration of DBSA, because
more and less than this value the conversion was diminished. Actually, with DBSA increasing,
more living chain forms per unit time, consequently, the reaction rate increases, but Rp
decreased after a maximum. In ionic emulsion polymerization, an initiator such as DBSA is also
an emulsifier, which could form micelles, with all the catalytic active groups assembled on the
interface between water and siloxane, and DBSA cannot be inserted in this interface in
concentrations more than 0.08 mol/L to catalyze the ring opening polymerization of D4 [13, 14]
.
According to data given in Table 2, the pre-emulsified monomer feed rate showed no
significant effect on both conversion and Rp. However, it influenced the particle size, so that the
smallest particles (i.e., 28 nm) was obtained from the experimental series of “feeding rate” where
the feed rate was 55.92 g/h. On the other hand, the trend of conversion variation versus reaction
time showed that a lower rate of feeding caused achieving a higher conversion in a shorter time
(Figure 2c, the pre-emulsified monomer feeding rate of 37.28 g/h). It is known that too high
feeding rate leads to a polymerization of a Winsor I mixture that produces similar particle
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 13
diameters and, on the other hand, using a too low addition rate does not produce smaller particle
diameter either [12]
.
The emulsion polymerization of D4 was also carried out at different temperatures 70, 75,
80, 85 and 90 °C. As expected, the higher the temperature, the faster the polymerization reaction
(Table 2, Run MSL19-MSL22). The Rp values showed that the rates of microemulsion
polymerizations are highly affected by temperature, increasing from 0.085 mol L-1
s-1
(at 70 °C)
to 0.145 mol L-1
s-1
(at 90 °C). Figure 2d clearly exhibits the effect of the reaction temperature on
the overall trend of the polymerization progression.
Based on the Arrhenius equation, the apparent activation energy of D4 microemulsion
polymerization was estimated to be 31.5 kJ/mol while it was determined to be lower than that of
the conventional (macroemulsion) counterpart, 41.1 kJ/mol (Figure 3).
The difference on the apparent activation energies means that the reaction capacity of the
monomer is affected by the emulsification systems. The effective initiator, H+ from SO3H)
groups of DBSA), and the correspondingly active centers in an ion-pair form would prefer to
stay in the aqueous phase close to the micelle surface. It is rational to presume that at the
interface, the monomers were initiated and propagated at different rates. Those just nearby to the
aqueous phase should have a higher reactivity than those discarded from the interface by the
hydrophobic tails of surfactant molecules [5]
.
In our microemulsion system in the presence of AM, as mentioned before, we
preliminarily suggested formation of some oligoAM and/or oligo(β-alanine) species in similarity
with those of previously reported [45-48]
. Since these species are totally soluble in water, they can
approach near the micelles; adjacent the hydrophilic outer heads of the surfactants. This may
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 14
result in partial disruption of the micelles leading to decreased coverage of surfactants on the
micelle surface making monomer molecules reaching the surface easier, which leads to an
overall increasing monomer-to-initiator accessibility. Correspondingly, the apparent activation
energy of the polymerization reaction in our microemulsion system decreased. Consequently,
according to the above mention discussion, the micelles disrupted by the assumed AM-based
oligomeric species forms smaller micelles leading to final smaller particles (19-59 nm) produced
from our microemulsion systems (Table 2). That is why the reaction run at lower temperature
yielded lower particle sizes as given in run MSL19-MSL22 in Table 2.
The particle size of representative samples obtained from both polymerization
formulations, e.g. the run SL21 (Table 1) and the run MSL19 without AM (Table 2), were
determined to be 88, and 109 nm, respectively. AM as a co-emulsifier made it possible to
achieve the particle size scales less than even 50 nm, i.e., a successful microemulsion
polymerization was attainable by incorporation of AM. In fact, while the macroemulsion system
gave latexes having particles larger than 80-100 nm, the AM-containing microemulsion system
produced particles sizes below 20-25 nm. The effects of different parameters such as DBSA and
the co-emulsifier concentration, D4 concentration, temperature, and feeding rate on the latex
particles sizes were studied and the data are tabulated in Table 2. Figure 4 representatively shows
the significant differences of our macro- and micro-emulsion systems studied. In addition to the
particle size reduction, the size distribution was also significantly reduced for the particle of the
latexes from the microemulsion system. For the samples from the runs MSL22 and SL21, for
example, the distribution width was measured to be 6.3 and 60 nm, respectively. Meanwhile, the
physical appearance of the different latexes are also representatively exhibited in Figure 4 to
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 15
visually reveal discrepancies of the products obtained from the different dispersion
polymerization reaction systems, i.e. macroemulsion (opaque, milky color) and microemulsion
(semi-transparent).
Under our reaction circumstances, while the particle size changes in lieu of the monomer
concentration were marginal, influence of the feed rate, temperature and particularly emulsifying
system were recognized to be remarkable.
The concentration of the initiator, DBSA, had minor effect on final particle size while the
particle size was increased dramatically as the temperature rises and the lowest particle size, 19
nm, was obtained at 70 ˚C (Table 2). The content of the emulsifier and co-emulsifier
dramatically influenced the final particle diameter, reaching to lowest particle diameter, 40 nm,
in the SDS and AM amounts of 3.3% and 2.5% relative to the weight of the D4 monomer,
respectively (Table 2, run MSL10). So, mixture of emulsification effect of SDS and AM in
combination with DBSA itself was used to decrease the particle diameter and tune the final
particle diameter.
The pre-emulsified monomer feeding rate seems to be another parameter to control the
final size of particles. Too high a feeding rate leads to a polymerization, phenomenon called as
Winsor I mixture [12]
, that produces similar particle diameters, 37 nm (run MSL18). On the other
hand, using a too low rate of addition did not produce smaller particle diameter either. An
optimized feed rate, i.e, 55.92 g/h, was thus needed to produce very small particles, 28 nm (run
MSL18).
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 16
3.3. The Polymerization Kinetics
In order to comparatively demonstrate the general kinetics of macroemulsion and microemulsion
polymerization of D4, the polymerization rate (Rp) obtained by differentiating the conversion
was plotted versus the reaction time as well as against conversion (Figures 5 and 6).
As shown in Figure 5b, the polymerization rate increases quickly to the maximum following the
reaction progression. From Figure 5c, one can find that the polymerization rate reaches its
maximum at about 30 min corresponding to a conversion of about 0.38, and then decreases with
reaction progression in the period of about 30–110 min. The polymerization rate keeps constant
after that. The continuous increase of the polymerization rate in the first interval can be attributed
to the rapid and continuous increase of the amount of the latex particles from zero, which leads
to nucleation. In the nucleation period, the active ions can migrate into the micelles and swell the
micelles to form the particles and the new particles. In addition, there is enough emulsifier to
stabilize the new particles and the micelles do not vanish in the microemulsion polymerization
[1].
Therefore, there is not constant reaction rate period in the microemulsion polymerization process
as shown in Figure 5c, which is different from that of the macroemulsion polymerization; Figure
6c. Moreover, with the polymerization progress, the difference of the surfactant concentration
between the micelle and the latex particle is decreased to a constant level and the polymerization
rate also changes as shown in Figure 5b.
To interpret the changes in rate of reaction in macroemulsion system versus time and conversion
evolution, Figures 6b and 6c, it may be assumed that the polymerization rate depends on the
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 17
number of active polymerization sites at the particle surface where the propagation occurs, and
on the monomer concentration [5]
. It should be stated that at the beginning of the polymerization,
i.e. before the quasi-steady state is reached, the polymerization rate is influenced by the
increasing of number of active polymerization sites and by the decreasing of monomer
concentration at the particle surface. As long as new particles are formed, the monomer
concentration at the particle surface is higher than that defined by equilibrium monomer/polymer
solubility. Nevertheless, the polymerization rate has been found to be constant also during the
period of linear instantaneous conversion increase, except at the very beginning when
progressive nucleation took part and polymerization rate increased from zero value (Interval I).
When the equilibrium monomer/polymer solubility was reached, the quasi-steady state occurred
[1]. The polymerization rate was found to be constant during the whole quasi-steady state period
(Interval II; growth of latex particles). Therefore, the number of active polymerization sites and
the monomer concentration remained unchanged. On the other hand, a constant number of active
polymerization sites mean all the emulsifier is trapped at the surface of existing polymer
particles. After all the monomer was added to the reactor, batch conditions predominated and the
polymerization rate decreased (Interval III) due to decrease of monomer concentration at
propagation sites.
4. CONCLUSIONS
The optimized sample with regard to polymerizations conversion yield, polymerization stability,
Rp and final latex stability, synthesized by macroemulsion polymerization, was studied with
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 18
regard to particle size and its average particle diameter was 88 nm. Particle size study in
microemulsion polymerization process showed that the particle size declined slightly as the
amount of monomer increased. The concentration of initiator, DBSA, had little effect on final
particle size of microemulsion while the particle size increased dramatically as the temperature
rose and the lowest particle size, 19 nm, was obtained at 70˚C. The content of the emulsifier and
co-emulsifier dramatically influenced the final particle diameter, reaching to lowest particle
diameter, 40 nm, in the SDS and AM amounts of 3.3% and 2.5% relative to the weight of the D4
monomer, respectively.
Investigation of the changes in conversion evolution during the reaction showed that with
an increase in acid catalyst concentration to 0.03 mol/L in macroemulsion polymerization and
0.08 mol/L in microemulsion polymerization, the rate of the reaction considerably increased to
0.074 and 0.108 mol L-1
s-1
, respectively. After that, it decreased with increase in acid
concentration. In the microemulsion system, it was clearly seen that with increase in the SDS and
AM concentrations as emulsifier and co-emulsifier, higher conversions were obtained and there
was seen an increasing trend in the rate of microemulsion polymerizations, so that Rp increased
continuously form 0.073 to 0.085 mol L-1
s-1
as for SDS different levels of concentrations and as
for AM co-emulsifier it reached to a maximum in 0.091 mol L-1
s-1
, then it decreased to lower
level of 0.070 mol L-1
s-1
.
Overall, according to the present study on our particular systems, it should be concluded
that the conditions to achieve the desirable latex products are as follows:
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 19
Macroemulsion system: D4 0.67 mol/L, SDS/NP-20 2% relative to total weight of the
monomer, DBSA 0.03 mol/L, 90 oC, 3h. Under these conditions Rp 0.126 mol L
-1s
-1, conversion
91%, particle size 88, and distribution width 60 nm were achieved.
Microemulsion system: D4 0.62 mol/L, DBSA 0.08 mol/L, SDS 0.021 mol/L, AM 0.094
mol/L, pre-emulsified monomer feed rate 55.92 g/h, 90 oC, 3h. Under these conditions Rp 0.085
mol L-1
s-1
, conversion 81%, particle size 19 nm, and distribution width 6 nm were achieved.
Apparent activation energy of the microemulsion and macroemulsion systems were also
estimated to be 31.5 and 41.1 kJ/mol, respectively. Although no other work has considered
acrylamide (AM) as a co-emulsifier for D4 microemulsion polymerization so far, we
investigated the effect of AM as a coemulsifier and finally reached to stable microemulsion
PDMS latex with high conversion and small particle size, lower than 50 nm. Considering
emulsifier amount reported (even up to 50 wt% of the D4 monomer) for D4 microemulsion
polymerization, the total emulsifier amount in solid content of our latexes (sum of SDBS, SDS
and AM ~8-13 wt% of the monomer) is much lower than the reported ones (e.g., references 1
and 13). So, a little AM (as low as 0.4-2 wt%) along with other emulsifies simply favored
achieving microemulsions with particle sizes lower than 50 nm.
As a part of our plan to prepare improved water-borne coatings, this applied research is in
progress towards latexes with ability to form surface coatings having dirt pick-up resistance.
Experimental
Materials
Octamethylcyclotetrasiloxane (D4, SiSiB SILICONES, Korea) and dodecylbenzene sulfonic acid
(DBSA, Merck) were used without further purification. Sodium bicarbonate (Merck) was used as
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 20
buffer for adjusting the pH. The emulsifiers, sodium dodecylsulfate (SDS), acrylamide (AM) and
nonylphenol ethylene oxide-20 units (NP, Iconol NP-20; BASF), dioctyl sulfosuccinate (DOSS,
Merck), sodium dodecylbenzene sulfonate (SDBS) and sodium vinyl sulfonate (SVS) were also
used as received. Deionized water was used to prepare all the solutions and emulsions.
Conventional Polymerization
Conventional polymerization was performed with a semi-batch addition method of pre-
emulsified monomer addition process using a round bottomed 250-mL glass reactor equipped
with a reflux condenser, steel propeller agitator, sampler system and two feeding inlets. First, the
reactor was charged with the predetermined amounts of water and initiator according to Table 3.
Then, it was heated to 83 ºC using an oil bath while stirring at 250 rpm under a nitrogen
atmosphereto exclude air. D4 monomer was then continuously added over 4 min resulting in the
formation a milky white pre-emulsion after 15 min of mixing. The total amount of the pre-
emulsion was continuously fed into the reactor with the rate of 0.71 mL/min in the first hour and
1.60 mL/min for the next 2 h while emulsion polymerization was being performed under the
effective agitation.
After the addition of the total pre-emulsion was completed in the period of 3 h, the
reaction was continued for an extra hour in order that it was made sure that the reaction was
complete. Then, the synthesized latex was cooled to room temperature and was filtered through a
53-μm sieve for the calculation of coagulum content. In order to calculate the rate and the
conversion of the polymerization during the reaction progression, 1-2 g samples were taken from
the reaction medium every 30 min. When the sample was taken and put onto the glass, the
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 21
reaction was stopped with addition of 7 ppm hydroquinone aqueous solution. Then, the polymer
was coagulated with the addition of 2 drops of ethanol and dried (140 oC, 1 h).
Microemulsion Polymerization
Polysiloxane microemulsions were prepared in a 500-mL four-neck flask equipped with a
mechanical paddle stirring, a reflux condensor and a thermometer. The reactor was first charged
with 60% of the total weight of water, two third of the emulsifiers and 5% of the D4 monomer
according to the formula given in Table 3. Then, it was heated to 83 ºC using an oil bath while
stirring at 250 rpm under a nitrogen flow. A transparent microemulsion latex was prepared by
adding an initiator solution (5 wt%) into the reactor and continuing the reaction for 30 min.
The pre-emulsion was prepared by adding the remaining D4 monomer, the rest of
emulsifier SDS, co-emulsifier (here AM) and buffer agent to deionized water in the flask with
the stirring speed at 250 rpm. The pre-emulsion was stirred for 15 min and then total amount of
the pre-emulsion was continuously fed into the reactor with the rate of 0.34 mL/h for the next 3
h. Detailed recipes for the preparation of microemulsions and particle sizes are included in Table
3. The reaction conversion was studied by the same process as the one used for the conventional
emulsion polymerization.
Characterizations
Monomer conversion in the time t was calculated using gravimetric method using the equation 1
[5]:
t s 0 sC t = 100 m – m / m – m (1)
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 22
In this equation, mt is the weight of the mass remained, ms is the weight of the DBSA in the
sample, and m0 is the weight of the remained solid in the assumed conversion of 100%.
According to this procedure, monomer concentration in the polymerization time t, ([D4]t) can be
calculated using the C(t) amounts and the equation 2 [5]
:
t 0
D4 = D4 100 – C t / 100 (2)
In this equation, [D4]0 is the initial concentration of D4 in the pre-emulsion of monomer.
Particle size and particle size distributions of the synthesized latexes were measured
using a dynamic light scattering apparatus, DLS, Zetasizer Nano ZS Malvern model. The
samples were diluted with water to 1% solutions and tested at 25 ºC.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 23
REFERENCES
1. Zhuang, Y.Q.; Ke, X.; Zhan, X.L.; Luo, Z.H. Powder. Technol. 2010, 201, 146–152.
2. Gao, X.; Wang, Q.; Sun, H.; Tan, Y.; Zhang, Z.; Xie, Z. Phosphorus, Sulfur Silicon Relat.
Elem., 2014, 189, 1514–1528.
3. Klimisch, H.M. The Analytical Chemistry of Silicones; New York: John Wiley & Sons. USA.
1991; pp. 201-255.
4. Yang, X.; Chen, Z.; Liu, J.; Chen, Q.; Luo, M.; Lai G. Phosphorus, Sulfur Silicon Relat.
Elem., 2016, 191, 117-122.
5. Jiang, S., Qiu, T.; Li, X. Polymer, 2010, 51, 4087-4094.
6. Gunzbourg, D.A.; Favier, J.C.; Hémery, P. Polym. Int. 1994, 35, 179-188.
7. Eaborn, C. and Staynczyk, W.A. J. Chem. Soc. Perkin Trans, 1984, 2, 2099-2103.
8. Suzuki, K.; Andoh, D.; Hyodoh, A.; Satoh, S.; Nomura, M. e-Polymers, 2010, 10, 1, 215-223.
9. Weyenberg, D.R.; Findlay, D.E.; Cekada, J.R.J.; Bey, A.E. J. Polym. Sci.-Polym. Symp. 1969,
27, 27-45.
10. Hyde, J.F.; Wehrly, J.R. US Patent, 1959, 2891920.
11. Gunzbourg, A.D.; Maisonnier, S.; Favier, J.C.; Maitre, C.; Masure, M.; Hémery, P.
Macromol. Symp. 1998, 132, 359-370.
12. Barre`re, M.; Da Silva, S.C.; Balic, R.; Ganachaud, F. Langmuir, 2002, 18, 941-944.
13. Sun, C.N.; Shen, M.M.; Deng, L.L.; Mo, J.Q., Zhou, B.W. Chin. Chem. Lett. 2014, 25, 621–
626.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 24
14. Zhang, D.; Jiang, X.; Yang, C. J. Appl. Polym. Sci. 2003, 89, 3587–3593.
15. Palaprat, G.; Ganachaud, F. C. R. Chimie. 2003, 6, 1385–1392.
16. Halloran, D.J. US. Patent. 2000, 6,071,975.
17. Gee, R.P. US. Patent. 2000, 6,316,541.
18. Onnier, S.M.; Favier, J.C.; Masure, M.; Hémery, P. Polym. Int. 1999, 48, 159-164.
19. Barrère, M.; Maitre, C.; Dourges, M.A.; Hémery, P. Macromolecules, 2001, 34, 7276-7280.
20. Cauvin, S.; Sadoun, A.; Santos, R.D.; Belleney, J.; Ganachaud, F.; Hémery, P.
Macromolecules, 2002, 35, 7919-7927.
21. Cauvin, S.; Ganachaud, F.; Touchard, V.; Hémery, P.; Leising, F. Macromolecules, 2004, 37,
3214-3221.
22. Crespy, D.; Landfester, K. Macromolecules, 2005, 38, 6882-6887.
23. Kostjuk, S.V.; Radchenko, A.V.; Ganachaud, F. Macromolecules, 2007, 40, 482-490.
24. Kumar, A.; Uddin, H.; Kunieda, H.; Furukawa, H.; Harashima, K. J. Dispersion Sci. Tech.
2001, 22, 245–253.
25. Stoffer, J.O.; Bone, T.J. J. Dispersion Sci. Tech. 1980, 1, 37–54.
26. Palaprat, G.; Ganachaud, F. C. R. Chimie. 2003, 6, 1385–1392.
27. Nazir, H.; Lv, P.P.; Wang, L.Y.; Lian, G.P.; Zhu, S.P.; Ma, G.H. J. Coll. Interface Sci.,
2011, 364, 56–64.
28. Lin, M.; Chu, F.; Bourgeat‐Lami, E.; Guyot, A. J. Dispersion Sci. Tech. 2004, 6, 827–835.
29. Garti, N.; Aserin, A.; Wachtel, E.; Gans, O.; Shaul, Y. J. Coll. Interface Sci. 2001, 233, 286–
294.
30. Hill, R.M. Current Opin. Coll. Interface Sci. 2002, 7, 255–261.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 25
31. Zhang, L.; Zhang, C.; Li, G.M. J. Appl. Polym. Sci. 2007, 104, 851–857.
32. Xu, X.J.; Gan, L.M. Current. Opin. Coll. Interface Sci. 2005, 10, 239–244.
33. Ona, I.; Ozaki, M.; Tanaka, O. US. Patent. 1988, 4,784,665.
34. Halloran, D.G. US. Patent. 2000, 6,071,975.
35. Yang, B.; Hui, H.; Riping, C.; Demin, Y. e-Polymers, 2008, 8, 1, 654-661.
36. Leong, Y.S.; Candau, F. J. Phys. Chem. 1982, 86, 22-69.
37. Bleger, F.; Murthy, A.K.; Pla, F.; Kaler, E.W. Macromolecules, 1994, 27, 25-59.
38. Barton, J. Prog. Polym. Sci., 1996, 21, 399-405.
39. Larpent, C.; Tadros, T.F. Coll. Polym. Sci. 1991, 269, 1171-1182.
40. Antonietti, M.; Basten, R.; Lohmann, S. Macromol. Chem. Phys.1995, 196, 466-495.
41. Revis, A. US. Patent. 1996, 5,502,105.
42. Khanjani, J.; Zohuri, G.H.; Gholami, M.; Shojaei, B.; Dalir, R. J. Adhesion, 2014, 90, 174-
194.
43. Eckersley, S.T.; Helmer, B.J. J. Coating Tech., 1997, 69, 864-875.
44. Javaherian Naghash, H.; Karimzadeh, A.; Momeni, A.R.; Massah, A.R.; Alian H. Turk. J.
Chem. 2007, 31, 257-269.
45. Ohtsuka, Y.; Kawaguchi, H.; Sugi, Y. J. Appl. Polym. Sci. 1981, 26, 1637–1647.
46. Chen, S.A.; Lee, S.T. Macromolecules, 1991, 24, 3340–3351.
47. Omidian, H.; Zohuriaan-Mehr, M.J.; Bouhendi, H.; Eur. Polym. J. 2003, 39, 1013-1018.
48. Mather, B.D.; Viswanathan, K.; Miller, K.M.; Long, T.E. Prog. Polym. Sci., 2006, 31: 487–
531.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 26
Table 1. Effects of the main reaction variables on the macroemulsion polymerization of D4 to
achieve the optimized conditions for preparing PDMS latex.
Run
code
Reaction
variable
D4
(g)
DBS
A (g)
Wat
er
(g)
T
(˚C)
Emulsifier Conversio
n (%) &
Rp (mol L-
1s
-1)
Latex
stability Conte
nt (g)
Ratios 3:1
w/w
SL1
DBSA
100.
0
1.63 394 80 4.0 SDS/NP-20 75, 0.050 OLTSa
SL2 100.
0
3.26 393 80 4.0 SDS/NP-20 82, 0.055 Stableb
SL3 100.
0
4.89 391 80 4.0 SDS/NP-20 89, 0.070 Stable
SL4 100.
0
6.52 389 80 4.0 SDS/NP-20 71, 0.064 OLTS
SL5 100.
0
8.15 388 80 4.0 SDS/NP-20 65, 0.065 OLTS
SL6
Emulsifier
s Type
100.
0
4.89 391 80 4.0 DOSS/NP-20 79, 0.073 OLTS
SL7 100.
0
4.89 391 80 4.0 SDBS/NP-20 83, 0.060 Stable
SL8 100.
0
4.89 391 80 4.0 SVS/NP-20 65, 0.033 OLTS
SL9
Emulsifier
Content
100.
0
4.89 391 80 1.0 SDS/NP-20 64, 0.041 OLTS
SL10 100.
0
4.89 391 80 2.0 SDS/NP-20 84, 0.053 Stable
SL11 100.
0
4.89 391 80 3.0 SDS/NP-20 85, 0.057 Stable
SL12 100.
0
4.89 391 80 5.0 SDS/NP-20 88, 0.116 Stable
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 27
(a) Oil layer top seen
(b) Stable: Latex was synthesized with no coagula formed during polymerization nor were lots of
particles (less than 0.2% relative to the total weight of latex) seen after polymerization being
immersed or seen as sediment.
SL13
D4
100.
0
4.89 411 80 4.0 SDS/NP-20 75, 0.048 Stable
SL14 100.
0
4.89 401 80 4.0 SDS/NP-20 79, 0.052 Stable
SL15 100.
0
4.89 381 80 4.0 SDS/NP-20 72, 0.043 OLTS
SL16 100.
0
4.89 371 80 4.0 SDS/NP-20 65, 0.038 OLTS
SL17
Temperatu
re
100.
0
4.89 391 70 2.0 SDS/NP-20 82, 0.058 Stable
SL18 100.
0
4.89 391 75 2.0 SDS/NP-20 84, 0.063 Stable
SL19 100.
0
4.89 391 85 2.0 SDS/NP-20 90, 0.010 Stable
SL20 100.
0
4.89 391 90 2.0 SDS/NP-20 91, 0.126 Stable
SL21c
Agitation
speedd
100.
0
4.89 391 90 2.0 SDS/NP-20 94, 0.056 Stable
SL22 100.
0
4.89 391 90 2.0 SDS/NP-20 93, 0.063 Stable
SL23 100.
0
4.89 391 90 2.0 SDS/NP-20 87, 0.068 Stable
SL24 100.
0
4.89 391 90 2.0 SDS/NP-20 86, 0.065 Stable
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 28
(c) The optimal latex (with the highest stability and maximum conversion) was obtained from
this run in which the average particle diameter was determined to be 88 nm.
(d) Agitation speed for all runs was 150 rpm except for the runs SL21-SL24 for which were 110,
130, 170, and 190 rpm.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 29
Table 2. Effects of the main variables on the microemulsion polymerization reaction of D4 to
achieve the optimized conditions for preparing PDMS latexa.
Run
code
Reaction
variable
D4
(g)
DBSA
(g)
Water
(g)
T
(˚C)
AM
(g)
Feed
rate
(g/h)
Conversi
on (%) &
Rp (mol
L-1
s-1
)
Averag
e
particle
diamet
er (nm)
MSL1
D4
23.0 2.30 203.0 80 0.92 37.28 75, 0.060 59
MSL2 28.7 2.30 197.2 80 0.92 37.28 76, 0.070 55
MSL3 34.5 2.30 191.5 80 0.92 37.28 80, 0.073 52
MSL4 40.2 2.30 185.7 80 0.92 37.28 82, 0.068 57
MSL5 46.0 2.30 179.7 80 0.92 37.28 85, 0.073 54
MSL6
AM
46.0 2.30 180.03 80 0 37.28 68, 0.070 119
MSL7 46.0 2.30 179.8 80 0.23 37.28 85, 0.070 53
MSL8 46.0 2.30 179.5 80 0.46 37.28 86, 0.077 51
MSL9 46.0 2.30 179.3 80 0.69 37.28 87, 0.082 49
MSL1
0
46.0 2.30 178.8 80 1.15 37.28 88, 0.091 40
MSL1
1
DBSA
46.0 3.45 177.7 80 1.15 37.28 87, 0.104 55
MSL1
2
46.0 4.60 176.5 80 1.15 37.28 85, 0.108 56
MSL1
3
46.0 5.75 175.4 80 1.15 37.28 84, 0.050 55
MSL1
4
46.0 6.90 174.2 80 1.15 37.28 83, 0.096 52
MSL1
5 Pre-
emulsified
46.0 4.60 173.1 80 1.15 44.73 82, 0.102 45
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 30
aFor all runs, SDS content and the reaction time was fixed at 1.53 g, and 3h, respectively.
bWhen this reaction was repeated without using AM, conversion, Rp, and average particle
diameter were determined to be 70%, 0.050 mol L-1
s-1
, and 109 nm, respectively. See also the
run MSL6 in which the amount of AM is zero.
MSL1
6
monomer
feeding
rate
46.0 4.60 173.1 80 1.15 55.92 84, 0.102 28
MSL1
7
46.0 4.60 173.1 80 1.15 74.56 86, 0.101 32
MSL1
8
46.0 4.60 173.1 80 1.15 111.84 85, 0.102 37
MSL1
9b
Temperatu
re
46.0 4.60 173.1 70 1.15 55.92 81, 0.085 19
MSL2
0
46.0 4.60 173.1 75 1.15 55.92 82, 0.095 22
MSL2
1
46.0 4.60 173.1 85 1.15 55.92 86, 0.138 48
MSL2
2
46.0 4.60 173.1 90 1.15 55.92 88, 0.145 39
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 31
Table 3. Predetermined recipe of the macroemulsion (conventional emulsion) and
microemulsion polymerization of D4.
Microemulsion Conventional emulsion
Ingredients Feed
(g)
Initial
charge
(g)
Feed
(g)
Initial
charge
(g)
46.0 - 100.0 - D4
0.20 - 0.20 - Sodium
bicarbonate
- 4.6 - 5.0 DBSA
108 72 236 157 Deionized water
0.46 - - - AM
- - 0.5 - Iconol NP-20
1.5 - 1.5 - SDS
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 32
Figure 1. Effect of DBSA concentration on macroemulsion polymerization conversion of D4
while 2 wt% of SDS/NP-20 (3:1 w/w) hybrid emulsifier has been used (See Table 2, Runs SL1-
SL5) (graphs a and b). Conversion versus polymerization time in lieu of different hybrid
emulsifiers (c) and content of the emulsifier mixture of SDS and NP-20 (d) while a fixed DBSA
0.03 mol/L has been employed.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 33
Figure 2. Effect of (a) AM concentration, (b) DBSA concentration, (c) pre-emulsified monomer
feeding rate and (d) temperature on conversion of the microemulsion polymerization of D4.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 34
Figure 3. Arrhenius plot of lnRp versus 1/T the polymerization of D4 in (a) conventional
system, and (b) microemulsion system.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 35
Figure 4. The particle size distribution and appearance for typical samples prepared from (a)
macroemulsion (run SL21) and (b) microemulsion (run MSL22) system.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 36
Figure 5. Microemulsion polymerization of D4 according to the run MSL12 given in Table 3.
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 37
Figure 6. Macroemulsion polymerization of D4 according to the recipe of the sample SL10 given
in Table 2.
