Photodegradative surfactants: p-dodecylbenzyltrimethylammonium bromide as a photodegradative emulsifier for microemulsion polymerization

Article abstract of DOI:10.1246/cl.2005.814

A photodegradative surfactant, p-dodecylbenzyltrimethylammonium bromide, was used as an emulsifier for micro-emulsion polymerization of methyl methacrylate in water. The resulting polymer latex was coagulated during UV irradiation. The analysis of the centrifuged solid after irradiation indicated almost perfection of both recovery of the polymer and removal of surface-active species from it. Copyright

Full text of DOI:10.1246/cl.2005.814

814
Chemistry Letters Vol.34, No.6 (2005)
Photodegradative Surfactants: p-Dodecylbenzyltrimethylammonium Bromide
as a Photodegradative Emulsifier for Microemulsion Polymerization
Yoshihiro Itoh,ꢀ Satoshi Horiuchi, and Kenji Yamamoto
Department of Functional Polymer Science, Faculty of Textile Science and Technology,
Shinshu University, 3-15-1 Tokida, Ueda 386-8567
(Received March 29, 2005; CL-050419)
A photodegradative surfactant, p-dodecylbenzyltrimethyl-
ammonium bromide, was used as an emulsifier for micro-emul-
sion polymerization of methyl methacrylate in water. The result-
ing polymer latex was coagulated during UV irradiation. The
analysis of the centrifuged solid after irradiation indicated al-
most perfection of both recovery of the polymer and removal
of surface-active species from it.
Irrad.
(a) before
(b) after
In emulsion polymerization, surfactants are essential for
emulsification of monomer droplets and stabilization of latex
particles, but they have drawbacks in latex applications such
as reduced water-resistance and electrical insulation of coatings.
A simple way to overcome these problems is emulsifier-free
polymerization. In most cases, however, small or moderate
amounts of additives (e.g., polymerizable emulsifiers) have been
added,1 and then ‘‘truly’’ surfactant-free polymers have been
scarcely obtained. An alternative and promising approach
involves the use of cleavable surfactants.2 Yamamura et al.3
demonstrated that acid-hydrolyzable surfactants containing ketal
and sulfonate groups lower the content of ionic species in the
resulting polymer. Nuyken et al.4 reported that p-dodecylphenyl-
diazosulfonate can control the latex coagulation process simply
by exposing the dispersion to UV irradiation.5
Figure 1. Photographs of PMMA/C12BA latex solution (a)
before and (b) after UV irradiation for 90 min.
COOCH3
(a) Before irradiation
terephthalonitrile
TMS
+
N(CH3)3
CDCl3
Phenyl
CH2
N
In this paper, we report that a photodegradative surfac-
tant, p-dodecylbenzyltrimethylammonium bromide (C12BA)
(Scheme 1),6 can be used not only as an emulsifier for micro-
emulsion polymerization of methyl methacrylate (MMA) but
also as a useful ‘‘flocculant’’ of latices that gives surfactant-free
polymers.
(b) After irradiation
(precipitate)
Phenyl
C12H25
CH2 N(CH3)3 Br
C12BA
(c) After irradiation
(supernatant)
+
NH(CH3)3
Scheme 1.
Poly(MMA) (PMMA) latices were prepared according to
the method of Ming et al.7 with some modification.8 The poly-
merization proceeded smoothly and the conversion went up to
over 95%. The resulting transparent latex solution was stable
over several weeks.
+
NH2(CH3)2
The latex solution became turbid after UV irradiation for
20 min, its turbidity reached to the maximum after 45 min, and
then the polymer was partially precipitated (Figure 1).9 This
clearly indicates that in the time range the conversion of C12BA
to a non-surfactant labilizes the latices, promoting their coagula-
tion. By contrast, no apparent change was observed for the lati-
ces prepared with a non-degradative surfactant, hexadecyltri-
methylammonium chloride, or a photodegradative one, hexade-
8
7
6
5
4
3
2
1
0
ppm
Figure 2. 1H NMR spectra of PMMA/C12BA lattices dissolved
in CDCl3 (a) before irradiation, (b) precipitate after irradiation,
and (c) supernatant after irradiation: terephthalonitrile (ꢀ 7.80
ppm) and tetramethylsilane (TMS: ꢀ 0.00 ppm) were added as
internal standards.
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.6 (2005)
815
Table 1. Yields (%) of species in irradiated C12BA/PMMA
latex solution
Table 2. Product yields (%) for photolysis of C12BA in PMMA
latex and H2Oa
Irrad.a
Fraction
PMMAb C12BAc Hydrophobed Ione
Sample Conversionb Alcohol Alkyl sec-A tert-A
Before Total
After Total
100
100
96
100
4
3
—
86
79
0
—
93
3
latex
C12BA
85
95
7
9
26
23
32
37c
4
57c
Precipitate
Supernatant
a[C12BA] ¼ 10 mM; [PMMA] ¼ 26 mM; irradiation time,
60 min; products yields are based on the initial C12BA concen-
tration; Alcohol, p-dodecylbenzyl alcohol; Alkyl, p-dodecyl-
toluene; sec-A, dimethylammonium bromide; tert-A, trimethyl-
ammonium bromide. bConversion yield of C12BA in %.
cIrradiation time, 90 min.
4
0
68f
a[C12BA] ¼ 3 mM; [PMMA] ¼ 29 mM; irradiation time, 90
min; products yields are based on the initial C12BA concentra-
b
c
tion. Determined by peak area at 3.60 ppm. Determined by
peak area at 3.42 ppm. dTotal yield of p-dodecylbenzyl alcohol,
p-dodecyltoluene, and other minor products determined by
peak area at 2.55 ppm. eTotal yield of dimethyl- and trimethyl-
ammonium bromides, determined by peak areas at 2.73 and
polymer industry. For improvement of the reactivity and the
sensitivity to a longer-wavelength light (>300 nm), the synthesis
of different surfactants is in progress.
f
2.89 ppm, respectively. Partially insoluble in CDCl3.
cylbenzyldimethylammonium chloride.6 This is because the lati-
ces still hold a surface-activity after irradiation.
This work was supported by a Grant-in-Aid for 21st Century
COE Program from the Ministry of Education, Science, Sports,
and Culture of Japan.
After irradiation for 90 min (almost 100% conversion), the
suspended PMMA/C12BA solutions were centrifuged and the
precipitate and supernatant were analyzed by 1H NMR spectros-
copy.10 Figure 2 shows the spectra where some of assigned struc-
tures are indicated. Table 1 summarizes the quantitative data. As
described below, the photoproducts of C12BA obtained in the
latex were the same as those in water. The signals of PMMA
(ꢀ 0.8–2.1 ppm and 3.60 ppm) were observed in the precipitate
(Figure 2b), whereas those in the supernatant were little
(Figure 2c). In fact, the recovery of the polymer, calculated from
the area for the methyl proton at 3.60 ppm, was 96% of the total.
Most of the signal of the N-methyl proton in C12BA at 3.42 ppm
disappeared both in the precipitate and supernatant, and those of
the corresponding water-soluble products, dimethyl- and tri-
methylammonium bromides (2.73 ppm and 2.89 ppm, respec-
tively) in the supernatant. In the same manner, the benzene pro-
tons in C12BA (7.2–7.6 ppm) disappeared, and those of the cor-
responding hydrophobic products, p-dodecylbenzyl alcohol, p-
dodecyltoluene, and others (7.0–7.2 ppm), appeared in the pre-
cipitate. From those data, the conversion of C12BA was deter-
mined to be 96% and the removal of ionic species from the pre-
cipitate to be at least 94% (Table 1). Therefore, the photolysis of
C12BA not only can recover the polymer but also can remove
ionic species from it almost perfectly. It should be noted that
salting-out of the unirradiated PMMA/C12BA latex with aque-
ous saturated NaCl solution recovered 87% of the total polymer
and removed only 15% of C12BA from it. Such a large difference
in ionic content would affect the performances of the resulting
polymers. Preliminary experiments showed that ionic dyes were
little adsorbed on the film and solid of the ‘‘photo’’-precipitated
polymer, though, containing some photo-products. This might
be indicative of improved water-resistance or electrical insula-
tion of the polymer coating.11
References and Notes
1
2
3
4
5
6
7
8
X. J. Xu, H. L. Goh, K. S. Siow, and L. M. Gan, Langmuir,
17, 6077 (2001).
M. Stjerndahl, D. Lundberg, and K. Holmberg, Surf. Sci.
Ser., 114, 317 (2003).
S. Yamamura, M. Nakamura, K. Kasai, H. Satoh, and
T. Takeda, Yukagaku, 40, 1002 (1991).
O. Nuyken, K. Meindl, A. Wokaun, and T. Mezger, Macro-
mol. Rep., A32, 447 (1995).
Characterization of precipitates (polymers) such as surfac-
tant content has not been reported.
Y. Itoh, K. Yamamoto, and H. Shirai, Chem. Lett., 32, 8
(2003).
W. Ming, F. N. Jones, and S. Fu, Polym. Bull., 40, 749
(1998).
A typical polymerization procedure was as follows: To a
mixture of 0.5 g of MMA, 0.6 g of C12BA, and 45 g of water
a 0.04 g of 2,20-azobis(2-isobutylamidine) dihydrochloride
in 5 g of water was added and heated to 60 ꢁC under nitrogen
atmosphere. Then 1 g of MMA was slowly added into the
solution, which was kept at 60 ꢁC for another 3.5 h. A portion
of the resulting latex solution was lyophilized and weighed.
The polymerization yield was 97%. The weight-average
molecular weight of the obtained polymer was determined
to be 80,000 by GPC.
9
The diluted polymer latex solution ([C12BA] ¼ 3 mM) in a
quartz tube (13 mmꢁ) was irradiated without deaeration at
25 ꢁC with all light emitted from a 500-W high-pressure
mercury lamp in a merry-go-round apparatus.
10 Irradiated samples were prepared as follows: the suspended
solutions were centrifuged and the precipitate was dissolved
in CDCl3 containing a known amount of terephthalonitrile as
an internal standard (ꢀ 7.80 ppm). The supernatant solution
was lyophilized and then re-dissolved in the above CDCl3
solution. Non-irradiated samples were obtained by direct
lyophilization or salting-out with NaCl followed by dissolu-
tion in CDCl3.
The photoreactivities of C12BA in the latex and H2O are
compared in Table 2.12 Although the conversion of C12BA
slightly decreased in the latex, the same products were obtained
and their yields were not much different. It is thus concluded that
C12BA in the polymer latex is photodegradated similarly to that
in water (quantum yield = 0.45).6
In conclusion, the irradiation of the PMMA/C12BA latex
can precipitate the polymer and can remove ionic species from
it almost quantitatively, which may find various applications in
11 Detailed characterization of the polymers is in progress.
12 The latex composition was slightly different from the above
case.
Published on the web (Advance View) May 14, 2005; DOI 10.1246/cl.2005.814